Annotated Bibliography for Parasitic Birds of Genus Molothrus

Ahlers, D. and R. Tisdale. In preparation. Cowbird control program, Middle Rio Grande, New Mexico, 1998. U.S. Bureau of Reclamation, Albuquerque Area Office, New Mexico, and Technical Service Center, Denver, Colorado.

Results from a third year of an intensive cowbird trapping program are presented. A nest monitoring study of potential host species was also initiated. Preliminary data compare parasitism rates between the trapping area, adjacent Bosque Del Apache National Wildlife Refuge lands, and on adjacent lands subject to annual grazing by livestock. Point count data results from these three areas showing relative distribution and abundance are also discussed.

Keywords: brood parasitism, distribution, host species, population control, trapping, abundance

Ahlers, D. and R. Tisdale. In preparation. Brown-headed cowbird movements and distribution within the Middle Rio Grande Basin, New Mexico, 1998. U.S. Bureau of Reclamation, Albuquerque Area Office, New Mexico and Technical Service Center, Denver, Colorado.

Radiotelemetry was used to track daily and seasonal movements of brown-headed cowbirds within the Middle Rio Grande Basin of central New Mexico. Preliminary data suggest riparian habitat of the Middle Rio Grande provided all the daily feeding and breeding requirements for brown-headed cowbirds; cowbirds rarely ventured far from the host-rich riparian areas. Point count data collected from adjacent riparian areas on the Bosque Del Apache National Wildlife Refuge, areas with annual grazing by livestock, and areas within the trapping area are also discussed.

Keywords: radio telemetry, distribution, movements

Airola, D. A. 1986. Brown-headed cowbird parasitism and habitat disturbance in the Sierra Nevada. J. Wildl. Manage. 50:571-575.

Brood parasitism by the brown-headed cowbird based on available human- and livestock-based food sources, was assessed in the northern Sierra Nevada. Parasitism was strongly associated with habitat disturbance; 27.1% of groups of susceptible host species in highly

disturbed areas contained cowbird chicks vs. 8.7% in less disturbed areas. Parasitized nests

contained 76% fewer host chicks than unparasitized nests. Riparian obligate host species are more susceptible to population declines as a result of brood parasitism.

Keywords: brood parasitism, host species, California

Alberger, A. H. 1890. The cowbird. Ornithol. and Oologist 15:46.

A first-person account adds the purple finch to the list of potential cowbird hosts.

Keywords: host species

Allan, S. E. and R. A. Suthers. 1994. Lateralization and motor stereotypy of song production in the brown-headed cowbird. J. Neurobiol. 25:1154-1166.

Cross-correlation analyses reveal that individual cowbirds produce each of their four to seven song types with a distinct stereotyped motor pattern. The acoustic variations between song types are reflected in the differences in the bronchial airflow and air sac pressure patterns associated with song production. These motor skills may be especially important in producing behaviorally effective song.

Keywords: vocalization, Indiana

Amadon, D. 1940. Hosts of the cowbird. Auk 57:257.

The author summarizes three additions of shiny and bronzed cowbird host species to previously published lists.

Keywords: bronzed cowbird, shiny cowbird, host species

Anderson, J. F. and W. Glowa. 1985. Diazinon poisoning of brown-headed cowbirds. J. Field Ornithol. 56:407-408.

Two separate cases of diazinon poisonings of brown-headed cowbirds in Connecticut were reported in 1983 and 1984, possibly as a result of diazinon application to lawns. Diazinon, a broad spectrum insecticide, is highly toxic to insects and birds. Although field poisonings of ducks and geese have been reported, the authors are unaware of documented accidental poisonings of passerine birds.

Keywords: mortality, Connecticut

Ankney, C. D. and D. M. Scott. 1980. Changes in nutrient reserves and diet of breeding brown-headed cowbirds. Auk 97:684-696.

Female brown-headed cowbirds in southwestern Ontario were collected in 1976 to determine the relative importance of nutrient reserves and dietary nutrients to egg laying. Males were also collected and used as controls. Results showed that females stored neither fat nor protein before they began egg laying, nor utilized fat or protein reserves for egg production. However, calcium reserves of females did increase prior to egg laying. During the breeding season, females shifted their diet to include a higher percentage of insects than the males did. The study concludes that female cowbirds obtain the nutrients necessary for egg production directly from their diet. The importance of this study to the egg-laying pattern of female cowbirds is discussed.

Keywords: diet, Ontario, Canada

Ankney, C. D. and D. M. Scott. 1982. On the mating system of brown-headed cowbirds. Wilson Bull. 94:260-268.

A hypothesis that the mating pattern of brown-headed cowbirds includes both monogamy and promiscuity is discussed. The study results are based on observations of social groupings and weights of adult and yearling males, and on published observations of social behavior of cowbirds. It is believed that males use two tactics to obtain copulations. The first is to guard a female from other males and monopolize her copulations. The second is to be a sneaky male and steal copulations from paired males. This hypothesis is supported because: (1) the sex ratio of 1.5 males to 1 female excludes many males from being paired; (2) females have no apparent reason to be faithful to the paired male and may increase their fitness by copulating with sneaky males; and (3) females are continuously fertile for 8 weeks, thus sneaky males have many opportunities to steal copulations.

Keywords: mating system, social organization, Ontario, Canada

Ankney, C. D. and S. L. Johnson. 1985. Variation in weight and composition of brown-headed cowbird eggs. Condor 87:296-299.

Study determined the variation in weight and composition of brown-headed cowbird eggs; compared this variation with data from other altricial birds; and determined seasonal patterns in egg weight. Sixteen eggs from a single female were collected and the variation in egg weight and composition within and among females is also discussed. Data indicate the composition of cowbird eggs is typical of that of eggs of other altricial species.

Keywords: fecundity, eggs, Ontario, Canada

Ankney, C. D. and D. M. Scott. 1988. Size of digestive organs in breeding brown-headed cowbirds, Molothrus ater, relative to diet. Can. J. Zool. 66:1254-1257.

In 1976, male and female brown-headed cowbirds were collected before, during, and after the egg-laying season in southwestern Ontario. The gizzards, livers, and small intestines were measured and compared. Results indicate gizzard weights decreased when the birds fed primarily on arthropods and increased when they fed primarily on seeds. The length of the intestines, particularly of females, was highest when the diet included the least amount of plant material. Only subtle changes in liver weight were found. The authors conclude that attempts to assess changes in diet quality of wild passerines by looking at changes of the size of digestive organs should be done cautiously, particularly if baseline data are from captive birds.

Keywords: diet, Ontario, Canada

Arcese, P., J.N.M. Smith, and M. I. Hatch. 1996. Nest predation by cowbirds and its consequences for passerine demography. Proc. Natl. Acad. Sci. USA. 93:4608-4611.

The study tested the hypothesis that parasitism and predation are often linked since brown-headed cowbirds depredate nests discovered late in the host's nesting cycle possibly to enhance future opportunities for parasitism. An experiment mimicking egg ejection by brown-headed cowbirds did not affect nest failure. Results were contrary to the prediction that predation facilitates future parasitism. Naturally parasitized nests failed less often than unparasitized nests. Higher survival of parasitized nests is expected under the cowbird predation hypothesis when female cowbirds defend nonfeeding areas. Cowbirds often depredate unparasitized nests but do not depredate nests they have laid in.

Keywords: brood parasitism, predation, egg manipulation, British Columbia, Canada

Arnold, K. A. and D. M. Johnson. 1983. Annual adult survival rates for brown-headed cowbirds wintering in southeast Texas. Wilson Bull. 95:150-153.

This study was conducted to determine if brown-headed cowbird winter mortality rates differed between southeast Texas and the population as a whole. The roosts studied from 1969 to 1981 are near the southern limit of the winter range of Molothrus ater. The authors conclude that migrating farther south offers some survival advantage, especially for females; they appear to experience considerably better survivorship during the winter than did the males with whom they communally roost (63% vs. 53%).

Keywords: mortality, migration, Texas

Austin, O. L. 1932. A cowbird attempts to parasitize barn swallows. Bird-Banding 3:178-179.

This is a first-person account of barn swallows aggressively driving a brown-headed cowbird away from their nest in Massachusetts in 1932. The swallows comparative immunity of being a host may be due to their habit of attending their nests closely.

Keywords: host defense, host species

Averill, A. 1996. Brown-headed cowbird parasitism of neotropical migratory songbirds in riparian areas along the Lower Colorado River. M.S. thesis. School of Renewable Natural Resources, University of Arizona, Tucson.

The author evaluated the parasitism rates of four riparian obligate species along the Lower Colorado River and compared these rates to the surrounding vegetation. Parasitism rates ranged from 40 to 90% for the four species. The author believes the density of vegetation surrounding the nest site may be related to the cowbirds ability to locate nests and host selection.

Keywords: brood parasitism, host species, Arizona, California

Bailey, B. 1914. Cowbirds eggs. Oologist 31:143.

This is a first-person account of finding cowbird eggs in the nests of 11 species in Minnesota and Montana in 1913.

Keywords: brood parasitism, host species

Baird, J. 1958. The postjuvenal molt of the male brown-headed cowbird (Molothrus ater). Bird-Banding 29:224-228.

Evidence is presented that the postjuvenal molt of the male brown-headed cowbird is not complete. The author gives an order of the molted feather tracts.

Keywords: morphology, Rhode Island

Baltz, M. E. and D. E. Burhans. 1998. Rejection of artificial parasite eggs by gray kingbirds in the Bahamas. Condor 100:566-568.

The authors added artificial shiny cowbird eggs to gray kingbird nests in the Bahamas, where shiny cowbirds were first recorded in 1993. Gray kingbirds ejected 85% of artificial eggs within 48 hours of addition. Based upon the short time of contact between the two species, the authors suggest that egg ejection behavior by gray kingbirds in the Bahamas has been retained from ancestral populations.

Keywords: shiny cowbird, Bahamas, host defense

Baptista, L. F. 1972. Cowbird parasitism on the white-crowned sparrow and wren-tit in the San Francisco Bay area. Auk 89:879-882.

A first-person account of the first recorded parasitism of the race nuttalli by the brown-headed cowbird in 1969 that documents 10 parasitized broods totaling 14 juvenile cowbirds and 1 cowbird egg in sparrow nests.

Keywords: host species, California

Baker, M. D. and M. J. Lacki. 1997. Short-term changes in bird communities in response to silvicultural prescriptions. Forest Ecology and Management 96:27-36.

Bird communities were surveyed on the Daniel Boone National Forest, Kentucky, using standardized point counts in May and June of 1993, 1994, and 1995. Pre-harvest surveys revealed no differences in abundance, richness, or diversity of bird communities among stands. After harvest, all indices were higher for bird communities in harvested stands than in no-harvest stands, with no difference among clear-cut or two-age stands. The brown-headed cowbird was the most commonly detected species following harvest.

Keywords: habitat, abundance, Kentucky

Barber, D. R. and T. E. Martin. 1997. Influence of alternate host densities on brown-headed cowbird parasitism rates in black-capped vireos. Condor 99:595-604.

Parasitism rates relative to the density of individual host species and densities of coexisting host species are discussed. The authors monitored 392 nests among coexisting host species and measured their densities among six habitats on Fort Hood Military Reservation, Texas, from 1991-1992 to test the hypothesis that coexisting species affect parasitism rates of the endangered black-capped vireo. Parasitism rates in the vireo were positively correlated with cumulative host density in general, and with northern cardinal densities in particular. Cowbirds may be attracted to conspicuous species, such as cardinals, and high densities of such species may negatively affect coexisting species by increasing the potential for parasitism.

Keywords: brood parasitism, host species, Texas

Bazin, R. C. and S. G. Sealy. 1993. Experiments on the responses of a rejector species to threats of predation and cowbird parasitism. Ethology 94:326-338.

In 1989 and 1990, the authors presented freeze-dried models of a nondescript sparrow (control), a female brown-headed cowbird, and an avian nest predator to nesting eastern kingbirds at Delta Marsh, Manitoba, during the egg-laying and nestling stages to evaluate nest defense as a mechanism to reduce the potential of parasitism by the brown-headed cowbird. Kingbirds responded aggressively toward the cowbird model, less to the control, and least to the predator model. Results suggest that kingbirds in this area did not recognize the cowbird as a significant threat due to the relatively low potential of the kingbird to serve as a host.

Keywords: host defense, host species, Manitoba

Beane, J. C. and S. L. Alford. 1990. Destruction of a pine warbler brood by an adult cowbird. Chat 54:85-87.

This is a first-person account of an adult cowbird deliberately ejecting a brood of pine warblers from a nest that did not contain a cowbird chick on April 29, 1990, in Brunswick County, North Carolina.

Keywords: behavior, North Carolina

Beezley, J. A. and J. P. Rieger. 1987. Least Bell's vireo management by cowbird trapping. Western Birds 18:55-61.

To promote the survival of the least Bells vireo, the California Department of Transportation began a trapping program for brown-headed cowbirds along the Sweetwater River of San Diego County in 1986. This article addresses the present U.S. Fish and Wildlife Service management method for reducing brood parasitism of vireos through the trapping and removal of cowbirds. The authors contend that the present management program does not fully consider the behavior or ecology of the cowbird.

Keywords: population control, trapping, California

Behrendt, I. 1960. Note on cowbird behavior. Bull. Scarsdale Audubon Soc. 14:6.

Keywords: behavior

Bell, R. K. 1992. The cowbird dilemma. Redstart 59:54-60.

The author gives a summary of the natural history of the cowbird and how individuals can help promote Amore desirable@ avian species.

Keywords: brood parasitism, population control

Bell, R. 1993. The cowbird dilemma. Pennsylvania Birds 6:147.

This report is a first-person observation of the decline of many songbirds and the increase in brown-headed cowbirds.

Keywords: brood parasitism

Bendire, C. E. 1893. The cowbirds. Report U.S. Natl. Mus. for year ending June 30, 1893:589-624.

This report includes the authors articles written for Life Histories of North American Birds, Part II, and an addition of a concise description of each species, taken from R. Ridgeways Manual of North American Birds. The articles on the cowbirds found in the Argentine Republic are copied from Messrs. P. L. Sclater and W. H. Hudsons work on Argentine ornithology. The notes on their habits are based on observations made by W. H. Hudson.

Keywords: morphology, life history

Benson, S. B. and W. C. Russell. 1934. The cowbird breeds in Berkeley. Condor 36:219.

The authors describe the observation and collection of the first recorded cowbird in Berkeley, California, and the first record of the western flycatcher as a host for this species in 1934. The cowbird chick, soliciting feedings by birds of several other species, was also observed.

Keywords: host species, range expansion, California

Bent, A. C. 1958. Life histories of North American blackbirds, orioles, tanagers, and allies. U.S. Natl. Mus. Bull. 211.

Keywords: life history

Berger, A. J. 1948. Early nesting and cowbird parasitism of the goldfinch in Michigan. Wilson Bull. 60:52-53.

A first-person discovery in 1947 of two goldfinch nests in which the host had buried brown-headed cowbird eggs.

Keywords: host defense, host species, Michigan

Berger, A. J. 1951. The cowbird and certain host species in Michigan. Wilson Bull. 63:26-34.

From April 1, 1946, through September 30, 1949, the author studied the cowbird in Washtenaw County, Michigan. During 4 breeding seasons, nests of 72 various bird species were observed. Twenty of these species were parasitized by brown-headed cowbirds. Two other species were also likely parasitized. Pertinent data concerning the breeding season of certain host species and the relative success of parasitized and nonparasitized nests are presented.

Keywords: host species, Michigan

Berger, A. J. and D. F. Parmelee. 1952. The alder flycatcher in Washtenaw County, Michigan: breeding distribution and cowbird parasitism. Wilson Bull. 64:33-38.

In 1951, the authors conducted a survey of the alder flycatcher. They found the incidence of cowbird parasitism (20.8% of 48 nests) considerably higher than in recent southern Michigan observations.

Keywords: host species, Michigan

Berger, A. J. 1955. Six-storied yellow warbler nest with eleven cowbird eggs. Jack-Pine Warbler 33:84.

On June 11, 1955, near Remus, Michigan, the author found a deserted yellow warbler nest with 11 buried cowbird eggs.

Keywords: host species, Michigan

Berger, A. J. 1960. Some uncommon cowbird hosts. Jack-Pine Warbler 38:118.

This report describes the first-person observations of six infrequent hosts (mourning dove, eastern kingbird, great crested flycatcher, Acadian flycatcher, Traills flycatcher, and American goldfinch) near Ann Arbor, Michigan, from 1950 to 1959.

Keywords: host species, Michigan

Bielefeldt, J. and R. N. Rosenfield. 1997. Reexamination of cowbird parasitism and edge effects in Wisconsin forests. J. Wildl. Manage. 61:1222-1226.

The authors evaluated parasitism rates by brown-headed cowbirds on the nests of Acadian flycatchers in relation to distance of hosts nests to nonforest openings in the Kettle Moraine State Forest of southeastern Wisconsin from 1991-1994. They also reexamined and compared the results of this study to these (and other) species of songbirds in an oft-cited paper by Brittingham and Temple (1983). They reported a significant increase of parasitism with the proximity of host nests to nonforest openings on another southern Wisconsin study area. The Wisconsin data reported and reexamined here do not support the proposition that parasitism rates on forest-interior birds decrease with an increasing distance from forest edges and openings over distances of 300 m for openings 0.2 ha in size.

Keywords: brood parasitism, habitat, Wisconsin

Blankespoor, G. W., J. Oolman, and C. Uthe. 1982. Eggshell strength and cowbird parasitism of red-winged blackbirds. Auk 99:363-365.

In 1975 and 1976, the authors monitored brown-headed cowbird parasitism in populations of an acceptor species, the red-winged blackbird, in Lincoln County, South Dakota. They compared the shell strength of cowbird eggs and blackbird eggs as an adaptation for brood parasitism.

Keywords: brood parasitism, eggs, host species, South Dakota

Bleitz, D. 1956. Heavy parasitism of blue grosbeaks by cowbirds in California. Condor 58:236-238.

In four separate seasons, from 1948 to 1951, the author observed and kept notes on a small group of blue grosbeaks nesting along the edges of a small tidal bay near Balboa, Orange County, California. In 1949, seven nesting attempts produced only two young grosbeaks. Cowbird parasitism rates appeared to be consistent throughout the length of the study, however since fewer site visits were conducted in subsequent seasons, field notes were too incomplete to afford an estimate of nesting success.

Keywords: brood parasitism, host species, California

Blincoe, B. J. 1935. A cowbird removes a robins egg. Wilson Bull. 47:158.

A first-person observation in Ohio of a brown-headed cowbird removing an egg from an American robins nest in 1934.

Keywords: host species, Ohio

Blocher, A. 1924. Song-sparrow-cowbird. Oologist 41:9-10.

A first-person account of a song sparrow nest with two host eggs and seven cowbird eggs in Illinois.

Keywords: host species, Illinois

Blocher, A. 1936. Cowbirds. Oologist 53:131-133.

Keywords: life history, host species

Bonwell, J. R. 1895. A strange freak of the cowbird. Nidiologist 2:153.

A first-person account of a female brown-headed cowbird feeding only its young in the nest of a host species while host young were present.

Keywords: behavior

Bowers, R. K. Jr. and J. B. Dunning, Jr. 1984. Nest parasitism by cowbirds on buff-breasted flycatchers, with comments on nest-site selection. Wilson Bull. 96:718-719.

This report discusses previously unrecorded cowbird parasitism on buff-breasted flycatchers in 1982, and suggests the flycatcher's only defense is nest-site selection.

Keywords: brood parasitism, host species, nest-site selection

Boxall, P. C. 1981. Ruby-crowned kinglets (Regulus calendula) feeding a brown-headed cowbird (Molothrus ater). Can. Field-Nat. 95:99-100.

A first-person account of a cowbird chick being fed by a pair of ruby-crowned kinglets in British Columbia in 1979. The kinglet was previously thought to be a rare host, but may be more common than expected.

Keywords: host species, British Columbia, Canada

Brackbill, H. 1976. A brown-headed cowbird in postjuvenal molt at age of about 38 days. Bird-Banding 47:275-276.

A first-person observation of a molting brown-headed cowbird that was approximately 38 days old.

Keywords: morphology

Braden, G. T. and R. L. McKernan. 1997. Effects of nest parasitism by the brown-headed cowbird on nesting success of the California gnatcatcher. Condor 99:858-865.

California gnatcatcher nests were examined to determine the effects of brown-headed cowbird trapping on nest parasitism and nest success. The study was conducted from 1992 to 1995 at five sites in western Riverside County, California. Prior to cowbird trapping, nest parasitism was 31.5% over the entire breeding season and 45.7% during the period when cowbirds were active. Considering nest fates regardless of initiation date, there were no significant differences between the trapping and nontrapping periods. The increase in nest success from decreased nest parasitism was negated by an increase in nest abandonment before cowbirds were active.

Keywords: brood parasitism, trapping, population control, California

Brandt, A. E. 1947. The rearing of a cowbird by Acadian flycatchers. Wilson Bull. 59:79-82.

This account documents the rearing of a single cowbird chick from the nest of an Acadian flycatcher on the Edwin S. George Reserve, near Pinckney, Livingston County, in southeastern Michigan during the summer of 1946.

Keywords: brood parasitism, host species, Michigan

Briskie, J. V. and S. G. Sealy. 1987. Responses of least flycatchers to experimental inter- and intraspecific brood parasitism. Condor 89:899-901.

The authors documented the behavioral responses of least flycatchers at Delta Marsh, Manitoba, to artificial eggs placed in their nests. Nests were artificially parasitized from the period of nest construction through the nestling stages from 1984 to 1986.

Keywords: brood parasitism, host species, egg manipulation, Manitoba, Canada

Briskie, J. V. and S. G. Sealy. 1989. Changes in nest defense against a brood parasite over the breeding cycle. Ethology 82:61-67.

The behavior of nesting least flycatchers to a model of the brown-headed cowbird at Delta Marsh, Manitoba, Canada, in 1986, was observed and documented. Flycatchers were more likely to give threat displays during laying when the consequences of brood parasitism were greatest; however, the intensity of all other defensive behavior did not significantly change throughout the nesting cycle. Least flycatchers were aggressive toward cowbirds throughout the nesting cycle because cowbirds prey on both eggs and nestlings.

Keywords: host defense, Manitoba, Canada

Briskie, J. V. and S. G. Sealy. 1990. Evolution of short incubation period in the parasitic cowbirds, Molothrus spp. Auk 107:789-794.

An evaluation of mean cowbird incubation periods reveals that a 10-day incubation period may represent the absolute minimum for this species.

Keywords: eggs, incubation

Briskie, J. V., S. G. Sealy, and K. A. Hobson. 1990. Differential parasitism of least flycatchers and yellow warblers by the brown-headed cowbird. Behav. Ecol. Sociobiol. 27:403-410.

The authors documented that least flycatchers responded more aggressively than yellow warblers to a model female cowbird at the nest and concluded that greater nest defense by flycatchers may reduce the rate of brood parasitism. The results suggest the large difference in parasitism rates between these two hosts was primarily a product of nest location, however differences in host nest-defense and breeding asynchrony may have contributed to preferential host selection.

Keywords: brood parasitism, host species, host defense

Briskie, J. V., S. G. Sealy, and K. A. Hobson. 1992. Behavioral defenses against avian brood parasitism in sympatric and allopatric host populations. Evolution 46:334-340.

The authors conducted an experimental parasitism study that supports the hypothesis that recognition of cowbirds and their eggs evolved as adaptations to counter cowbird parasitism and not some other selection pressure. The results suggest that an expression of anti-parasite defenses by allopatric individuals may be genetic.

Keywords: brood parasitism, host defense

Brittingham, M. C. and S. A. Temple. 1983. Have cowbirds caused forest songbirds to decline? BioScience 33:31-35.

A review of existing information on brown-headed cowbirds within the eastern deciduous forest suggests that ecological factors may determine the rate of parasitism on forest songbirds. Temporal, spatial, and biogeographic correlations may increase the potential for brood parasitism in declining forest songbird populations.

Keywords: brood parasitism, nest-site selection, Wisconsin

Brittingham, M. C. and S. A. Temple. 1996. Vegetation around parasitized and non-parasitized nests within deciduous forest. J. Field Ornithol. 67:406-413.

Vegetation in 0.04-ha circles around 93 nests from 12 forest-dwelling neotropical migrants was quantified to determine whether the structure of the vegetation influenced the potential for parasitism from brown-headed cowbirds. The results suggest that species nesting within small forest openings may be particularly vulnerable to cowbird parasitism.

Keywords: brood parasitism, host species, host defense

Brooker, M. G. and L. C. Brooker. 1991. Eggshell strength in cuckoos and cowbirds. Ibis 133:406-413.

The authors suggest that the advantage of a strong eggshell in the cuckoo and cowbird species is to protect the parasites egg from damage if the nest is parasitized on multiple occasions. This suggestion relies on the observation that cuckoo and cowbird species may commonly lay more than one egg per nest and often remove or can damage their own eggs in the process.

Keywords: eggs

Broughton, K. E., A.L.A. Middleton, and E. D. Bailey. 1987. Early vocalizations of the brown-headed cowbird and three host species. Bird Behaviour 7:27-30.

The vocalizations of nestling and newly fledged brown-headed cowbirds from eight nests were recorded, analyzed, and compared to those of the host's young to determine if cowbirds mimic their nest mates. Sonagrams showed that the vocalizations of brown-headed cowbirds, chipping sparrows, song sparrows, and yellow warblers were all distinctly different in structure, indicating that cowbird chicks do not mimic the vocalizations of their foster species. These results indicate that acceptance of the cowbird chick by the host is not dependent exclusively upon vocalizations.

Keywords: brood parasitism, host species, vocalization

Brown, B. T. 1994. Rates of brood parasitism by brown-headed cowbirds on riparian passerines in Arizona. J. Field Ornithol. 65:160-168.

Nests of brown-headed cowbird host species along the Colorado River within Grand Canyon National Park, Arizona, were monitored from 1982 to 1987 to evaluate host parasitism rates and to compare cowbird and host nesting chronology. Passerine hosts whose peak nesting coincided with peak cowbird nesting activity exhibited relatively high rates of brood parasitism.

Keywords: brood parasitism, host species, Arizona

Brunet, R. and J. McDuff. 1997. Recovery of brain cholinesterases of brown-headed cowbirds from organophosporus intoxication: effect of environmental temperature. Bull. Environ. Contam. Toxicol. 59:285-291.

The impact of ambient temperature on OPs toxicity was evaluated by monitoring the impact of a single dose of dimethoate on the brain AchE activity and the body temperature of brown-headed cowbirds at 5 and 25 ^oC over a 24-hour period. Results indicate cold temperature does not increase brain AchE inhibition, but rather slows down the rate of recovery; mortality can occur only a few hours after an exposure to OPs, especially at cold ambient temperatures.

Keywords: mortality

Buech, R. R. 1982. Nesting ecology and cowbird parasitism of clay-colored, chipping and field sparrows in a Christmas tree plantation. J. Field Ornithol. 53:363-369.

Brood parasitism by brown-headed cowbirds and nest site selection of clay-colored, chipping, and field sparrows in a Minnesota Scotch pine Christmas tree plantation in 1976 were evaluated.

Keywords: host species, nest-site selection, Minnesota

Bull, J. N. and J. W. McDaniel. 1976. The effect of food deprivation on status in a dominance hierarchy of the brown-headed cowbird (Molothrus ater). Jack-Pine Warbler 54:148-154.

This study investigated whether food deprivation affects the hierarchy within cowbird populations. It was predicted that a food-deprived bird would increase in dominance while a control bird with food access would remain stable in dominance; however, the deprived bird actually dropped in social rank during the experiments. It was suggested that the initial drop was due to debilitating effects of deprivation, while the continued drop was a result of learned subordination.

Keywords: social organization, diet

Burckley, M. 1995. Bosque birds. Quantum 12:5.

A summary of the population decline of the southwestern willow flycatcher, including threats of parasitism by the brown-headed cowbird.

Keywords: host species, brood parasitism

Burgham, M. C. J. 1985. The impact of brood parasitism by the brown-headed cowbird on the reproductive tactics of the yellow warbler. M.S. thesis, University of Ottawa, Ottawa.

Keywords: brood parasitism, host species

Burgham, M. C. J. and J. Picman. 1989. Effect of brown-headed cowbirds on the evolution of yellow warbler anti-parasite strategies. Anim. Behav. 38:298-308.

This study was designed to evaluate the impact of cowbird parasitism on the reproductive success of warblers relative to nest predation, and to determine whether warblers in eastern Ontario had evolved specific anti-parasite adaptations. The results suggest that parasitism accounted for 41% of all egg losses and was as important as nest predation. Warblers tended to reject cowbird eggs laid early in the egg-laying stage if enough time remained in the breeding season to attempt renesting. These findings suggest that warblers recognize brown-headed cowbirds as a specific threat to their nests.

Keywords: brood parasitism, host species

Burhans, D. E. 1997. Habitat and microhabitat features associated with cowbird parasitism in two forest edge cowbird hosts. Condor 99:866-872.

The author examined the relationship of habitat and brood parasitism by the brown-headed cowbird of field sparrows and indigo buntings in central Missouri. Results suggest that nest microhabitat features may influence the probability of parasitism. However, individual species and habitat characteristics may be more significant than microhabitat when estimating potential parasitism rates.

Keywords: habitat, Missouri

Burhans, D. E. and P. C. Freeman. 1997. Partial rejection of immaculate foreign eggs by yellow-breasted chats. Auk 114:503-506.

This study was designed to test whether yellow-breasted chats would eject dissimilar eggs more frequently than normal, maculated cowbird eggs in proportion to their divergence from their own eggs characteristics. They evaluated the response of chats when white-painted cowbird eggs and normal cowbird eggs were added to their nests. Chats ejected about half of the dissimilar eggs added to their nests and appeared to possess a coarse level of egg recognition. Recognition seemed to be based upon maculation rather than egg size.

Keywords: host defense, host species, egg manipulation

Burleigh, T. D. March 1936. Egg laying by the cowbird during migration. Wilson Bull. 48:13-16.

In 1934 a detailed study was conducted to ascertain the distribution and abundance of brown-headed cowbirds during the spring and summer in the vicinity of Asheville, North Carolina. Since cowbirds had not been documented in this area during the summer, it was of interest to find 2 red-eyed vireo nests in early June that had been parasitized, and by August, 12 young cowbirds had been observed, but no adults had been noted.

Keywords: brood parasitism, migration, North Carolina

Burnell, K. and S. I. Rothstein. 1994. Variation in the structure of female brown-headed cowbird vocalizations and its relation to vocal function and development. Condor 96:703-715.

Quantitative variation in frequency and temporal parameters were assessed by measuring 40 variables on female brown-headed cowbird chatter calls from 45 individuals from the three recognized subspecies. Univariate and multivariate analyses indicated only minor macrogeographic differences among the three subspecies and gave no indication that local microgeographic variation or dialects exist. Despite the near lack of spatial variation, analysis demonstrated that nearly every variable showed significant individual variation within the subspecies.

Keywords: vocalization

Burtt, H. E. and M. L. Glitz. 1976. Sex differences in the tendency for brown-headed cowbirds and red-winged blackbirds to re-enter a decoy trap. Ohio J. Sci. 76:264-267.

Using a decoy trap in an Ohio study from 1965-1974, female blackbirds and cowbirds were recaptured more frequently than males. Trap site selection was believed to be the major factor affecting the recapture rates of the female blackbirds and cowbirds. It is suggested that the females were more susceptible to the social stimulus provided by the decoy trap.

Keywords: trapping, behavior, Ohio

Byers, G. W. 1950. A black and white warblers nest with eight cowbird eggs. Wilson Bull. 62:136-138.

In 1949, the author observed a warblers nest with two host eggs and eight cowbird eggs in Wastenaw County, Michigan. Both host eggs were later ejected, either by the cowbird or by the host.

Keywords: host species, Michigan

Carey, C. 1986. Possible manipulation of eggshell conductance of host eggs by brown-headed cowbirds. Condor 88:388-390.

By pecking a hole in the shell of host species eggs, the cowbird can potentially reduce host competition. The purpose of this study was to determine the effect that the pecked hole has on eggshell water-vapor conductance and daily water loss to determine whether the hole increased rates of water loss beyond the limits lethal to the embryo. Results indicate that further study is necessary to clarify why a hole in the shell invariably leads to embryonic death. Since embryos invariably died in eggs with holes, the increase in the survival of cowbird offspring could possibly lead to an evolutionary prevalence of this phenomenon in the future.

Keywords: eggs, brood parasitism

Carter, M. D. 1984. The social organization and parasitic behavior of the bronzed cowbird in south Texas. Ph.D. diss., University of Minnesota, Morris.

During early April to mid-July of 1980-1981 and mid-April to mid-August of 1982, data were gathered on various aspects of the breeding ecology of the bronzed cowbird on the Santa Ana National Wildlife Refuge in southern Texas. Data included parasitic habits, possible adult and nestling adaptations for parasitism, and anti-parasite strategies used by several hosts.

Keywords: bronzed cowbird, host defense, host species, Texas

Carter, M. D. 1986. The parasitic behavior of the bronzed cowbird in south Texas. Condor 88:11-25.

The breeding ecology of the bronzed cowbird was studied from 1980 to 1982 at the Santa Ana National Wildlife Refuge in southern Texas. Cowbird nestlings possess no apparent special adaptation for brood parasitism. However, their loud vocal nature appears to give them a competitive edge against less vocal host nestmates.

Keywords: bronzed cowbird, brood parasitism, Texas

Cavalcanti, R. B. and T. M. Pimentel. 1988. Shiny cowbird parasitism in central Brazil. Condor 90:40-43.

Between September and December of 1982 to 1984, the authors observed cowbird nestlings or fledglings being fed by the adults of six different species. The authors artificially parasitized fork-tailed flycatcher nests, and suggest that in Brasilia, flycatchers may accept cowbird eggs placed during incubation.

Keywords: shiny cowbird, host species, Brazil

Chace, J. F., A. Cruz, and R. E. Marvil. 1994. The impact of brood parasitism on the reproductive success of the solitary vireo. J. Colorado-Wyoming Acad. Sci. 26:34.

A 10-year study was conducted to examine the reproductive success of the solitary vireo in the ponderosa pine forests of Boulder County, Colorado. A total of 117 nests were monitored from the egg laying stage through fledging during the years of 1984, 1985, 1986, 1992, and 1993. Nest predation and brood parasitism were the two most important factors influencing reproductive success.

Keywords: brood parasitism, Colorado

Chace, J. F. 1995. Further information on the obscurus race of the brown-headed cowbird in Colorado. C.F.O. Journal 29:146-148.

Three obscurus specimens were collected in Boulder County during 1984 and 1986, which indicate a recent range expansion of the subspecies into northern Colorado. The specimens are housed at the University of Colorado Museum.

Keywords: range expansion, Colorado

Chace, J. F. and A. Cruz. 1996. Knowledge of the Colorado host relations of the parasitic brown-headed cowbird (Molothrus ater). C.F.O. Journal 30:67-81.

The authors reviewed existing literature and added new species to the list of potential cowbird hosts in Colorado. New information has been gathered from the Nest Record Card Program, observer reports from the Colorado Breeding Bird Atlas, egg collections from the University of Colorado Museum and Denver Museum of Natural History, and field observations. This compilation of Colorado parasitism records documents changes in host species selection by the brown-headed cowbird and provides baseline knowledge of their host relationships in Colorado.

Keywords: host species, Colorado

Chace, J. F., A. Cruz, and A. Cruz, Jr. 1997. Nesting success of the western wood-pewee in Colorado. Western Birds 28:110-112.

In 1990 and 1992, none of the 26 western wood-pewee nests were parasitized by the brown-headed cowbird, however within the same study area 47% of solitary vireo nests were parasitized in 1984, 1985, 1986, 1992, and 1993.

Keywords: host species, brood parasitism, Colorado

Chace, J.F. and A. Cruz. 1998. Range of the brown-headed cowbird in Colorado: past and present. Great Basin Naturalist 58:245-249.

In this report the authors suggest that high-elevation breeding songbirds in Colorado have maintained a long-term host-parasite relationship with the brown-headed cowbird. Based on the historic commensal relationship of cowbirds and bison, the cowbird is believed to have established a historical elevational range higher than previously believed.

Keywords: range expansion, Colorado

Cichon, M. 1996. The evolution of brood parasitism: the role of facultative parasitism. Behav. Ecol. 7:137-139.

This report investigates the hypothesis that facultative brood parasitism may serve as an intermediate step in the evolutionary transition from purely parental reproduction to obligate parasitism. A computerized model was developed to evaluate the population dynamics of a host-parasite complex using various intensities of parasitism rates and host defenses. The results indicate that a host population that demonstrates a particular degree of defense can sustain a certain level of parasitism and that a stable coexistence of hosts and parasites is possible.

Keywords: brood parasitism, model

Clark, K. L. and R. J. Robertson. 1981. Cowbird parasitism and evolution of anti-parasite strategies in the yellow warbler. Wilson Bull. 93:249-258.

The behavioral response of nesting yellow warblers to naturally laid brown-headed cowbird eggs was documented with the acceptance of cowbird eggs resulting in a significantly lower nest success for warblers. The most frequent behavioral response by the warbler was the burial of cowbird eggs. Parasitized nests in which burial occurred had success rates comparable to unparasitized nests.

Keywords: host defense, host species

Clark, L. and J. R. Mason. 1989. Sensitivity of brown-headed cowbirds to volatiles. Condor 91:922-932.

Brown-headed cowbirds were studied to determine their ability to discriminate between two odors, ethyl butyrate and s-limonene, using a cardiac conditioning paradigm. Cowbirds also were able to discriminate among concentrations of ethyl butyrate. Although passerines are presumed to have poor olfactory abilities, the sensitivity values were within the same range as those found in nonpasserines that have more developed olfactory anatomies.

Keywords: olfaction

Clotfelter, E. D. 1997. Red-winged blackbird parental investment following brood parasitism by brown-headed cowbirds: is parentage important? Behav. Ecol. Sociobiol. 41:193-201.

The parental behavior of red-winged blackbirds in response to natural and experimental brown-headed cowbird parasitism and in response to a freeze-dried female cowbird placed in close proximity of their nest was recorded. Parental investment was measured by the degree of nest defense toward a model predator, and by the feeding rate of nestlings. No significant differences in levels of parental investment among unparasitized nests, naturally parasitized nests, or experimentally parasitized nests were recorded.

Keywords: host defense, host species

Clotfelter, E. D. 1995. Courtship displaying and intra sexual competition in the bronzed cowbird. Condor 97:816-818.

In this study the author recorded the observations of bronzed cowbird courtship behavior to test predictions regarding mate choice and intrasexual competition. Observations were made at the Santa Ana National Wildlife Refuge, Hidalgo County, Texas, during June and July 1994.

Keywords: bronzed cowbird, mate selection, Texas

Clotfelter, E. D. and T. Brush. 1995. Unusual parasitism by the bronzed cowbird. Condor 97:814-815.

The authors report four unusual incidences of brood parasitism by the bronzed cowbird in south Texas during July 1993 and June-July 1994, which include: (1) the first reported use of the yellow-billed cuckoo as a host; (2) the first reported use of the western kingbird as a host; (3) the second reported raising of bronzed cowbirds to fledging age by a Couchs kingbird, a known rejector of cowbird eggs; and (4) a record number of parasitic eggs laid in a single hosts nest and still incubated by the host, in this case a green jay.

Keywords: bronzed cowbird, host species, Texas

Coker, D. R. and J. L. Confer. 1990. Brown-headed cowbird parasitism on golden-winged and blue-winged warblers. Wilson Bull. 102:550-552.

This article summarizes the decline of golden-winged and blue-winged warblers in New York. Analyses of this large data set suggest that the influence of the cowbird on both species is very similar and that parasitism by the cowbird has contributed to their decline.

Keywords: brood parasitism, range expansion, New York

Coker, D. R. and D. E. Capen. 1995. Landscape-level habitat use by brown-headed cowbirds in Vermont. J. Wildl. Manage. 59:631-637.

The authors conducted a study within a forested habitat of central Vermont in an attempt to evaluate the relationship between forest disturbance and the distribution of the brown-headed cowbird in New England. Sixty-seven randomly selected areas from a total of 702 areas where disturbance had created permanent openings, such as pastures, lawns, and ski areas, and where recent logging had created temporary forest openings, were surveyed during the 1992-1993 breeding seasons. Cowbirds were detected in 46% of the surveyed patches.

Keywords: habitat, range expansion, Vermont

Collins, C. T., D. F. Tomback, and G. E. Woolfenden. 1980. Additional host records for the bronzed cowbird in Texas. Bull. Texas Ornithol. Soc. 13:50-51.

The author provides a summary of previously unrecorded accounts of host species rearing cowbird young in the Rio Grande Valley, Hidalgo County, Texas, in August of 1979.

Keywords: bronzed cowbird, host species, Texas

Coon, D. W. and K. A. Arnold. 1977. Origins of brown-headed cowbird populations wintering in central Texas. N. Amer. Bird Bander 2:7-11.

Banding returns from over 60,000 banded brown-headed cowbirds from 1969-1974 and 1932-1968 are presented. Banding results concentrate on encounters of cowbirds banded during the winter in Texas and on all Texas encounters of birds banded in other states.

Keywords: band recovery, range expansion, Texas

Coues, E. 1884. Egg of the cowbird in nest of the Carolina dove. Auk 1:293.

This report includes the Carolina dove to the list of potential host species. The Carolina dove is the largest bird known to be chosen as the cowbirds foster-parent.

Keywords: host species

Crase, F. T., R. W. DeHaven, and P. P. Woronecki. 1972. Movements of brown-headed cowbirds banded in the Sacramento Valley, California. Bird-Banding 43:197-204.

Brown-headed cowbird movements are presented for 67 banded recoveries and 87 banded returns from 16,165 individuals banded from 1964 through 1971 near Colusa, Colusa County, California. The distribution of in-state banded recoveries indicates that cowbirds are present year-round, and there is only subtle southern movements from Colusa. Approximately one-half of the April-September banded recoveries of cowbirds at Colusa were north of California, which is a result of the spring migration. In the fall, cowbirds tend to concentrate in the northern Sacramento Valley; many of the same individuals apparently return to this area annually.

Keywords: band recovery, movements, California

Crook, C. 1934. Cowbird notes from Tennessee. Auk 51:384-385.

A first-person account reporting the discovery of a cowbird egg in the nest of a Carolina wren in 1933.

Keywords: host species, Tennessee

Cross, F. C. 1950. Virginia warbler parasitized by cowbird. Condor 52:138.

A first-person account of the first recorded observation of cowbird parasitism on the Virginia warbler near Denver, Colorado, in 1949.

Keywords: host species, Colorado

Cruz, A. C., J. W. Wiley, T. K. Nakamura, and W. Post. 1989. The shiny cowbird Molothrus bonariensis in the West Indian Region - biographical and ecological implications. Pages (unknown) in C. A. Woods (ed.). Biogeography of the West Indies. Brill, Leiden, Neth.

Keywords: shiny cowbird, brood parasitism

Cruz, A. and J. W. Wiley. 1989. The decline of an adaptation in the absence of a presumed selection pressure. Evolution 43:55-62.

The authors report a case involving the decline of a discrete adaptation in response to removal of a selection pressure: a decrease of egg-ejection behavior in the village weaver in the absence of brood parasitism.

Keywords: shiny cowbird, brood parasitism, evolution

Cruz, A., T. Manolis, and J. W. Wiley. 1985. The shiny cowbird: a brood parasite expanding its range in the Caribbean region. Ornithol. Monog. 36:607-620.

The relationship between the shiny cowbird and the yellow-hooded blackbird in Trinidad, an area of long parasite-host interaction, is compared with the relationship between the cowbird and the yellow-shouldered blackbird in Puerto Rico, an area of recent cowbird-host interaction.

Keywords: shiny cowbird, range expansion, Trinidad, West Indies, Puerto Rico

Cruz, A., T. D. Manolis, and R. W. Andrews. 1990. Reproductive interactions of the shiny cowbird Molothrus bonariensis and the yellow-hooded blackbird Agelaius icterocephalus in Trinidad. Ibis 132:436-444.

The reproductive interactions of the shiny cowbird and the yellow-hooded blackbird were studied in Trinidad, West Indies, from 1979 to 1981, and in 1984. The authors studied the breeding biology of the shiny cowbird and the yellow-hooded blackbird to determine the parasitism rates and the effects of brood parasitism on host breeding success.

Keywords: shiny cowbird, brood parasitism, Trinidad, West Indies

Cruz, A., T. H. Manolis, and R. W. Andrews. 1995. History of shiny cowbird Molothrus bonariensis brood parasitism in Trinidad and Tobago. Ibis 137:317-321.

The authors evaluated cowbird-host interaction in Trinidad and Tobago based on extensive literature reviews, and personal communications with individuals knowledgeable of the avifauna in Trinidad and Tobago. Between 1979 and 1981 and in 1984, the authors gathered information on the breeding biology of shiny cowbirds, host species, and parasitism rates.

Keywords: shiny cowbird, brood parasitism, host species, Tobago, Trinidad, West Indies

Cruz, A. and R. W. Andrews. 1997. The breeding biology of the pied water-tyrant and its interactions with the shiny cowbird in Venezuela. J. Field Ornithol. 68:91-97.

The authors study the breeding biology of the water-tyrant in a seasonally inundated savanna in the llanos of western Venezuela. Some 123 nests were located during the wet season of June-October 1982 and 1983. Data on parasitism rates, number of eggs per nest, and number of host fledglings are presented. The pied water-tyrant does not appear to be an optimal host for the shiny cowbird since only 3 of 47 parasitized nests were known to have successfully fledged cowbird young.

Keywords: shiny cowbird, brood parasitism, host species, Venezuela

Darley, J. A. 1968. The social organization of breeding brown-headed cowbirds. Ph.D. diss., University of Western Ontario, London.

Keywords: social organization

Darley, J. A. 1971. Sex ratio and mortality in the brown-headed cowbird. Auk 88:560-566.

This paper presents sex ratio, age, and mortality data from a population of breeding brown-headed cowbirds. The results support earlier reports of excess males by Friedmann (1929) and McIlhenny (1940). This report constitutes only a portion of a more extensive study on the social organization of breeding cowbirds.

Keywords: mortality, sex ratio, social organization

Darley, J. A. 1978. Pairing in captive brown-headed cowbirds (Molothrus ater). Can. J. Zool. 56:2249-2252.

Twenty-five male and 15 female cowbirds were captured in the fall of 1966. In mid-December of 1966, they were subjected to an extended photoperiod to bring them into breeding condition. Various combinations of yearling and adult males and females were observed in eight trials to determine the effect of age and social dominance of males on pairing with females. Age did not appear to be a factor in pairing, however only dominant males paired with females. Subordinate males did not pair when an insufficient number of females were available. These results confirm the opinions developed through field observations on the role of dominance and age in the pairing of brown-headed cowbirds.

Keywords: behavior

Darley, J. A. 1982. Territoriality and mating behavior of the male brown-headed cowbird. Condor 84:15-21.

The social behavior of 154 banded male cowbirds was studied at London, Ontario, in 1966 and 1967. Aggressive encounters between the males appeared to involve either the establishment and maintenance of a dominance hierarchy or the guarding of resident females. Dominant males that paired with females maintained primarily monogamous relationships. Although males may occupy a specific range, there was no evidence of territorial defense, however dominant males did defend their females. Females, at times, also defended their males from other females. Excess males that were present and in breeding condition attended any female during her mates absence, courting and guarding her from advances by other males and occasionally copulating with her.

Keywords: mating system, social organization, territorial behavior, Ontario, Canada

Darley, J. A. 1983. Territorial behavior of the female brown-headed cowbird (Molothrus ater). Can. J. Zool. 61:65-69.

The territorial behavior of the female brown-headed cowbird was studied at London, Ontario, in 1966 and 1967. Cowbirds arrived in the study area during the last week of March and the first 2 weeks of April. Adult birds arrived about 2 weeks before the yearlings. Forty-six resident and 56 nonresident females were observed in the study area; the nonresidents appeared to use the area for feeding. The breeding residents established home ranges mainly through the use of threat displays. The defense of these home ranges suggests that they might be classified as territories. Thirty-nine breeding resident females, 17 yearlings, and 22 adults had home ranges ranging from 0.9 to 13.4 ha (average 4.5 +/- 0.4 ha).

Keywords: territorial behavior, Ontario, Canada

Davis, D. E. 1942. The number of eggs laid by cowbirds. Condor 44:10-12.

In this study, the author was unable to determine the oviposition in cowbirds due to inherent difficulties of studying a parasitic bird based on available literature. However, by utilizing several techniques, the author was able to tentatively determine the number of eggs laid by an individual cowbird. Other data suggest that four species of cowbirds (Agelaioides badius, Molothrus rufo-axillaris, M. bonariensis, and M. ater) lay eggs in clutches of four or five.

Keywords: fecundity, laying rate

Dearborn, D. C. 1996. Video documentation of a brown-headed cowbird nestling ejecting an indigo bunting nestling from the nest. Condor 98:645-649.

This paper presents the first video documentation of a cowbird nestling ejecting a host nestling from the nest. A 25-second video segment of this activity can be viewed at http://server1.biosci.missouri.edu/dearborn/cowbird.html.

Keywords: behavior

Dearborn, D. C. and A. D. Anders. 1998. Effects of cowbird parasitism on parental provisioning and nestling food acquisition and growth. Condor 100:326-334.

The authors studied nestling growth, food acquisition, and parental provisioning in parasitized and unparasitized nests of the indigo bunting. The study also suggests that conservation measures should not focus strictly on host species that suffer total reproductive failure since brood parasitism appears to significantly reduce the reproductive potential of other neotropical migrants as well.

Keywords: growth rate, brood parasitism

Debrot, A. O. and T. K. Prins. 1992. First record and establishment of the shiny cowbird in Curacao. Caribbean J. Sci. 28:104-105.

The authors report the first record of shiny cowbird in the Netherlands Antilles in 1991. From March 8 through May 12, 1991, 13 specimens were collected near Soto, Girouette, and Jan Sofat, on the island of Curacao.

Keywords: shiny cowbird, range expansion, Curacao

DeCapita, M. E. 1991. Control of brown-headed cowbirds on Kirtlands warbler nesting area in northern Michigan - 1991. U.S. Fish and Wildlife Service Report. East Lansing, Michigan.

Keywords: brood parasitism, host species, population control, trapping, Michigan

Decapita, M. E. 1993. Control of brown-headed cowbirds on Kirtlands warbler nesting areas in northern Michigan - 1992. U.S. Fish and Wildlife Service Report. East Lansing, Michigan.

Keywords: brood parasitism, host species, population control, trapping, Michigan

De Geus, D. W. 1991. Brown-headed cowbirds parasitize loggerhead shrikes: first records for family Laniidae. Wilson Bull. 103:504-506.

This report documents the first record of cowbird parasitism on the loggerhead shrike. It also documents the first account of shrikes rearing cowbird young from eggs deposited by cowbirds in southwestern Iowa in 1988.

Keywords: brood parasitism, host species, Iowa

Denton, J. F. 1946. A further note on the breeding of the cowbird in Richmond County. Oriole 11:24-27.

Adds the brown-headed cowbird to the list of breeding birds in Georgia.

Keywords: range expansion, Georgia

Denton, J. F. 1958. A further note on the breeding of the cowbird in Richmond County (Georgia). Oriole 23:37-38.

A first-person account of further observations of cowbirds and of brood parasitism in Georgia since 1946.

Keywords: brood parasitism, host species, Georgia

Dickerman, R. W. 1960. Red-eyed cowbird parasitizes song sparrow and Mexican cacique. Auk 77:472-473.

The author reports the first record of red-eyed cowbird parasitism of the song sparrow and Mexican cacique.

Keywords: bronzed cowbird, host species

Dolan, P. M. and P. L. Wright. 1984. Damaged western flycatcher eggs in nests containing brown-headed cowbird chicks. Condor 86:483-485.

The authors document the damage of western flycatcher eggs near Missoula, Montana, from a nest containing cowbird chicks. They describe the incidence and extent of the damage to the flycatcher eggs, and consider several hypotheses concerning its cause.

Keywords: brood parasitism, host species, Montana

Dolbeer, R. A., P. P. Woronecki, A. R. Stickley, Jr., and S. B. White. 1978. Agricultural impact of a winter population of blackbirds and starlings. Wilson Bull. 90:31-44.

During the winter of 1975-1976 the habitat preferences and use, food habits, and impact on agriculture of 11 million blackbirds and starlings wintering in Gibson County, Tennessee, were assessed. The winter roost was composed of common grackles (64%), red-winged blackbirds and brown-headed cowbirds (27%), starlings (9%), and rusty blackbirds (<1%). Cowbirds and starlings commonly used pastures and feedlots.

Keywords: diet, habitat, Tennessee

Dolbeer, R. A. and R. A. Stehn. 1979. Population trends of blackbirds and starlings in North America, 1966-76. USFWS, Spec. Sci. Rep. Wildl. 214.

Keywords: distribution

Dolbeer, R. A. 1982. Migration patterns for age and sex classes of blackbirds and starlings. J. Field Ornithol. 53:28-46.

The movements of red-winged blackbirds, brown-headed cowbirds, and starlings from one breeding season to subsequent breeding seasons were studied. Dispersal and migration patterns based on age and sex classes, and the timing and distances of migration from the nesting area to the wintering area were evaluated to gain insight into the degree of intermingling of populations at winter roost sites.

Keywords: migration

Dolbeer, R. A. and R. A. Stehn. 1983. Population status of blackbirds and starlings in North America, 1966-81. Proc. Eastern Wildl. Dam. Control Conf., Cornell University, Ithaca, New York 1:51-61.

Based on 16 years of Breeding Bird Survey data, population trends are examined. The Upper Great Plains and the Southeastern United States have experienced the greatest increase in cowbird populations. Population declines were found from central Michigan to Minnesota.

Keywords: range expansion, distribution

Dolbeer, R. A. and C. R. Smith. 1985. Sex-specific feeding habits of brown-headed cowbirds in northern Ohio in January. Ohio J. Sci. 85:104-107.

The authors examined the stomach contents of 57 brown-headed cowbirds collected from a roost in Erie County, Ohio, on January 12, 1983. Corn comprised 66% of the stomach contents by weight. Grass seed from at least five species accounted for 21% of the stomach contents, while ragweed constituted 2.6% contents by weight. Male cowbirds consumed more corn than females, whereas females consumed more of the smaller grass seeds. The abundance of corn in harvested fields and feedlots, combined with mild winter conditions, was the primary reason cowbirds were able to overwinter several hundred kilometers north of their usual winter range.

Keywords: diet, migration, Ohio

Donovan, T. M., P. W. Jones, E. M. Annand, and F. R. Thompson III. 1997. Variation in local-scale edge effects: mechanisms and landscape context. Ecology 78:2064-2075.

Nest predation and cowbird distribution within forest edge and forest interior habitats over 36 randomly selected plots covering three Midwestern States were assessed. The authors constructed artificial nests and baited them with quail and clay eggs to observe both predators and predation patterns. Point counts were also conducted to determine cowbird and host abundance in both forest edge and forest interior habitats. When predicting impacts on the reproductive success of forest songbirds, the authors suggest assessing habitat characteristics on a landscape level.

Keywords: habitat, egg manipulation

Dow, D. D. 1968. Allopreening invitation display of a brown-headed cowbird to cardinals under natural conditions. Wilson Bull. 80:494-495.

A first-person observation documenting a female cowbird displaying a preening invitation to a female cardinal in 1966 in Weakley County, Tennessee.

Keywords: behavior, Tennessee

Dufour, K. W. and P. J. Weatherhead. 1991. A test of the condition-bias hypothesis using brown-headed cowbirds trapped during the breeding season. Can. J. Zool. 69:2686-2692

. During the 1987 and 1988 breeding seasons, cowbirds used as decoys were examined to determine if trapping efforts are bias relative to body condition, age, and sex. Decoy-trapped birds of both sexes were in poor condition relative to those captured by mist netting. Trapping was strongly male biased, which likely reflects a difference in the males nutritional requirements and foraging strategies. These results indicate that trapping efforts relying on a feeding response (i.e., bait) as an attractant, will likely bias the capture rates and interpretation of these data should be conducted with caution.

Keywords: sex ratio, trapping

Dufty, A. M. Jr. 1981. Social organization of the brown-headed cowbird, Molothrus ater, in New York State. Ph.D. diss. State University of New York at Binghamton.

Radiotelemetry and tape-playback of conspecific vocalizations were used to evaluate cowbird movements and their breeding behavior. Radio tracking indicated monogamous pairing, and that each pair maintained a well-defined nonfeeding range. Tape-playback results supported those of the radio tracking. This study indicates that cowbirds found in New York State during the breeding season form monogamous pairs, the male defends his female from other males, and females defend their nonfeeding ranges.

Keywords: behavior, mating system, social organization, territorial behavior, radio telemetry, New York

Dufty, A. M. Jr. 1982. Response of brown-headed cowbirds to simulated conspecific intruders. Anim. Behav. 30:1043-1052.

The response of brown-headed cowbirds to simulated intruders was examined using playback of cowbird vocalizations in conjunction with a model of a male or female cowbird. While females reacted aggressively towards female vocalizations, they did not react toward male vocalizations. Solitary males approached, and often courted the female model, but did not approach the male model. Males with accompanying females, reacted little to the models of either sex. The results of the study support the hypothesis that female cowbirds are territorial and that males guard females from the solicitation of other males. The ecological pressures which may have influenced the development of this social system are also discussed.

Keywords: behavior, mating system, territorial behavior

Dufty, A. M. Jr. 1982. Movements and activities of radio-tracked brown-headed cowbirds. Auk 99:316-327.

The social organization of a color-marked cowbird population was investigated during the 1978-1980 breeding seasons. Several individuals from the local population were radio-tracked, some during more than one season. Monogamous relationships were documented with each pair maintaining a relatively large nonfeeding range. Females appeared to defend their nonfeeding ranges from other females, and males guarded females from other males. Most cowbird pairs that returned in successive years exhibited mate and site fidelity, however mate fidelity may be a coincidental result of site fidelity.

Keywords: movements, social organization, territorial behavior, radio telemetry

Dufty, A. M. Jr. 1983. Variation in the egg markings of the brown-headed cowbird. Condor 85:109-111.

Four pair of brown-headed cowbird eggs, laid by four individual females, were collected and presented to human subjects to test their abilities to differentiate between the eggs and match the four pair correctly. The results discuss the subjects ability to match the pairs based only on appearance.

Keywords: eggs

Dufty, A. M. Jr. 1985. Song sharing in the brown-headed cowbird (Molothrus ater). Z. Tierpsychol. 69:177-190.

Songs from two separate populations of cowbirds near Binghamton, New York, and in Millbrook, New York, were recorded and compared. In most cases, songs were similar between the two populations; however, in one population, paired males exhibited more song types than did the remainder of the population. Song learning, in conjunction with low dispersal, is believed to contribute to song sharing in this species.

Keywords: vocalization, New York

Dufty, A. M. Jr. 1986. Singing and the establishment and maintenance of dominance hierarchies in captive brown-headed cowbirds. Behav. Ecol. Sociobiol. 19:49-55.

Three males and one female brown-headed cowbird from captive flocks were studied to evaluate the importance of singing when establishing and maintaining social dominance. In one experiment, the two larger males within each of four flocks were temporarily devocalized by puncturing the interclavicular air sac prior to group formation. Results conclude there was a significant tendency for the nondevocalized birds to become the dominant member of their group. However, in a subsequent experiment, dominant males from flocks with established hierarchies that were temporarily devocalized did not lose their dominant positions.

Keywords: social organization, vocalization

Dufty, A. M. Jr. and J. C. Wingfield. 1986. The influence of social cues on the reproductive endocrinology of male brown-headed cowbirds: field and laboratory studies. Hormones and Behavior 20:222-234.

Article presents results of a testosterone level study that suggest social stimuli are important in modulating the secretion of testosterone in males early in the season when pairing occurs, and possibly late in the season as well.

Keywords: endocrinology

Dufty, A. M. Jr. and J. C. Wingfield. 1986. Temporal patterns of circulating LH and steroid hormones in a brood parasite, the brown-headed cowbird, Molothrus ater. I. Males. J. Zool., Lond. 208:191-203.

This report describes endocrine changes in the plasma of free-living brown-headed cowbirds during a breeding season. Changes in some morphological parameters are also presented. Circulating levels of corticosterone are elevated until the middle of the breeding season, when they begin to fall, although there is a transient depression just prior to breeding. These data suggest that hormone profiles are closely correlated with the breeding and social activities that characterize this species.

Keywords: endocrinology, morphology

Dufty, A. M. Jr. and J. C. Wingfield. 1986. Temporal patterns of circulating LH and steroid hormones in a brood parasite, the brown-headed cowbird, Molothrus ater. II. Females. J. Zool., Lond. 208:205-214.

This article reports the changes in plasma levels of circulating hormones and in morphological characteristics that occur in free-living female cowbirds throughout the breeding season. Fat scores in females were the highest prior to egg laying, and diminished throughout the breeding season. In contrast, body weight increased during the breeding season, which is likely a result of the developing eggs in the ovary. These results support the hypothesis that temporal patterns of hormone secretion are correlated with the expression of social systems.

Keywords: endocrinology

Dufty, A. M. Jr., A. R. Goldsmith, and J. C. Wingfield. 1987. Prolactin secretion in a brood parasite, the brown-headed cowbird, Molothrus ater. J. Zool. Lond. 212:669-675.

Blood samples of male and female brown-headed cowbirds were collected from a New York population during the breeding season. Plasma levels of prolactin were measured by radioimmunoassay. The level of prolactin peaked by June and were maintained into July. Prolactin levels in juveniles were significantly lower than in adults but were still elevated. Prolactin has been correlated to parental care in several avian species. However, it is believed that prolactin must either serve an alternative function in cowbirds or they have become insensitive to the hormone, since cowbirds are brood parasites and exhibit no parental behavior.

Keywords: endocrinology, behavior

Dufty, A. M. Jr. 1988. Flight whistle incorporated in brown-headed cowbird song. Condor 90:508-510.

A summary of cowbird vocalizations, including distinction between songs and calls.

Keywords: vocalization

Dufty, A. M. Jr. 1988. The effects of repeated blood sampling on survival in brown-headed cowbirds. Condor 90:939-941.

Study determined the effect of repeated blood sampling on survival based on data collected during a 6-year study of brown-headed cowbirds. Results suggest that females are more susceptible than males to the adverse effects of multiple blood sampling, which results in a reduction of blood volume and hematocrit.

Keywords: mortality

Dufty, A. M. Jr. 1989. Testosterone and survival: a cost of aggressiveness? Hormones and Behavior 23:185-193.

Male brown-headed cowbirds were captured during the breeding season, implanted with testosterone-filled Silastic tubing, and released to compare the survival between implanted males, unimplanted males captured in previous years, and males that were given empty implants. Androgen-implanted males exhibited significantly reduced survival to the following year compared with either of the control groups. The implanted males also exhibited severe injuries which had not been documented previously. The study results suggest that the increased risks associated with prolonged high testosterone levels act as a selective force to maintain reduced androgen levels, except during the period of aggressive intrasexual interactions that occur during the breeding season.

Keywords: endocrinology

Dufty, A. M. Jr. and J. C. Wingfield. 1990. Endocrine response of captive male brown-headed cowbirds to intra sexual social cues. Condor 92:613-620.

The hormonal response to a spectrum of intrasexual social stimuli was studied in captive cowbirds by placing males in cages and subjecting them to various combinations of visual and vocal stimuli. Blood samples were taken at 2-week intervals throughout the spring and early summer and evaluated for testosterone levels. The greatest increase in testosterone was in the birds that were subjected to both visual and vocal stimuli, and in those receiving only visual stimuli. The males that were subjected only to vocal stimuli experienced a muted endocrine response, and those receiving no social stimulation exhibited the briefest response.

Keywords: vocalization, endocrinology

Dufty, A. M. Jr. and R. McChrystal. 1992. Vocalizations and copulatory attempts in free-living brown-headed cowbirds. J. Field Ornithol. 63:16-25.

Audio spectrograms of male brown-headed cowbird vocalizations were recorded during 12 copulatory attempts. Incorporation of flight whistles during copulatory attempts may reflect conflicting tendencies during times of heightened sexual stimuli. However, flight whistles may have a direct stimulatory effect on the females willingness to mate.

Keywords: vocalization

Dufty, A. M. 1993. Testosterone concentrations in males of an atypical species: the brood parasitic brown-headed cowbird. Pages 61-72 in P. J. Sharp (ed.). Avian endocrinology. J. Endocrinology, Ltd. Bristol.

The objectives of this study were to evaluate the relationship between concentrations of plasma testosterone and reproductive and accompanying social behaviors in the brown-headed cowbird. Interesting comparative results between cowbirds and other species were found, and recommendations for future studies were discussed.

Keywords: behavior, endocrinology

Dufty, A. M. Jr. and J. K. Pugh. 1994. Response of male brown-headed cowbirds to broadcast of complete or partial flight whistles. Auk 11:734-739.

In 1990, near Boise, Idaho, the vocal and behavioral responses of male cowbirds to broadcasted tape recordings of the first half, second half, or full flight whistle were documented. The authors tested the hypothesis that perched male cowbirds respond to partial flight whistles by producing the missing whistle section. The results suggest that male cowbirds interact in a leader-follower manner, using a nonsong vocalization.

Keywords: vocalization

Earley, C. G. 1991. Brown-headed cowbird, Molothrus ater, seen removing a chipping sparrow, Spizella passerina, egg. Can. Field-Nat. 105:281-282.

This report documents the removal of a chipping sparrow egg from its nest by a female brown-headed cowbird. The event represents the latest time of day a cowbird has been observed removing an egg from the host species nest. Results suggest that the time of egg removal may be linked to whether or not the hosts nesting habitat is the same as the cowbirds feeding habitat.

Keywords: brood parasitism, host species

Eastzer, D., P. R. Chu, and A. P. King. 1980. The young cowbird: average or optimal nestling? Condor 82:417-425.

This study was conducted to determine whether hatching success and survival of brown-headed cowbird eggs and chicks were higher than those of nonparasitic passerines. Eggs and nestlings of seven species were placed in barn swallow and house sparrow nests and hatching success and nestling survival rates were compared. The young cowbird fared no better than the other species as a nestling. Although cowbirds can be reared by their most frequent host species, they may not be particularly successful with some of their less common hosts.

Keywords: brood parasitism, host species

Eastzer, D. H., A. P. King, and M. J. West. 1985. Patterns of courtship between cowbird subspecies: evidence for positive assortment. Anim. Behav. 33:30-39.

The author observed the courtship and mating behavior of captive individuals from allopatric populations of two brown-headed cowbird subspecies (M. a. ater and M. a. obscurus obscurus) by placing them within a indoor-outdoor aviary and using a multiple-choice design to assess whether individuals would selectively pair with members of their own subspecies. Individuals tended to pair with consubspecifics whether or not they had prior breeding experience with consubspecifics or winter contact with heterosubspecifics. This demonstration of selective courtship between individuals of widely separated populations is believed to be one of the first quantified examples of the development of assortative pairing in allopatry for a passerine species. These data, and supporting studies, suggest that the females preferential response to the song of her subspecies may play an important role for selective mating between passerine populations.

Keywords: behavior, vocalization

Eckerle, K. P. and R. Breitwisch. 1997. Reproductive success of the northern cardinal, a large host of brown-headed cowbirds. Condor 99:169-178.

The authors investigated the effects of brood parasitism by cowbirds on cardinal reproductive success to test the hypothesis that cowbird hosts of similar size and incubation period are able to raise their own offspring when parasitized. During the breeding seasons of 1993-1995, they collected data on the frequency and intensity of cowbird parasitism, the effect of cowbird parasitism on cardinal reproductive success, and the defensive response of cardinals to parasitism. These data suggest that this population of cardinals does not significantly suffer when parasitism occurs, which may explain the lack of defensive response.

Keywords: brood parasitism, host defense, host species

Elder, H. E. 1921. The cowbird: a parasite. Bird-Lore 23:185-191.

This paper is based upon observations of brood parasitism made in the vicinity of Winona Lake, between June 14 and August 20, 1920. These observations were an attempt to better understand the life history of the brown-headed cowbird.

Keywords: brood parasitism, host species, life history

Elliott, P. F. 1977. Adaptive significance of cowbird egg distribution. Auk 94:590-593.

During 1974 and 1975 in the Flint Hills of northeastern Kansas, the author studied brood parasitism by the brown-headed cowbird on three prairie, ground-nesting species: the grasshopper sparrow, the dickcissel, and the eastern meadowlark. Evidence suggests that cowbird egg distribution is nonrandom. Possible advantages of this behavioral pattern may be related to minimizing mistaken ejections by female cowbirds.

Keywords: behavior, brood parasitism, host species, Kansas

Elliott, P. F. 1978. Cowbird parasitism in the Kansas tallgrass prairie. Auk 95:161-167.

During 1974 and 1975, brood parasitism by the brown-headed cowbird was studied in a tallgrass prairie community in northeastern Kansas. A total of 77 nests of the three ground-nesting species were discovered, of which 54 (70.1%) were parasitized. A high intensity of brood parasitism is indicative of high relative densities of cowbirds. In this system, nesting success of nine species was very low, suggesting that the high densities of cowbirds were due to high adult survival. The implications of this situation are discussed.

Keywords: brood parasitism, host species, Kansas

Elliott, P. F. 1980. Evolution of promiscuity in the brown-headed cowbird. Condor 82:138-141.

A study of the social behavior of cowbirds from 1974 to 1975 suggests that in prairie communities the predominant mating behavior is promiscuous. Individuals of both sexes were marked and observed copulating with more than one individual, suggesting that long-term pair bonds were nonexistent. Since the cowbirds foraged with grazing cattle, which serves as a moving resource, it was hypothesized that this relationship with cattle selects against the evolution of territorial behavior, and for the evolution of promiscuity.

Keywords: mating system

Evans, D. R. and J. E. Gates. 1997. Cowbird selection of breeding areas: the role of habitat and bird species abundance. Wilson Bull. 109:470-480.

The authors investigated brown-headed cowbird habitat use of five forest edge types, and the forest interior of the 15,669-ha Green Ridge State Forest of Maryland in 1995. Cowbirds were detected in all habitats except the forest interior; occurring most frequently in forest-brush (50.0% of the points), -stream (46.3%), and -powerline (33.3%) edges. The results indicate that cowbirds in western Maryland select breeding areas based on distinct visible edges formed by canopy openings, occurrence of both high snag and vegetation volume at the forest edge, and the abundance of host species.

Keywords: habitat, Maryland

The author reports the highest recorded incidence of cowbird parasitism on marsh-nesting red-winged blackbirds.

Keywords: host species, brood parasitism

Ficken, M. S. 1967. Interactions of a crow and a fledgling cowbird. Auk 84:601-602.

The author documents the observation of a crow killing a begging brown-headed cowbird by dropping it and pecking it to death on June 5, 1965, at Medomak, Lincoln County, Maine.

Keywords: behavior, mortality, Maine

Finch, D. M. 1982. Rejection of cowbird eggs by crissal thrashers. Auk 99:719-724.

Although the brown-headed cowbird is sympatric with the crissal thrasher in the lower Colorado River valley, the author observed no parasitism in 15 thrasher nests. To determine whether or not the absence of cowbird eggs was caused by egg rejection, nine thrasher nests were experimentally parasitized. The cowbird eggs were ejected by thrashers in all the experimental nests. The author then compared thrasher nesting success to that of a sympatric acceptor, the Aberts towhee. Thrasher nesting success was significantly higher than nonparasitized or parasitized towhee nests. A higher predation rate accounted for the difference, but ejection of towhee eggs by cowbirds explained the great difference between nest success of parasitized towhees and thrashers. It is suggested that thrasher ejection behavior may either be a preadaptation or an evolved response to repeated cowbird parasitism.

Keywords: host defense, host species

Finch, D. M. 1983. Brood parasitism of the Aberts towhee: timing, frequency, and effects. Condor 85:355-359.

The effects of brood parasitism by the dwarf race of the brown-headed cowbird (M. a. obscurus) on the nesting success of the Aberts towhee in the lower Colorado River valley was studied from 1979 to 1980. The frequency of parasitism varied significantly over the breeding season. Since the mortality rates of young from nonparasitized towhee nests did not significantly change throughout the breeding season, the reduced success of towhee nests during the later portion of the breeding season is believed to be a result of cowbird parasitism. The relatively low success of cowbird eggs found in towhee nests suggests the towhees may not be favorable hosts.

Keywords: brood parasitism, host species

Fleischer, R. C. and N. G. Smith. 1992. Giant cowbird eggs in the nests of two icterid hosts: the use of morphology and electrophoretic variants to identify individuals and species. Condor 94:572-578.

The authors used electrophoresis of egg proteins and egg morphometric analyses to discriminate between the eggs of two host species and those of the giant cowbird, and to document the number of females that laid in a single host nest. Electromorph and color morph variations indicated that two or more female cowbirds laid eggs in six of ten nests containing two or more cowbird eggs. In the other four nests, paired cowbird eggs could not be differentiated and may have been laid by the same female.

Keywords: giant cowbird, egg mimicry

Fletcher, J. 1993. Is the shiny cowbird in Jamaica? Gosse Bird Club 61:5-7.

A first-person account of the first observation of shiny cowbirds in Jamaica on August 8, 1993.

Keywords: shiny cowbird, range expansion, Jamaica

Fleischer, R. C. 1985. A new technique to identify and assess the dispersion of eggs of individual brood parasites. Behav. Ecol. Sociobiol. 17:91-99.

A new technique for identifying eggs of brood parasites to individual females is presented. Dispersal patterns of eggs laid by brown-headed cowbirds over host species, time, and space were assessed. Despite small sample sizes, it is clear that individual cowbirds are not host-specific and overlap considerably in their laying areas.

Keywords: eggs

The author presents data on the frequency of brood parasitism on a study site near Lawrence, Kansas. The relationships among the frequency of parasitism, host nest density, host laying phenology, and nest or nest-site characteristics from 1981 to 1982 are assessed. The author also correlates geographic variation to percent parasitism and cowbird densities to determine whether the distribution of cowbird eggs over host nests fits that predicted by recent models using a Poisson expansion.

Keywords: brood parasitism, Kansas

Fleischer, R. C., A. P. Smyth, and S. I. Rothstein. 1987. Temporal and age-related variation in the laying rate of the parasitic brown-headed cowbird in the eastern Sierra Nevada, California. Can. J. Zool. 65:2724-2730.

Spatial, temporal, and age-related variation in the laying rate of female cowbirds in Mono County, California, was assessed by evaluating the ratio of live-trapped females containing an oviducal egg. A total of 75 examinations of 54 females of known age during 1984 revealed that the laying rates of yearling females were significantly lower than those of adults. The reduced laying rates of the yearling females are believed to be a result of a delay in the initiation of reproduction by yearlings, which may be due to a later arrival date on the breeding range.

Keywords: fecundity, California

Fleischer, R. C. and S. I. Rothstein. 1988. Known secondary contact and rapid gene flow among subspecies and dialects in the brown-headed cowbird. Evolution 42:1146-1158.

The authors analyzed the geographic variation of morphology for Sierra Nevadan cowbird populations based on the geographic structure of the populations by subspecies, and vocal dialects. Wing lengths of the longest-winged samples were significantly shorter than those of cowbirds collected in the same region between 1912 and 1922. Also, the wing lengths of Mammoth Lakes adult males and females during 1978-1981 are significantly larger than those of the 1982-1985 period. Vocal differences among these dialects do not appear to be a strong deterrent to gene flow.

Keywords: morphology, range expansion, vocalization

Fleischer, R. C., S. I. Rothstein, and L. S. Miller. 1991. Mitochondrial DNA variation indicates gene flow across a zone of known secondary contact between two subspecies of the brown-headed cowbird. Condor 93:185-189.

The authors present data on mitochondrial DNA (mt DNA) variation that are in accord with prior conclusions of extensive gene flow between subspecies M.a. obscurus and M.a. artemisiae.

Keywords: DNA, range expansion

Fletcher, L. B. 1925. A cowbirds maternal instinct. Bull. Northeastern Bird-Banding Assoc. 1:22-24.

On July 18th, 1924, in Cohasset, Massachusetts, the author observed a female cowbird feeding a fledgling cowbird on multiple occasions and speculates that cowbirds show more maternal behavior than previously believed.

Keywords: behavior, Massachusetts

Folkers, K. L. 1982. Host behavioral defenses to cowbird parasitism. Kansas Ornithol. Soc. Bull. 33:32-34.

The purpose of this study was to compare the defense against brown-headed cowbirds employed by certain acceptor and rejector species in Dickinson County, Iowa, in 1982. The author predicted that acceptors would behave more aggressively towards cowbirds than rejectors.

Keywords: host defense, host species, Iowa

Folkers, K. L. and P. E. Lowther. 1985. Responses of nesting red-winged blackbirds and yellow warblers to brown-headed cowbirds. J. Field Ornithol. 56:175-177.

The authors studied the aggressive responses of blackbirds and warblers to a model female cowbird. The hypothesis that hosts would be more aggressive early in the nesting cycle during the egg-laying stage was not clearly supported. The hypothesis does appear to apply more with nesting warblers and certain categories of blackbirds.

Keywords: host species, host defense.

Fox, A. C. 1940. Observations on the homing instinct of cowbirds (Molothrus ater). Bird-Banding 11:23.

This 1937 study documents the reoccurrence of two banded female cowbirds from a single location in North Dakota that returned to the same location for 2 subsequent years; and also returned to the banding site after being transported and released over 100 miles away.

Keywords: behavior, band recovery, North Dakota

Fraga, R. M. 1983. The eggs of the parasitic screaming cowbird (Molothrus rufoaxillaris) and its host, the bay-winged cowbird (M. badius): is there evidence for mimicry? J.Ornithol. 124:187-193.

The author attempted to follow the development of banded nestlings hatched from marked eggs in 1973. The author discovered some distinct differences between the nestlings of the host and parasite which allow for the correct identification of a larger number of eggs. This article focuses on the differences between the eggs of the screaming cowbird and bay-winged cowbird, however some comparisons with the eggs of other cowbirds are included.

Keywords: screaming cowbird, eggs

Fraga, R. M. 1984. Bay-winged cowbirds (Molothrus badius) remove ectoparasites from their brood parasites, the screaming cowbirds (M. rufoaxillaris). Biotropica 16:223-226.

The author describes the removal of ectoparasites and attributes this behavior to one of the factors selecting for the host specific behavior of screaming cowbirds, as ectoparasitism by flies and mites reach lethal levels at times.

Keywords: screaming cowbird

Fraga, R. M. 1985. Host-parasite interactions between chalk-browed mockingbirds and shiny cowbirds. Ornithol. Monog. 36:829-844.

The host-parasite interactions between a generalist brood parasite, the shiny cowbird, and one of its hosts, the chalk-browed mockingbird, were studied from 1972 to 1979 at a study site in Buenos Aires Province, Argentina. The mockingbird experienced a high parasitism rate of 78.1% (50 of 65 the mockingbird nests).

Keywords: shiny cowbird, host species, Argentina

Fraga, R. M. 1991. The social system of a communal breeder, the bay-winged cowbird Molothrus badius. Ethology 89:195-210.

The author describes observed cowbird behavioral, including collective agonistic displays, and suggests that this behavior may be indicative of group territoriality. This article describes the communal, cooperative breeding behavior of this cowbird.

Keywords: bay-winged cowbird, behavior

Fraga, R. M. 1996. Further evidence of parasitism of Chopi blackbirds (Gnorimopsar chopi) by the specialized screaming cowbird (Molothrus rufoaxillaris). Condor 98:866-867.

Data were obtained at Iguazu Airport, Misiones Province, Argentina, during 14 days between November 26, 1995 and January 14, 1996. The observation data indicate that screaming cowbirds have been using Chopi blackbirds as hosts in southeast Brazil and extreme northeast Argentina for more than 20 years.

Keywords: screaming cowbird, host species, Argentina, Brazil

Franzreb, K. E. 1987. Endangered status and strategies for conservation of the least Bells vireo in California. Western Birds 18:43-49.

The author gives a detailed summary of the life history of the vireo, and the factors leading to its decline, including cowbird parasitism. As a management plan, cowbird trapping is suggested.

Keywords: host species, population control, trapping, California

Frederick, P. C. and M. A. Shields. 1986. Corrections for the underestimation of brood parasitism frequency derived from daily nest inspections. J. Field Ornithol. 57:224-226.

The authors propose a model to estimate the frequency of intraspecific brood parasitism using nest monitoring. A potential shortcoming of this method is that the authors assume only one parasitic egg is laid in any clutch. If more than one is actually laid, this method gives a gross underestimation of the actual frequency of brood parasitism.

Keywords: intraspecific brood parasitism, model

Freeberg, T. M. 1996. Assortative mating in captive cowbirds is predicted by social experience. Anim. Behav. 52:1129-1142.

In 1993, the question of whether social experience affects pairing preferences for native cowbird populations was tested using a population from Indiana and another from South Dakota. During the first year of study, 71.4% of the pairings that occurred in a testing aviary were between unfamiliar birds of the same cultural background. In the second year of testing, following a winter of social experience with adults of their respective cultures, 86.2% of the pairings and 77.3% of the copulations that occurred were between birds of the same cultural background. These data demonstrate the learning of population-specific courtship and mating patterns in cowbirds, and are among the strongest experimental data to date indicating assortative mating in birds based upon social experience.

Keywords: behavior, mating system, Indiana, South Dakota

Freeman, S., D. F. Gori, and S. Rohwer. 1990. Red-winged blackbirds and brown-headed cowbirds: some aspects of a host-parasite relationship. Condor 92:336-340.

The overall rate of cowbird parasitism in red-winged blackbird nests in eastern Washington was 7.7%. The density of breeding blackbirds strongly affected parasitism rates among marshes within this study area, probably due to group nest defense. Over 20% of cowbird eggs laid in blackbird nests at this site appeared in inactive nests. The percentage of blackbird nests parasitized increased dramatically as the breeding season progressed.

Keywords: brood parasitism, host species, Washington

Friedmann, H. 1933. Further notes on the birds parasitized by the red-eyed cowbird. Condor 35:189-191.

The author adds 22 species to the previous list of 10 host species of the bronzed cowbird, chiefly based on unpublished material obtained from private collections.

Keywords: host species, bronzed cowbird

Friedmann, H. 1934. Additional notes on the birds victimized by the shiny cowbird (Molothrus bonariensis). Ibis 4:340-347.

To the 123 species and subspecies of birds previously listed as hosts of the shiny cowbird, the author adds 14 others, bringing the total to 137 known host species.

Keywords: host species, shiny cowbird

Friedmann, H. 1929. The cowbirds: a study in the biology of social parasitism. Charles C. Thomas. Springfield, Illinois.

Keywords: brood parasitism

Friedmann, H. 1931. Additions to the list of birds known to be parasitized by the cowbirds. Auk 48:52-65.

The author adds several new hosts to the list of species parasitized by cowbirds.

Keywords: host species

Friedmann, H. 1934. Further additions to the list of birds victimized by the cowbird. Wilson Bull. 46:25-36.

The author adds a few more species of cowbird hosts to lists from his earlier publications. Keywords: host species

Friedmann, H. 1938. Additional hosts of the parasitic cowbirds.

Auk 55:41-50.

Since the authors last publication, considerable additional information on host species of cowbirds has been gathered.

Keywords: host species

Friedmann, H. 1943. Further additions to the list of birds known to be parasitized by the cowbirds. Auk 60:350-356.

In the past 4 years, several additional host records of the various cowbirds have been added to previous compilations.

Keywords: host species

Friedmann, H. 1949. Additional data on victims of parasitic cowbirds. Auk 66:154-163.

The author presents additions to previous publications of new host species, and new data on already determined host species.

Keywords: host species

Friedmann, H. 1963. Host relations of the parasitic cowbirds. U.S. Natl. Mus. Bull. 233.

For the two North American species (brown-headed and bronzed cowbirds), the author submits complete annotated catalogs of their hosts. He has included a complete tabular outline of the known hosts of each of the races of the cowbirds.

Keywords: host species

Friedmann, H. 1964. The history of our knowledge of avian brood parasitism. Centaurus 10:282-304.

The five families of birds containing brood parasites are discussed: cuckoos, cowbirds, honey-guides, weaverbirds, and ducks.

Keywords: brood parasitism

Friedmann, H. 1966. Additional data on the host relations of the parasitic cowbirds. Smithsonian Miscellaneous Collection 149.

The author has added a few recently published records of the cowbird to his 1963 book.

Keywords: host species

Friedmann, H. 1971. Further information on the host relations of the parasitic cowbirds. Auk 88:239-255.

The author brings together a number of recent records involving additional host species of cowbirds, including some that amplify earlier data on previously known hosts. Some records have been gathered from the widely scattered literature presented in the past few years; others are unpublished records provided to the author by their reporters.

Keywords: host species

Friedmann, H., L. F. Kiff, and S. I. Rothstein. 1977. A further contribution to knowledge of the host relations of the parasitic cowbirds. Smithsonian Contributions to Zoology 235.

Authors summarize a list of host species with information regarding frequency of parasitism and host defense adaptations.

Keywords: host species, host defense

Friedmann, H. and L. F. Kiff. 1985. The parasitic cowbirds and their hosts. Proc. West. Found. Vertebr. Zool. 2:226-302.

A summary of current knowledge of the various species of cowbirds and their hosts is presented. Accordingly, this paper is limited to the three generalist parasites. Paper is prefaced with a discussion of the basic biological problem of reproductive fecundity.

Keywords: brood parasitism, host species

Fulton, J. T. 1990. The shiny cowbird (Molothrus bonariensis) reaches Alabama. Alabama Birdlife 37:1-3.

A first-person account of the first sighting of this cowbird in Alabama on April 25, 1990.

Keywords: shiny cowbird, range expansion, Alabama

Gates, J. E. and N. R. Giffen. 1991. Neotropical migrant birds and edge effects at a forest-stream ecotone. Wilson Bull. 103:204-217.

Species richness, density, and avian diversity were assessed across a deciduous-coniferous forest gradient between a ridge crest and stream bottom. The 1981 study was conducted in Garrett County, Maryland, a region in the central Appalachian Mountains that is 71.2% forested. Data suggest conditions at certain forest-stream edges might be conducive to increased nest predation and cowbird parasitism within forested landscapes that are minimally fragmented by human activities.

Keywords: brood parasitism, habitat, Maryland

Gates, J. E. and D. R. Evans. 1998. Cowbirds breeding in the central Appalachians: spatial and temporal patterns and habitat selection. Ecol. Appl. 8:27-40.

To assess the impact of cowbird brood parasitism on Nearctic-Neotropical migrants, spatial and temporal patterns and habitat selection of female cowbirds throughout the breeding season were determined. Using radiotelemetry, cowbird movements were monitored in 3-hour time periods over the course of the day, beginning at 0500 hours. The results suggest that management efforts designed to reduce cowbird use of forested tracts in this region would include eliminating feeding areas, minimizing canopy openings or edges, and perhaps managing existing edges in order to disperse potential host species nests.

Keywords: habitat, movements, radio telemetry

Gibbs, H. L., P. Miller, G. Alderson, and S. G. Sealy. 1997. Genetic analysis of brown-headed cowbirds Molothrus ater raised by different hosts: data from mtDNA and microsatellite DNA markers. Molecular Ecology 6:189-193.

Study tested the hypothesis that there should be no genetically differentiated host races within cowbird populations. Differentiation in two rapidly evolving DNA markers (mtDNA control region sequence and nuclear DNA microsatellite loci) among unrelated cowbird

chicks raised by two ecologically distinct hosts were compared. Study results revealed no differentiation in either marker, supporting the absence of host race hypothesis.

Keywords: DNA

Gill, S. A. and S. G. Sealy. 1996. Nest defense by yellow warblers: recognition of a brood parasite and an avian nest predator. Behaviour 133:263-282.

Yellow warblers were subjected to taxidermic mounts of a brood parasite (brown-headed cowbird), avian nest predator (grackle), and control (sparrow) during their egg laying and nestling stages in an effort to determine whether warblers were able to distinguish between the threats of brood parasitism and predation. Warblers responded more intensely to the cowbird at the egg laying stage, performing two unique behaviors (seet calling and nest-protection behavior). In contrast, the greatest warbler response to the grackle occurred during the nestling stage, consisting largely of alarm calls. The sparrow model infrequently elicited aggressive behavior during the egg laying and nestling stage. The responses support the hypothesis that warblers discriminate between threats of brood parasitism and nest predation.

Keywords: brood parasitism, host defense

Gill, S. A., D. L. Neudorf, and S. G. Sealy. 1997. Host responses to cowbirds near the nest: cues for recognition. Anim. Behav. 53:1287-1293.

Two cues (bill shape and vocalizations) that yellow warblers may use to recognize brown-headed cowbirds were examined experimentally. Female warblers responded more intensely to a control cowbird than one with a longer, thinner bill, suggesting that bill shape was an important cue in recognition. Female warblers were also able to distinguish between male and female cowbird vocalizations and those of a song sparrow. Results suggest that female yellow warblers recognize cowbirds on the basis of bill shape and vocalizations, but are unable to distinguish between male and female cowbirds based on appearance.

Keywords: host defense, host species

Gill, S. A., P. M. Grieef, L. M. Staib, and S. G. Sealy. 1997. Does nest defense deter or facilitate cowbird parasitism? A test of the nesting-cue hypothesis. Ethology 103:56-71.

The authors tested the hypothesis that cowbirds may use nest-defense responses directed toward them by hosts as cues to locate nests to parasitize. A female cowbird model was placed at three distances from the host nests and the responses elicited were compared between species. All species responded to the cowbird at all distances. The hosts of parasitized nests did not respond more intensely than those of unparasitized nests to the cowbird positioned at any of the distances from the nest. Results do not support the nesting-cue hypothesis and suggest that nest defense is not likely to be used as a nest-location cue.

Keywords: host defense

Gillespie, J. 1930. Homing instinct in cowbirds. Bird-Banding 1:42.

A first-person account of a female cowbird returning to a trap site in Glenolden, Pennsylvania, after repeatedly being relocated up to 20 miles away.

Keywords: behavior, movement, trapping

Glegg, W. E. 1950. Gradation of variation of eggs of the Argentine cowbird. Bull. Brit. Ornithol. Club 70:4-5.

The author describes a collection of shiny cowbird eggs taken from nests at two different locations that varied from immaculate white to heavily mottled.

Keywords: shiny cowbird, eggs

Gochfeld, M. 1978. Begging by nestling shiny cowbirds: adaptive or maladaptive. Living Bird 17:41-48.

The author considers that the begging behavior of cowbird nestlings may be a special adaptation that improves the survival of the cowbird chick.

Keywords: shiny cowbird, behavior

Gochfeld, M. 1979. Brood parasite and host coevolution: interactions between shiny cowbirds and two species of meadowlarks. Amer. Nat. 113:855-870.

This study was conducted to attempt to determine how the shiny cowbird preferentially selects among two potential host species, and what cowbird nest-finding behavior and possible anti-parasite host strategies have emerged. The author concludes that the apparent ability of the cowbird to distinguish between two similar meadowlark species reflects the higher suitability of one of these species.

Keywords: brood parasitism, shiny cowbird

Goddard, S. V. 1969. Fall and winter food habits of red-winged blackbirds and brown-headed cowbirds in western Oklahoma. Wilson Bull. 81:336-337.

The author gives a detailed summary of the stomach contents of blackbirds and cowbirds from Custer County, Oklahoma, in 1964 and 1965. Grain sorghum and ragweed were the two most commonly consumed seeds.

Keywords: diet, Oklahoma

Goertz, J. W. 1977. Additional records of brown-headed cowbird nest parasitism in Louisiana. Auk 94:386-389.

During 13 consecutive nesting season surveys (1963 to 1975), 7,360 active (with eggs or young) nests of 111 species of birds were examined one or more times. No parasitism was observed among 1,824 active nests of 61 nonpasserine species representing 27 families and 14 orders. Parasitism occurred only 17 times in the remaining 5,536 active passerine nests, an incidence of 1.3%.

Keywords: host species, brood parasitism

Goguen, C. B. and N. E. Matthews. 1996. Nest desertion by blue-gray gnatcatchers in association with brown-headed cowbird parasitism. Anim. Behav. 52:613-619.

The nesting success of a gnatcatcher population, which often deserts nests when parasitized by cowbirds, was studied to examine the success of the desertion response and to determine factors that stimulate desertion. Of 83 gnatcatcher nests, 76% were parasitized; 45% of the nests parasitized during the egg-laying stage were deserted. Desertion occurred independently of the timing of the parasitism event during the breeding season and the number of cowbird eggs laid per nest. Nest desertion by gnatcatchers appears to be a generalized response to a disturbance at the nest induced by cowbirds. The cue that elicits the desertion response remains unclear.

Keywords: host defense, host species

Goguen, C. B. and N. E. Matthews. 1998. Songbird community composition and nesting success in grazed and ungrazed pinyon-juniper woodlands. J. Wildl. Manage. 62:474-484.

Habitat structure, songbird abundance, and nesting productivity were compared between actively grazed and long-term ungrazed areas within the pinyon-juniper woodlands of northeastern New Mexico. From 1992 to 1995, authors performed vegetation sampling, conducted songbird point counts, and located and monitored nests on eight 35-ha study plots. Four plots experienced moderate cattle grazing and four were ungrazed since 1973. No differences in brown-headed cowbird parasitism rates for the major hosts between grazed and ungrazed areas were detected. Greater than 75% of the nests of three species were parasitized on both treatments.

Keywords: brood parasitism, habitat, host species, New Mexico

Goist, K. C., J. N. Bull, E. S. Chaffee, M. E. Gaasch, K. C. Goist, Jr., S. Lumpkin, J. W. McDaniel. 1976. Control of cowbird parasitism on the Kirtlands warbler through use of natural behavior patterns. Unpublished manuscript available at Psychology Dept., Adrian College, Adrian, Michigan.

Keywords: behavior

Graham, D. S. 1988. Responses of five host species to cowbird parasitism. Condor 90:588-591.

Nest records, compiled at the Ontario Nest Record Scheme, were reviewed to assess the response of cowbird parasitism on red-eyed vireos, yellow warblers, northern cardinals, chipping sparrows, and song sparrows. Nest desertion was the principal response for rejecting cowbird eggs. In addition to nest desertion, yellow warblers rejected cowbird eggs by burying clutches under a second nest bottom. The probability of rejection did not vary during the breeding season or between multiple- and single-parasitized pairs. Possible stimuli used by hosts to recognize parasitism are discussed in this report.

Keywords: host species, host behavior, host defense

Graham, D. S. 1989. Rejection, desertion, burial, and the wanton layers. Living Bird:20-24.

This report provides a detailed overview of brood parasitism and host defenses, and lends some insight into the evolutionary origin of this type of reproduction.

Keywords: brood parasitism, evolution, host defense

Graham, D. S. and A. L. A. Middleton. 1989. Conspecific recognition by juvenile brown-headed cowbirds. Bird Behaviour 8:14-22.

In an attempt to better understand the sensory mode initially used by juvenile cowbirds to recognize conspecifics, nestling cowbirds were removed from host nests and raised in varying degrees of isolation. Juvenile cowbirds, 25 and 35 days old, were placed in a test arena and exposed to mounted blackbird specimens. Cowbirds which were 25 days old did not show preference for mounted cowbird specimens, however in some instances, the 35-day- old juveniles did. In another test, neither 22- nor 32-day-old cowbirds associated preferentially with a speaker emitting a cowbird vocalization. These findings suggest that juvenile cowbirds initially use visual cues to recognize conspecifics at the time they become independent of their hosts, and may develop recognition with age and experience.

Keywords: behavior

Griffith, J. T. and J. C. Griffith. 1993. Brown-headed cowbird trapping and least Bells vireo recovery on Marine Corps Base Camp Pendleton, 1983-1993.

Abstract of the North American Research Workshop on the Ecology and Management of Cowbirds. The Nature Conservancy of Texas, Austin.

Keywords: trapping, Texas

Grinnell, J. 1909. A new cowbird of the genus Molothrus, with a note on the probable genetic relationships of the North American forms. University of Calif. Publ. Zool. 5:275-281.

This study investigates whether the cowbirds of the Great Basin are subspecifically distinct from those of the Eastern United States and suggests they are more closely related to the subspecies which inhabit the region from Arizona and southeastern California southward through Mexico.

Keywords: subspecific variation, Great Basin

Grinnell, J. 1934. The race of cowbird in the San Francisco Bay region. Condor 36:218-219.

Recently obtained specimens from the San Francisco Bay area in 1934 were given the subspecies name of dwarf cowbird (M. a. obscurus). This subspecies inhabits the western and southern regions of California.

Keywords: subspecies, California

Grzybowski, J. A. 1995. Carolina wrens fledge brown-headed cowbird chick. Bull. Oklahoma Ornithol. Soc. 28:6-7.

This report documents Carolina wrens fledging a cowbird chick in Cleveland County, Oklahoma, in 1993.

Keywords: host species, nest parasitism, Oklahoma

Grzybowski, J. A. and V. W. Fazio III. 1991. Shiny cowbird reaches Oklahoma. American Birds 45:50-52.

This article describes the first record of a shiny cowbird being collected in Oklahoma on June 12, 1990.

Keywords: range expansion, shiny cowbird, Oklahoma

Gustad, J. R. 1995. The Norwegian brown-headed cowbird. Brit. Birds 88:377.

This article is a letter correcting McKay (1994) regarding the condition of a female cowbird found in Norway.

Keywords: range expansion, Norway

Gustafson, E. J., T. R. Crow, and F. R. Thompson. 1993. Assessing the impact of forest management strategies on the vulnerability of forest birds to cowbird brood parasitism with a spatially explicit GIS model. Bull. Ecol. Soc. Amer. 74:260.

A GIS model was developed to predict the spatial distribution of cowbird parasitism rates from a land cover map. Abstract only.

Keywords: brood parasitism, GIS, habitat, model

Gustafson, E. J. and T. R. Crow. 1994. Modeling the effects of forest harvesting on landscape structure and the spatial distribution of cowbird brood parasitism. Landscape Ecology 9:237-248.

A timber harvest allocation model used to identify areas for clear cutting while maintaining the appearance and values of a managed landscape was evaluated using a GIS model. The effectiveness of the timber harvest model was tested by using a generalized neotropical migrant forest bird and utilizing a GIS model that generated a map layer showing the spatial distribution of the relative vulnerability of forest birds to brood parasitism by brown-headed cowbirds. The application of the cowbird model to landscapes managed under different strategies could help managers decide where harvest activity would produce the least negative impact on breeding forest birds.

Keywords: brood parasitism, GIS, habitat, model

Haas, C. A. and K. H. Haas. 1998. Brood parasitism by brown-headed cowbirds on brown thrashers: frequency and rates of rejection. Condor 100:535-540.

Report documents that the average observed rate of brood parasitism on nests of brown thrashers was higher than typically reported from 1984-1986. An experiment to determine if these high observed rates of parasitism were a result of unusually high rates of parasitism by cowbirds or unusually low rates of rejection by thrashers was conducted. Results showed that brown thrashers removed 58% of experimentally placed cowbird eggs, indicating thrashers in this area are parasitized at a high rate, but that low rates of rejection are at least partially responsible for the high rate of parasitism. These results further suggest that the classification of brown thrashers as a rejector species should be reevaluated.

Keywords: brood parasitism, egg manipulation, eggs

Hahn, D. C. and R. C. Fleischer. 1995. DNA fingerprint similarity between female and juvenile brown-headed cowbirds trapped together. Anim. Behav. 49:1577-1580.

DNA fingerprinting study investigates whether female brown-headed cowbirds associate with their own juvenile offspring at feeding sites more often than would be expected by chance. Thirty-six adult female-juvenile pairs (or trios) of cowbirds were trapped and DNA fingerprinting analyses were conducted to calculate similarity indices and to compare S-values. The results suggest that adult cowbirds associate with juveniles, in some cases their own offspring, and that this association may play an important role in the behavioral development of the juveniles.

Keywords: behavior, DNA

Hahn, D. C. and J. S. Hatfield. 1995. Parasitism at the landscape scale: cowbirds prefer forests. Conserv. Biol. 9:1415-1424.

In a 2-year study (1991-1992) in Dutchess County, New York, parasitism rates on a particular host species were significantly higher within the forest-interior community than on an adjacent old field and edge community. Cowbirds parasitized a mature 1300-ha forest stand even though their traditional host species were available in adjacent old-field and edge habitats. From a management perspective, these data suggest that cowbirds exhibit regional differences in host and habitat use, the target host community of a particular cowbird population is unpredictable at the landscape scale, and a landscape scale should be used in designing cowbird studies to accurately assess local population dynamics and potential impacts resulting from brood parasitism.

Keywords: habitat, brood parasitism, New York

Hamas, M. J. 1980. Eastern kingbird rejection of brown-headed cowbird eggs. Jack-Pine Warbler 58:33.

This report summarizes an experiment of artificially parasitizing one kingbird nest three times near Mt. Pleasant, Michigan, in 1977. All three eggs were ejected.

Keywords: host behavior, host defense, egg manipulation, Michigan

Hamerstrom, F. 1947. House wren feeding a cowbird. Wilson Bull. 59:114.

Report is a first-person account of a wren feeding a cowbird in southeastern Michigan in 1946.

Keywords: host species

Hamilton, W. J. III. 1957. Blue-winged teal nest parasitized by brown-headed cowbird. Wilson Bull. 69:279.

A 1956 report from Manitoba, Canada, documents the parasitism of a blue-winged teal by a brown-headed cowbird, where the host incubates only two cowbird eggs and none of its own.

Keywords: host species

Hamilton, W. J. III, and G. H. Orians. 1965. Evolution of brood parasitism in altricial birds. Condor 67:361-382.

The evolution of brood parasitism is investigated by studying the behavioral patterns and environmental circumstances which may have contributed to this adaptation. In an attempt to better understand the evolution of brood parasitism, parasitic adaptations are compared to those of nonparasitic relatives of modern brood parasites. Why individual species developed parasitic traits, while others did not, is also discussed.

Keywords: behavior, brood parasitism, evolution

Hamilton, K. S., A. P. King, D. R. Sengelaub, and M. J. West. 1997. A brain of her own: a neural correlate of song assessment in a female songbird. Neurobiology of Learning and Memory 68:325-332.

The authors studied brown-headed cowbirds, a species in which only males sing but in which females discriminate between males on the basis of song. The study focused on nucleus IMAN, since it is believed to play a role in the early development of song acquisition.

Keywords: vocalization

Hanka, L. R. 1979. Choice of host nest by the brown-headed cowbird in Colorado and Wyoming. Condor 81:436-437.

In 1977 and 1978, brood parasitism patterns were documented from the plains, foothills, mountain river valleys, and mountain parks of north-central Colorado and south-central Wyoming.

Keywords: host species, habitat, Colorado, Wyoming

Hanka, L. R. 1984. A brown-headed cowbird parasitizes northern orioles. Western Birds 15:33-34.

A first-person report of observing cowbird eggs in two oriole nests near Fort Collins, Colorado, in 1977. The cowbird eggs were tested for permeability to water vapor, an expression of the genom of a female. The eggs had identical permeabilities to water vapor and were assumed to be laid by the same female.

Keywords: eggs, host species, Colorado

Hanka, L. R. 1985. Recent altitudinal range expansion by the brown-headed cowbird in Colorado. Western Birds 16:183-184.

In 1977 and 1978, while conducting a study of cowbird parasitism in Colorado, the author noted substantial differences in the cowbirds range from that described in earlier literature. Cowbirds were found to be as common in the mountain parks and river valleys as in the foothills. Cowbirds were observed as high as 2895 m, however the highest parasitized nests were found at an elevation of 2475 m.

Keywords: range expansion, Colorado

Hann, H. W. 1941. The cowbird at the nest. Wilson Bull. 53:211-221.

The author gives a brief review of literature on the finding and observation of nests by cowbirds, egg laying, and the acceptance of eggs by the host. The case study involved the documentation of cowbird behavior while parasitizing an ovenbird nest near Ann Arbor, Michigan.

Keywords: behavior, brood parasitism, Michigan

Hanna, W. C. 1928. Notes on the dwarf cowbird in California. Condor 30:161.

The author reports an increase in known cowbird host from 4 species to 12 species.

Keywords: host species, California

Hanna, W. C. 1933. House finch parasitized by dwarf cowbird and black phoebe nests occupied by house finch. Condor 35:205.

This report documents the parasitism of a house finch, a rare host. The nest contained three eggs of the finch and one of the cowbird. This article also presents information on three black phoebe nests, two of which contained eggs of the house finch.

Keywords: host species

Hanna, W. C. 1934. The black-tailed gnatcatcher and the dwarf cowbird. Condor 36:89.

A first-person account of cowbird parasitism of this species.

Keywords: host species

Hanna, W. C. 1936. Vermillion flycatcher a victim of the dwarf cowbird in California. Condor 38:174.

A first-person record of the first two occurrences of cowbird parasitism in the State of California, Riverside County, 1935.

Keywords: host species

Harmon, W. H. 1928. Notes on the dwarf cowbird in southern California. Condor 30:161.

The author changes the previous estimate of 4 local host species to 12.

Keywords: host species, California

Harris, J. H. 1991. Effects of brood parasitism by brown-headed cowbirds on willow flycatcher nesting success along the Kern River, California. Western Birds 22:13-26. This study compares the willow flycatchers nesting microhabitat and nest characteristics of lowland riparian forests and montane meadows. Brood parasitism by the brown-headed cowbird was the leading cause of nest failure; at least 68% of flycatcher nests were parasitized. The most common response of flycatchers to parasitism was nest abandonment followed by renesting attempts. This strategy proved to be successful, however fledging dates were often delayed 2 to 4 weeks. This study also supports the hypothesis that the rates of brood parasitism are indirectly related to elevation.

Keywords: host species, brood parasitism

Harrison, H. H. 1952. Notes on a cowbird removing an egg at dawn. Redstart 19:46-49.

The author photographs a female cowbird removing a chestnut-sided warbler egg at dawn from its nest on May 25, 1946, near Cooperstown in Butler County, Pennsylvania.

Keywords: host species, Pennsylvania

Harrison, H. H. 1973. The cowbird strikes at dawn. National Wildlife. 11:33-37.

A series of photographs documenting the removal of host eggs by female cowbirds at dawn, and adult and young cowbirds at host nests.

Keywords: brood parasitism

Hatch, S. A. 1983. Nestling growth relationships of brown-headed cowbirds and dickcissels. Wilson Bull. 95:669-671.

The author presents an analysis of data collected in 1974 on the growth relationships of cowbirds and dickcissels in prairie habitat in eastern Kansas (Konza Prairie Research Natural Area) where cowbird parasitism rates were extremely high. Data suggest that the growth of cowbird chicks and their hosts may be influenced to a considerable degree by behavioral interactions.

Keywords: host species, behavior, Kansas

Hedge, R. L. 1996. Magnolia warbler observed feeding brown-headed cowbird fledgling: Indianas first breeding record. Indianas Audubon Quarterly 74:135-137.

A summary of Indianas first record of breeding warblers in 1994 and 1995.

Keywords: host species, Indiana

Henninger, W. F. 1902. A new foster-parent of the cowbird. Auk 19:400-401.

In 1902, at Ross County, Ohio, the author discovered a Bewicks wren nest that contained a cowbird egg. This species was previously unrecorded as a cowbird host.

Keywords: host species, Ohio

Hergenrader, G. L. 1962. The incidence of nest parasitism by the brown-headed cowbird (Molothrus ater) on roadside nesting birds in Nebraska. Auk 79:85-88.

A total of 560 km (338 miles) of Nebraska roadsides was searched for bird nests during the summer of 1960 in an effort to determine the incidence of nest parasitism by cowbirds on host species that commonly nest along roadsides. Fifty-four percent of the 59 red-winged blackbird nests was parasitized. Of the 17 dickcissel nests located, 53% was parasitized as was 16% of the 31 meadowlark nests. No parasitized nests of either the brown thrasher or mourning dove were found.

Keywords: brood parasitism, host species, Nebraska

Hernandez, M. D. 1986. Brown-headed cowbirds feeding young in Coffee County, Tennessee. Migrant 57:98.

A 1985 account of a male and female cowbird feeding a young cowbird also being cared for by the host.

Keywords: behavior, Tennessee

Hicks, L. E. 1934. A summary of cowbird host species in Ohio. Auk 51:385-386.

Since 1918, the author maintained a nearly complete record of all bird nests located and brief notes on those containing cowbird eggs or young. During periods over eight summers in Ohio, nearly 5,000 nest were located in Ashtabula County, 2,740 others were found in

Franklin County, 2,435 in Knox County, and about 3,320 elsewhere in the state. A total of 42 species served as hosts and are listed in this article.

Keywords: host species, Ohio

Hienz, R. D., J. M. Sinnott, and M. B. Sachs. 1977. Auditory sensitivity of the red-wing blackbird (Agelaius phoeniceus) and the brown-headed cowbird (Molothrus ater). J. Comp. Physiol.  Psychol. 91:1365-1376.

Auditory sensitivity of blackbirds and cowbirds was measured with a series of keys that emitted varying levels of tones when pressed. All procedures produced similar thresholds for both blackbirds and cowbirds; hearing encompassed the range from 125 Hz to 10 kHz, with lowest thresholds of 4 to 20 dB in the 2- to 4-kHz range.

Keywords: hearing

Higgins, K. F. 1971. Cowbird parasitism of an upland plover nest. Prairie Nat. 3:79.

A first-person account documenting the second case of cowbird parasitism of an upland plover nest, in 1971, Stutsman County, North Dakota.

Keywords: host species

Hill, D. P. and S. G. Sealy. 1994. Desertion of nests parasitized by cowbirds: have clay-coloured sparrows evolved an anti-parasite strategy? Anim. Behav. 48:1063-1070.

Clay-coloured sparrow nests were experimentally parasitized and manipulated to assess whether desertion is an anti-parasite defense. Nest desertion occurred only when associated with clutch reduction, i.e., egg removal. Therefore, desertion is a result of egg removal, more so than actual parasitism.

Keywords: host defense, host species, Manitoba, Canada

Hill, R. A. 1976. Host-parasite relationships of the brown-headed cowbird in a prairie habitat of west-central Kansas. Wilson Bull. 88:555-565.

This report documents the extent of cowbird parasitism and discusses host adaptations to parasitism in a predominantly prairie habitat. The study was conducted in west-central Kansas in 1973 and 1974. Data from all available Ellis County nesting records were used to determine the frequency of parasitism for each host species. The frequency of parasitism varied from 2.7% (Says phoebe) to 100% (cardinal). All but one grassland host species received moderate to heavy parasitism. Defense of cowbird parasitism by horned larks involved nesting prior to the cowbirds breeding season. Lark buntings either deserted their nests or ejected the cowbird eggs as their defense.

Keywords: brood parasitism, host species, habitat, Kansas

Hobson, K. A. and S. G. Sealy. 1989. Responses of yellow warblers to the threat of cowbird parasitism. Anim. Behav. 38:510-519.

Responses of yellow warblers to a model female cowbird and a fox sparrow control were tested during the nest-building, egg-laying, incubation, and nestling stages. Female warblers rarely responded aggressively to the models or showed distraction displays. However, a nest-protection behavior involving seet calling and a rush to sit in the nest was observed, primarily in response to the cowbird model. The frequency of seet calling by females was highest during egg laying when they were most susceptible to cowbird parasitism. Male warblers responded infrequently to all models and were the first to arrive in only 5% of trials.

Keywords: host species, host defense, behavior

Hodges, M. and J. Toups. 1979. Bronzed cowbird - first Mississippi records. Mississippi Kite 9:2-4.

On January 6, 1979, the authors observed the first recorded bronzed cowbirds in the state of Mississippi.

Keywords: bronzed cowbird, range expansion, Mississippi

Hoffman, E. C. 1929. Cowbirds decoys incubation period. Bull. Northeastern Bird-Banding Assoc. 5:118-119.

This article presents brief notes over the 12-day incubation period of a cowbird egg, and the observation of a cowbird nestling ejecting a song sparrow nestling in 1928.

Keywords: host species, incubation

Hoffman, W. and G. E. Woolfenden. 1986. A fledgling brown-headed cowbird specimen from Pinellas County. Florida Field Naturalist 14:18-20.

This report documents the first evidence of breeding cowbirds in Pinellas County, Florida, and discusses recent increases in cowbird populations in the Tampa Bay area.

Keywords: range expansion, Florida

Hofslund, P. B. 1957. Cowbird parasitism of the northern yellow-throat. Auk 74:42-48.

During the summers of 1948 through 1951, the author conducted an intensive study into the life history of the northern yellow-throat. The summers of 1948 and 1949 were spent observing a population near Ann Arbor, Michigan, and the summers of 1950 and 1951 were spent observing populations near Duluth, Minnesota. The relationship between yellow-throats and cowbirds was a focal point of the study. Study results indicate that the cowbird is moderately successful when parasitizing the yellowthroat. Cowbird parasitism serves as a control on the yellow-throat population, primarily during the egg-laying and incubation period. A reduction in host success occurs through the deliberate removal or accidental puncture of eggs leading to nest desertion, and the heat generated during incubation being absorbed to a greater extent by the cowbird eggs.

Keywords: host species, brood parasitism, Michigan, Minnesota

Hofstead, R. 1950. Cowbird-wood thrush relationship. Flicker 22:108-109.

A first-person account of cowbird parasitism of wood thrush nests near St. Paul, Minnesota. One nest contained two damaged thrush eggs and nine cowbird eggs, another was observed with an incubating thrush on four cowbird eggs and, when the nest was destroyed, renested and again was seen incubating four cowbird eggs.

Keywords: brood parasitism, host species, Minnesota

Hohn, E. O. 1959. Prolactin in the cowbirds pituitary in relation to avian brood parasitism. Nature 184:2030.

The author compares the prolactin content of the pituitaries of female cowbirds in breeding condition with that of pituitaries of breeding females of the closely related red-winged blackbird. The results suggest that failure to respond to prolactin rather than lack of prolactin production is involved in the failure of female cowbirds to form brood patches.

Keywords: endocrinology

Holcomb, L. C. 1968. Reaction of mourning doves to cowbird eggs. Wilson Bull. 80:105.

The author experimentally placed cowbird and red-winged blackbird eggs in the nests of mourning doves in 1966 near Fremont, Nebraska, to determine why doves experience a reduced level of parasitism. Results indicate that mourning doves are tolerant to other eggs in their nests, however eggs laid on the frail nest platform of the mourning dove are likely to be accidentally knocked off.

Keywords: host species, egg manipulation, Nebraska

Holford, K. C. and D. R. Roby. 1993. Factors limiting fecundity of captive brown-headed cowbirds. Condor 95:536-545.

Experiments with captive cowbirds were conducted to determine potential limiting factors for egg production. The fecundity of females deprived of host nests was not significantly different from that of the controls. Results suggest that fecundity of cowbirds may be limited by dietary calcium, but not by the availability of host nests. The fecundity of individual females averaged 26.3 eggs, significantly greater than that of the same females as yearlings. The authors suggest that cowbirds appear to be under intense selection pressure to produce eggs at a high rate, however the ability of wild females to acquire sufficient dietary calcium to form egg shells may limit fecundity.

Keywords: fecundity, laying rate, eggs

Holmgren, M. A. and P. W. Collins. 1995. Interim report on the distribution, breeding status, and habitat associations of seven federal special-status bird species and brown-headed cowbirds at Vandenberg Air Force Base, Santa Barbara County, California. Mus. Sys. Ecol., Dept. of Ecol., Evolution, and Marine Biol., University of California: Santa Barbara, California. Environmental Report No. 3.

Keywords: habitat, host species, California

Honecker, J. F. 1902. A cowbirds nest. Amer. Ornithol. 2:164.

A first-person observation of a pair of cowbirds building a nest and fledging four young while being held captive in 1899.

Keywords: behavior

Hoover, J. P. and M. C. Brittingham. 1993. Regional variation in cowbird parasitism of wood thrushes. Wilson Bull. 105:228-238.

Researchers analyzed thrush nest records from the Cornell Laboratory of Ornithology Nest Record Program to evaluate whether rates of cowbird parasitism of the thrush varied regionally and whether parasitism rates were correlated with differences in abundance of cowbirds or thrushes. Changes in regional parasitism rates from 1960-1989 were also evaluated. Parasitism rates were correlated positively with relative abundance of cowbirds and negatively correlated with the relative abundance of the wood thrush.

Keywords: brood parasitism, host species

Hostetler, P. H. 1994. A comparison of brown-headed cowbird abundance between forest edges and interior. Missouri Acad. Sci. 28:128.

This study was conducted to determine cowbird relative abundance at edges in three forest sites located in the south-central Ozark region of Missouri in 1993. Abstract only.

Keywords: abundance, habitat, Missouri

Hoy, G. and J. Ottow. 1964. Biological and oological studies of the Molothrine cowbirds (Icteridae) of Argentina. Auk 81:186-203.

Observations over an 8-year period in the provinces of Salta and Jujuy, northwestern Argentina, provide additional information on three species of Molothrus (M. bonariensis, rufo-axillaris, and badius) that supplements data published by Friedmann (1929). Data on field observations and egg collection are discussed.

Keywords: life history, Argentina

Hudson, W. H. 1874. On the procreant instincts of the three species of Molothrus found in Buenos Ayres. Proc. Zool. Soc. London 11:153-174.

A collection of notes on the parasitic behavior of several Molothrine species.

Keywords: behavior, Argentina

Hunter, J. E. 1994. Further observations of head-down displays by brown-headed cowbirds. Western Birds 25:63-65.

This article is a first-person account of observations involving a cowbird performing the head-down display directed toward a female rusty blackbird in Humboldt County, California, in 1992.

Keywords: behavior, California

Hutcheson, W. H. 1990. Shiny cowbird collected in South Carolina: first North American specimen. Wilson Bull. 102:561.

A summary on the collection of the first specimen of the shiny cowbird in North America on Sullivans Island, South Carolina in 1989.

Keywords: shiny cowbird, range expansion, South Carolina

Igl, L. D. and D. H. Johnson. 1997. Changes in breeding bird populations in North Dakota: 1967 to 1992-93. Auk 114:74-92.

The authors compared breeding bird populations in North Dakota using surveys conducted in 1967 and 1992-1993. In decreasing order, the five most frequently occurring species were horned lark, brown-headed cowbird, western meadowlark, red-winged blackbird, and eastern kingbird. Although species composition remained relatively similar throughout the years of study, between-year patterns in abundance and frequency varied considerably among species. Data from this survey and the North American Breeding Bird Survey indicated that grassland- and wetland-breeding bird species exhibited significant declines, whereas species exhibiting significant increases were those associated with human structures and woody vegetation. Population declines and increases for species with similar habitat associations paralleled breeding habitat changes, providing evidence that factors on the breeding grounds are having a detectable effect on breeding bird populations in the northern Great Plains.

Keywords: habitat, host species, abundance, North Dakota, Great Plains

Ingersoll, S. R. 1890. That cheeky cowbird. Ornithol. and Oologist 15:31.

Adds 17 host species to a previously published list.

Keywords: host species

Jackson, N. H. and D. D. Roby. 1992. Fecundity and egg-laying patterns of captive yearling brown-headed cowbirds. Condor 94:585-589.

Captive yearling cowbirds were monitored to assess individual annual fecundity, patterns of egg-laying, and clutch size. Results indicate that cowbirds are indeterminant layers, capable of daily egg production over extended periods with some individuals producing over 30 eggs in their first breeding season.

Keywords: fecundity

Jacobs, J. W. 1923. Cowbird (Molothrus ater ater) lays eggs direct from oviduct into the nest of its victim. Oologists Rec. 3:19-20.

The author proposes that cowbirds lay eggs directly into hosts nest, as opposed to carrying their eggs in their beaks.

Keywords: behavior

Jacobs, J. W. 1924. The other egg in the nest. Oologist 41:52-54.

Keywords: brood parasitism, host species

Jacobs, J. W. 1938. The eastern cowbird vs. the Kentucky warbler. Auk 55:260-262.

A first-person account of cowbird parasitism of Kentucky warbler nests over a 50-year period.

Keywords: host species

Jobin, B. and J. Picman. 1994. Artificial nest parasitized by a brown-headed cowbird, Molothrus ater. Can. Field-Nat. 108:482-484.

In 1989-1990, a cowbird egg was found in 1 of 1,532 artificial passerine nests constructed in 8 marshes and upland habitats in the Ottawa-Hull region. This is the first report of a cowbird parasitizing an artificial open-cup nest that lacked activity of the adults around the nest and signs of normal passerine egg-laying pattern. The authors suggest that this was an Aaccidental@ host choice by the cowbird.

Keywords: brood parasitism, egg manipulation

Johnson, D. M., G. L. Stewart, M. Corley, R. Ghrist, J. Hagner, A. Ketterer, B. McDonnell, W. Newsom, E. Owen, and P. Samuels. 1980. Brown-headed cowbird (Molothrus ater) mortality in an urban winter roost. Auk 97:299-320.

The authors studied cowbird mortality at a communal winter roost in live oak stands at the Rice University campus, Houston, Texas, from 1974-1976. A comparison of live (decoy-trapped) and dead cowbirds during 1976 indicated that adult males were over represented among the dead and that within each age class the dead males had significantly longer wings. Results suggest that mortality is related to depletion of winter food supplies, and that aggressiveness, a trait unrelated to size, was believed to play an important role in survival.

Keywords: mortality, Texas

Johnson, R. G. and S. A. Temple. 1990. Nest predation and brood parasitism of tallgrass prairie birds. J. Wildl. Manage. 54:106-111.

Predation and parasitism rates on five bird species nesting were studied in fragments of a Minnesota tallgrass prairie in 1983 and 1984. Rates were affected by the size of the prairie fragment containing the nest, the distance from the nest to a wooded edge, and the number of growing seasons since the vegetation around the nest had burned. Rates of nest predation for the five species were lower (P < 0.10 in each case) for nests on large (130 ha) fragments, in areas far (45 m) from a wooded edge, and in vegetation that was recently burned (3 yr). Rates of brood parasitism were lower (P < 0.10 in each case) for nests further from a wooded edge. Prairie management to maximize nest productivity should focus on providing large, regularly burned prairies, in the absence of wooded edges.

Keywords: habitat, Minnesota

Johnsrude, I. S., D. M. Weary, L. M. Ratcliffe, and R. G. Weisman. 1994. Effect of motivational context on conspecific song discrimination by brown-headed cowbirds (Molothrus ater). J. Comp. Psych. 108:172-178.

The authors conducted two experiments to examine the effects of motivational context on the perception of conspecific songs by brown-headed cowbirds. The first experiment involved eliciting female sexual displays using tape-playback of normal songs and rearranged sequences of the component phrases. In the second experiment, food was provided as an award to male and female cowbirds that were able to discriminate among songs. Similarities and differences in the results of the two experiments are discussed, with results suggesting that some aspects of cowbird song perception remain constant across motivational contexts, whereas others are unique to particular motivational contexts.

Keywords: vocalization, behavior

Johnston, B. J. 1957. A technique for trapping cowbirds. Wilson Bull. 69:278.

The author describes a trapping technique using a nest containing eggs as bait.

Keywords: population control, trapping

Johnston, R. F. 1960. Behavioral and ecologic notes on the brown-headed cowbird. Condor 62:137-138.

This article is a first-person observation of an Oregon junco feeding a cowbird fledgling in Berkeley, California, in 1958. The author describes the begging call of the cowbird and the vegetation surrounding the observation, and also cites previously published information.

Keywords: behavior, host species, California

Jones, F. M. 1941. The cowbird. Oologist 58:117.

A series of first-person accounts of a single cowbird parasitizing several species in Virginia. The female laid eight eggs between May 5 and June 15, 1941.

Keywords: fecundity, host species, Virginia

Kattan, G. H. 1995. Mechanisms of short incubation period in brood-parasitic cowbirds. Auk 112:335-342.

Under controlled laboratory conditions, the author attempts to determine why cowbird eggs exhibit accelerated rates of embryo development. The results of this study suggest that cowbird eggs may have a low energy content, which results in a short incubation period because yolk reserves are depleted earlier than that of their hosts eggs.

Keywords: shiny cowbird, eggs

Kattan, G. H. 1996. Growth and provisioning of shiny cowbird and house wren host nestlings. J. Field Ornithol. 67:434-441.

The author reports on the growth and provisioning rates of cowbird and host house wren nestlings in the Cauca Valley, Colombia. Results of the study indicate that the mass and provisioning rates of a single cowbird were equivalent to those of a brood of three wrens. The author concludes that due to a combination of rapid growth and early fledging, in conjunction with a short incubation period, cowbirds are able to out compete the host nestlings.

Keywords: shiny cowbird, host species, Columbia

Kattan, G. H. 1997. Shiny cowbirds follow the shotgun strategy of brood parasitism. Anim. Behav. 53:647-654.

House wren nests were monitored to determine if cowbirds exhibited the ability to synchronize their parasitism with that of the egg-laying hosts, and whether they avoid multiple parasitism. Although the author observed cowbirds monitoring the hosts nest throughout the nest building and egg-laying periods, the cowbirds did not synchronize their egg-laying with that of the host to any significant degree, and multiple parasitism was common. Shiny cowbirds appeared to follow a shotgun strategy; i.e., they rely more on high fecundity and chance than on the precise placement of each egg.

Keywords: shiny cowbird, host species, brood parasitism

Kebbe, C. E. 1954. Nesting record of the cowbird in western Oregon. Murrelet 35:51.

Cowbirds were observed by the author in the vicinity of Portland, Oregon, during the spring months of 1953 and 1954. He also observed a Cassins vireo nest that contained two vireo eggs and one cowbird egg in 1954.

Keywords: host species, range expansion, Oregon

Kedney. H. S. 1869. The cow bunting. Amer. Nat. 3:550.

A first-person account of multiple brood parasitism of a white-crowned sparrow and a pewee flycatcher in 1868.

Keywords: host species

Kellogg, C. D. 1900. Cowbird in a doves nest. Bird-Lore 2:121.

A first-person observation of cowbird parasitizing a doves nest in Pennsylvania, 1899. The cowbird young hatched, but the outcome was unknown.

Keywords: host species, Pennsylvania

Kells, W. L. 1885. Foster parents of the cowbird. Auk 2:106.

During the summer of 1884, the author discovered young cowbirds in the nests of the kingbird, house wren, and chipping sparrow.

Keywords: host species

Kelly, S. T. and M. E. DeCapita. 1982. Cowbird control and its effect on Kirtlands warbler reproductive success. Wilson Bull. 94:363-365.

From 1975-1981, the U.S. Fish and Wildlife Service conducted an intensive program of cowbird removal in an effort to increase the nesting success of the Kirtlands warbler in the lower peninsula of Michigan. This report summarizes the effectiveness of the program based on the nesting and fledging success of the warblers.

Keywords: population control, trapping, Michigan

Kendall, J. B. 1940. Cowbirds as home wreckers. Passenger Pigeon 2:73.

A first-person account of savannah sparrows and chipping sparrows rearing cowbird chicks in Wisconsin.

Keywords: host species, Wisconsin

Kennard, J. H. 1978. A method of local limitation of brood parasitism by the brown-headed cowbird. N. Amer. Bird Bander 3:100-101.

This paper is intended to demonstrate a practical method of reducing cowbird parasitism by trapping. The author suggests that the most effective means of control may involve the banding and release of males and the euthanizing of females.

Keywords: population control, trapping

Kessler, F., M. L. Giltz, and H. E. Burtt. 1967. High mortality of a population of cowbirds wintering at Columbus, Ohio. Ohio J. Sci. 67:46-50.

During two heavy rainfalls in Columbus, Ohio, in 1963-1964, a wintering population of cowbirds experienced high mortality. Their deaths were associated with a soaking of their feathers, and their inability to fly and to remain on their perches in the roost. Causes of death may be associated with the lowering of their body temperature, enhanced by bathing in streams containing detergents.

Keywords: mortality, Ohio

Keys, G. C., R. C. Fleischer, and S. I. Rothstein. 1986. Relationships between elevation, reproduction and the hematocrit level of brown-headed cowbirds. Comp. Biochem. Physiol. 83A:765-769.

The objectives of this study were to determine intra-populational (i.e., sex, age) variation in the hematocrit level of cowbirds and to examine the relationship between reproduction and hematocrit levels of cowbirds breeding at higher elevation. The study also attempted to determine the relationship between elevation and hematocrit in cowbirds. Data suggest that reproduction suppresses hematocrit, and females therefore must contend with a potentially lower rate of oxygen absorption.

Keywords: physiology

King, A. P. 1973. Some factors controlling egg laying in the parasitic cowbird (Molothrus ater). Amer. Zool. 13:1259.

As a part of an investigation into the behavioral development of the cowbird, 20 cowbirds (15 females and 5 males) were successfully bred in captivity, laying a total of 220 eggs over a 2-year period. Five factors were evaluated to determine their effects on host egg removal and subsequent parasitism. The results suggest that the size of the host egg is the primary deterrent of egg removal and brood parasitism. Abstract only.

Keywords: eggs

King, J. R. 1973. Reproductive relationships of the rufous-collared sparrow and the shiny cowbird. Auk 90:19-34.

While conducting other unrelated studies of the rufous-collared sparrow in northwestern Argentina, the author recorded data on the brood parasitism of this species by the shiny cowbird.

Keywords: shiny cowbird, host species, Argentina

King, A. P. and M. J. West. 1977. Species identification in the North American cowbird: appropriate responses to abnormal song. Science 195:1002-1004.

In this study, female cowbirds raised in auditory isolation from males responded to the songs of male cowbirds with copulatory postures. The songs of males reared in isolation were more effective in eliciting the female posture response than the songs of naturally reared males. The females were subjected to the songs of various species, but did not exhibit any response. These results suggest that song is the primary mechanism of species recognition for the cowbird.

Keywords: behavior, vocalization

King, A. P. 1979. Variables affecting parasitism in the North American cowbird (Molothrus ater). Ph.D. diss., Cornell University, Ithaca.

Keywords: brood parasitism

King, A. P., M. J. West, and D. H. Eastzer. 1980. Song structure and song development as potential contributors to reproductive isolation in cowbirds (Molothrus ater). J. Comp. Physiol. Psychol. 94:1028-1039.

The songs of two brown-headed cowbird subspecies (M. a. ater and M. a. obscurus) were studied in three ways: by comparisons of song variation, by developmental analyses of the role of species-typical stimulation in M. a. ater, and by tape-playback to captive females. The results indicate the presence of intraspecific variation. The findings suggest that song can act as a mechanism of selective mating and thus has the potential to affect reproductive isolation. The results also indicate the importance of song development in juvenile cowbirds.

Keywords: vocalization, behavior

King, A. P., M. J. West, D. H. Eastzer, and J.E.R. Staddon. 1981. An experimental investigation of the bioacoustics of cowbird song. Behav. Ecol. Sociobiol. 9:211-217.

The purpose of this study was to explore whether song potency changes with distance in the field. No field recordings elicited high levels of response by the females. When songs of known high potency are systematically degraded, the results indicate that female cowbirds are sensitive to small changes in signal-to-noise ratio and to atmospheric attenuation. Data suggest that cowbird song potency degrades very rapidly with distance in the field.

Keywords: vocalization

King, A. P. and M. J. West. 1983. Female perception of cowbird song: a closed developmental program. Developmental Psychobiology 16:335-342.

To investigate the modifiability of the brown-headed female cowbirds response to male song, the authors reared females with either M. a. ater or M. a. obscurus males, whose songs differ in geographic origin. The females were later tested for their responsiveness to playback of M. a. ater and M. a. obscurus song.

Keywords: vocalization

In an attempt to assess the acoustic elements that constitute song potency in cowbirds, a tape-playback experiment was conducted using the female cowbirds copulatory posture as a bioassay of song potency. The data demonstrate that the same semantic information may be mediated through different song structures for each of the two subspecies. These data reveal a new song parameter relying upon the operation of the cowbirds two voices that contribute to song potency.

Keywords: vocalization

King, A. P. and M. J. West. 1983. Epigenesis of cowbird songCa joint endeavor of males and females. Nature 305:704-706.

The role of social stimulation from female brown-headed cowbirds on male song learning was tested. Two studies using males of the eastern subspecies reared in complete isolation from male conspecifics were conducted. The results of this study establish a new, nonauditory source of vocal instruction: social stimulation from the songs intended recipient. Keywords: vocalization

Five metrics of song learning are described for brown-headed cowbirds. The intent of these metrics is to capture not only the behavior of the song learner, but the social context in which song learning occurs. In general, the results revealed by these metrics indicate that males learn to be effective singers by attending to the social consequences of their behavior.

Keywords: vocalization

King, A. P., M. J. West, and D. H. Eastzer. 1986. Female cowbird song perception: evidence for different developmental programs within the same subspecies. Ethology 72:89-98.

In Oklahoma, female brown-headed cowbirds near the subspecies border with M. a. obscurus were tested for their discrimination of songs from their native area and from Austin, Texas. Females captured in Oklahoma showed a strong preference for their native song variants. In contrast, captive females from Oklahoma who were housed with Austin males showed no preference, responding equally to Oklahoma and Austin song. The songs of the Austin males housed with the Oklahoma females did not differ acoustically from those of wild Austin males. Therefore, the results suggest that a different developmental pattern may function in this region than in eastern populations of M. a. ater.

Keywords: vocalization

King, A. P. and M. J. West. 1988. Searching for the functional origins of song in eastern brown-headed cowbirds. Anim. Behav. 36:1575-1588.

The authors conducted three experiments to examine the functional properties of vocal precursors to stereotyped song in socially housed captive brown-headed cowbirds. This paper reports on the acoustic origins of the different vocal outcomes. In addition, a winter roost of cowbirds was studied to investigate the setting in which males naturally develop song. The field data indicated that free roaming and laboratory-housed males shared the same structural categories of song and that the winter roost provided males with opportunities to interact with females. Results suggest that song ontogeny is a dynamic process involving social and vocal interactions between singers and listeners.

Keywords: vocalization

King, A. P. and M. J. West. 1989. Presence of female cowbirds affects vocal imitation and improvisation in males. J. Comp. Psychol. 103:39-44.

This article reports that imitation and improvisation of tutor songs by eastern male cowbirds differ when housed with conspecific females, as opposed to nonconspecifics. Males that were individually housed with females and tutored with 12 different song types, developed repertoires composed primarily of improvised and original song types. Males housed with canaries had repertoires composed entirely of copies from the tutor songs. The potency of the males repertoires, as tested by playback to females, appeared to be related to the song responsiveness of their female companions. The results add further evidence that suggests that male cowbirds configure their song repertoire by observing the social signals from companions.

Keywords: vocalization

King, J. R. 1954. Victims of the brown-headed cowbird in Whitman County, Washington. Condor 56:150-154.

The author lists some species parasitized by the brown-headed cowbird in this area.

Keywords: host species, Washington

Kingery, H. E. and P. R. Julian. 1971. Cassins sparrow parasitized by cowbird. Wilson Bull. 83:439.

A first-person observation of a Cassins sparrow being parasitized by a cowbird in 1970 in southeastern Colorado.

Keywords: host species, Colorado

Klaas, E. E. 1970. A population study of the eastern phoebe, Sayornis phoebe, and its social relationships with the brown-headed cowbird, Molothrus ater. Ph.D. diss. University of Kansas, Lawrence.

Keywords: host species, brood parasitism, Kansas

Klaas, E. E. 1975. Cowbird parasitism and nesting success in the eastern phoebe. University of Kansas Museum of Natural History 41:1-18.

In eastern Kansas from 1962-1965, 24% of the eastern phoebe clutches were parasitized by the brown-headed cowbird. Parasitized nests were less likely to fledge young phoebes than those that were not parasitized. Cowbird parasitism ranked second to predation as the leading causes of nest failure. Eastern phoebes are suitable, tolerant host for cowbirds, providing cowbirds with a 41.7% nesting success.

Keywords: host defense, host species

Klein, N. K. and K. V. Rosenberg. 1986. Feeding of brown-headed cowbird (Molothrus ater) fledglings by more than one "host" species. Auk 103:213-214.

A first-person report of individual fledgling cowbirds being fed sequentially by adults of two different species in Montana in 1978, on four occasions.

Keywords: host species, Montana

Klute, D. S. and R. J. Robel. 1997. Will conversion of Conservation Reserve Program (CRP) lands to pasture be detrimental for grassland birds in Kansas? Am. Midl. Nat. 137:206-212.

The authors compared avian use of CRP areas with that of active pastures to determine if conversion from CRP to pasture would be detrimental to grassland birds. Data on vegetative structure, avian abundance, and avian reproductive success were collected on five CRP fields and five pastures during the summer of 1993. Total avian abundance, including that of dickcissels, grasshopper sparrows, meadowlarks, brown-headed cowbirds, and upland sandpipers were greater in pastures than in CRP fields. Rates of nest parasitism by cowbirds did not differ between the habitats. Results indicate that in this region conversion probably would not be detrimental to grassland bird populations provided the land is moderately grazed.

Keywords: habitat, Kansas

Kozlovic, D. R., R. W. Knapton, and J. C. Barlow. 1996. Unsuitability of the house finch as a host of the brown-headed cowbird. Condor 98:253-258.

Cowbirds parasitized 99 (24.4%) of 406 finch nests observed at Barrie, Guelph, Orillia, and St. Catharines, Ontario, Canada, during the periods of 1983-1985 and 1990-1993. Hatching success of cowbird eggs was 84.8%, but no cowbirds successfully fledged, probably due to an insufficient diet. The authors conclude that nestling diet may be important in determining cowbird choice of host.

Keywords: brood parasitism, host species, diet, Ontario, Canada

Kren, J. 1995. Dimorphism in acceptance/rejection behavior of introduced model cowbird eggs among colonies of red-winged blackbird. Proc. Nebraska Acad. Sci. 105:29-30.

The objectives of this study were to determine what mechanisms maintain the ratio of two host behavioral phenotypes in various populations of blackbirds: Aacceptors,@ those which accept a parasitic egg, and Arejectors,@ those which reject a parasitic egg. From May through August 1994, the author experimented by artificially parasitizing blackbird nests.

Keywords: host defense, host species

LaFave, L. D. 1955. The unusual feeding of a young Nevada cowbird. Murrelet 36:25.

In the vicinity of Spokane, Washington, along the Little Spokane River, July 29, 1954, the author observed a young Nevada cowbird perched in a wild rose bush, being fed by a male Macgillivarys warbler. The author also noted that soon after being fed by the warbler, a female Merrills song sparrow appeared and again fed the young cowbird.

Keywords: host species, Washington

LaJeunesse, H. V. 1923. Dwarf cowbird nesting in Alameda County, California. Condor 25:31-32.

Beginning on May 23, 1922, the author discovered several nests of various host species which had been parasitized in Alameda County, California.

Keywords: host species, California

Larison, B., S. A. Laymon, P. L. Williams, and T. B. Smith. 1998. Song sparrow vs. cowbird brood parasites: impacts of forest structure and nest-site selection. Condor 100:93-101.

The reproductive ecology of the song sparrow in natural and restored riparian forest was studied to evaluate the influence of habitat structure and nest-site selection on cowbird parasitism. Results suggest that further research on the association of habitat structure, nest-site selection and cowbird parasitism could reduce parasitism rates and increase nest success of host species through appropriate long-term habitat management and restoration efforts.

Keywords: nest-site selection, habitat

Lanyon, S. M. 1992. Interspecific brood parasitism in blackbirds (Icterinae): a phylogenetic perspective. Science 225:77-79.

An 852-base pair region of the cytochrome-b gene was sequenced for cowbirds and 20 additional taxa of the new world blackbirds. The goals of this study were to determine whether interspecific brood parasitism is multiply derived within the assemblage, and to determine the nature of the evolutionary transformation between various forms of interspecific brood parasitism. Cladistic analysis of the sequence data indicates that brood parasitism evolved at a single time within the Icterinae. The primitive form of interspecific brood parasitism in this assemblage is host-specificity, with host-generality representing the derived condition.

Keywords: brood parasitism

Laskey, A. R. 1944. Cowbird data from a banding station. Migrant 15:17-18.

In an attempt to better understand the cowbirds mating habits and territorial behavior, 30 cowbirds (10 adult males, 11 adult females, and 9 immatures) were banded by the author between 1935 and 1943, near Nashville, Tennessee. Only four females and one male were recaptured in subsequent years.

Keywords: band recovery, mating system, territorial behavior, Tennessee

Laskey, A. R. 1945. Towhee-cowbird nesting data for 1945. Migrant 16:46.

This article is a first-person record of finding 10 red-eyed towhee nests containing 31 towhee eggs and 8 cowbird eggs in Tennessee.

Keywords: host species, Tennessee

Laskey, A. R. 1950. Cowbird behavior. Wilson Bull. 62:157-174.

A thorough overview of cowbird behavior, including songs and call notes, posturing and display, courtship, contentions for social dominance, pair formation, mating, social dominance of the pair, copulation, status of other resident cowbirds, territorial defense, and defense of mates was conducted by the author.

Keywords: behavior, mating system, social organization, vocalization

Laymon, S. A. 1987. Brown-headed cowbirds in California: historical perspectives and management opportunities in riparian habitats. Western Birds 18:63-70.

This paper documents the expansion in range of brown-headed cowbirds in California, discusses the means by which cowbirds can contribute to the extinction of their hosts, and provides recommendations to reduce cowbird parasitism on riparian species. By conducting a literature search and examining museum collections for nesting and specimen records of cowbirds in California west of the Sierra Nevada crest and the desert region north to Mono County, the author was able to establish the expansive range of the cowbird. National Audubon Society Christmas Bird Count records were reviewed and field surveys conducted by the author in an attempt to locate wintering cowbird concentrations in central California.

Keywords: brood parasitism, population control, range expansion, migration, California

Leathers, C. L. 1956. Incubating American robin repels female brown-headed cowbird. Wilson Bull. 68:68.

This article is a first-person account of a female robin actively defending her nest from a female cowbird in Lawrence County, Pennsylvania, 1954.

Keywords: host defense, host species, Pennsylvania

Lees, W. A. D. 1939. Song sparrow feeds five cowbirds. Can. Field-Nat. 53:121.

This paper is a first-person account of a song sparrow feeding five cowbirds in Alberta, Canada, 1939.

Keywords: host species, Alberta, Canada

Line, L. 1994. Curse of the cowbird. National Wildlife 32:40-45.

The author provides a detailed summary of the parasitic habits of the brown-headed cowbird and identifies sites of extensive cowbird research, including the Shawnee National Forest of southern Illinois, and Fort Hood Army Base, Texas.

Keywords: brood parasitism, population control, trapping, Illinois, Texas

Link, W. A. and D. C. Hahn. 1996. Empirical Bayes estimation of proportions with application to cowbird parasitism rates. Ecology 77:2528-2537.

The authors describe the application of the Empirical Bayes approach in the estimation of proportions, using data obtained from a community-wide study of brown-headed cowbird parasitism rates. Empirical Bayes estimates identify those species for which there is the greatest evidence of extreme parasitism rates. Subgroup analysis of the data on cowbird parasitism rates indicates that parasitism rates for the neotropical migrant group are no greater than those of resident/short-distance migrant species in a forested community. The data and analyses demonstrate that the parasitism rates for certain neotropical migrant species vary significantly.

Keywords: brood parasitism, host species

Linz, G. M. and S. B. Bolin. 1982. Incidence of brown-headed cowbird parasitism on red-winged blackbirds. Wilson Bull. 94:93-95.

This article is a first-person account documenting a 60% parasitism rate of red-winged blackbird nests during May and June 1979 in Cass County, North Dakota.

Keywords: brood parasitism, host species, North Dakota

Lown, B. A. 1980. Reproductive success of the brown-headed cowbird: a prognosis based on Breeding Bird Census data. American Birds 34:15-17.

This study was conducted to assess the ideal or typical cowbird/host ratio. Results indicate that the ratio of nesting cowbirds to available hosts is approximately 3/100. This ratio has remained constant over the last 40 years. The carrying capacity of cowbirds in any one area is controlled and limited by the total number of available host nests, and is therefore self-regulating over a large area.

Keywords: abundance, host species

Lowther, P. E. 1977. Old cowbird breeding records from the Great Plains Region. Bird-Banding 48:358-369.

Early breeding records were reviewed to compare the pattern of cowbird parasitism with more recent studies and to search for evidence of cowbird adaptation to particular host species within the Great Plains Region.

Keywords: brood parasitism, host species, Great Plains

Lowther, P. E. 1980. Gray catbirds rear brown-headed cowbirds. Inland Bird Banding 52:29-30.

This article consists of a first-person observation of four instances of catbirds successfully rearing cowbird chicks near Lawrence, Kansas, in 1980.

Keywords: host species, Kansas

Lowther, P. E. and S. I. Rothstein. 1980. Head-down or "preening invitation" displays involving juvenile brown-headed cowbirds. Condor 82:459-460.

This report is a summary of first-person observations of juvenile cowbirds engaging in the head-down display in Douglas County, Kansas, in 1979.

Keywords: behavior

Lowther, P. E. 1981. American robin rears brown-headed cowbird. J. Field Ornithol. 52:145-147.

This paper is a first-person account of a robin rearing a cowbird near Lawrence, Kansas, in 1980. The American robin is generally considered a poor host species due to its anti-parasitic behavior.

Keywords: host species, Kansas

Lowther, P. E. 1984. Catalog of brown-headed cowbird hosts from Kansas. Kansas Ornithol. Soc. Bull. 35:25-33.

Records from Friedmanns works (1929, 1963, 1971, 1977) are consolidated, and additional reports are added in this report. Overall, 48 species are listed in this catalog of potential cowbird hosts in Kansas. The appendix also lists 43 additional species of birds which breed in Kansas and have been recorded as cowbird hosts in states other than Kansas. Keywords: host species, Kansas

Lowther, P. E. 1984. Cowbird nest selection. Wilson Bull. 96:103-107.

The author compared cowbird nest selection with a regular Poisson distribution and found that nest selection by cowbirds is random.

Keywords: nest-site selection

Lowther, P. E. 1985. Catalog of brown-headed cowbird hosts from Iowa. Proc. Iowa Acad. Sci. 92:95-99.

A survey of literature, egg collections, and field data produced a list of 60 species that have served as cowbird hosts in Iowa.

Keywords: host species, Iowa

Lowther, P. E. 1993. Brown-headed cowbird. Birds of N. Amer. 47:1-24.

The author provides a summary of cowbird characteristics, distribution, systematics, migration, habitat, food habits, sounds, behavior, breeding, demography and populations, conservation and management, and appearance.

Keywords: behavior, distribution, morphology, life history, habitat, migration, diet

Lustick, S. 1970. Energy requirements of molt in cowbirds. Auk 87:742-746.

This study compares molting and nonmolting cowbirds over a temperature range of 5 to 40 ^oC, in an attempt to determine the amount of energy required for feather formation and the energy required for thermal regulation in thermal neutrality. Experimental birds were captured throughout 1968 in Los Angeles County, California. The results indicate that at temperatures below 35 ^oC an additive effect exists between the energy required for feather formation and that required for thermal regulation.

Keywords: molt, California

Luther, D. H. 1974. Observations at a Carolina wren nest from which brown-headed cowbirds fledged. Wilson Bull. 86:51-57.

This paper is a first-person detailed account of first-year wrens, a rare host, successfully fledging three cowbird chicks in Montgomery County, Indiana, in 1972.

Keywords: host species, Indiana

Luttringer, L. A. Jr. 1926. Tame cowbird. Oologist 43:114.

The author reports how an injured cowbird became so tame in Pennsylvania in 1926 that it did not try to escape and perched frequently on the authors head.

Keywords: behavior, Pennsylvania

Lyon, L. A. and D. F. Caccamise. 1981. Habitat selection by roosting blackbirds and starlings: management implications. J. Wildl. Manage. 45:435-443.

Blackbird and starling roost-site selection process was evaluated in mixed-species assemblages. The physical and vegetative characteristics of 25 roost sites in central New Jersey in 1977 were identified and recorded. Early successional stands of red maple and sweetgum were the primary sites selected for roosting. These stands typically supported high tree densities, low mean basal areas, and compact enclosed canopies. The age of the tree stand also influenced roost site selection. By evaluating the similarities between the roost sites, habitat management is suggested as a means of roost management.

Keywords: habitat, New Jersey

Lyon, B. E. and J. M. Eadie. 1991. Mode of development and interspecific avian brood parasitism. Behav. Ecol. 2:309-318.

In this study, the authors suggest that the association between the mode of development and the form of parasitism reflects a fundamental difference between altricial and precocial birds in the relative benefits of emancipation from parental care after egg laying. They propose that altricial brood parasites obtain such a large increase in realized fecundity by avoiding the costs of parental care that obligate parasitism is favored over facultative parasitism. The authors further suggest that facultative interspecific parasitism in birds may have originated through a carryover of intraspecific parasitism.

Keywords: brood parasitism, evolution

Lyon, B. E. 1997. Spatial patterns of shiny cowbird brood parasitism on chestnut-capped blackbirds. Anim. Behav. 54:927-939.

The author determined the individual spatial patterns of egg-laying female cowbirds by documenting the various egg morphs found in the host nests. By using egg dimensions and color patterns, the author was able to conclude that individual cowbirds often laid several eggs in the same colony; females laid their eggs in more than one colony; and several females laid eggs in each colony, and often in the same host nests. Based on these conclusions, cowbirds do not defend exclusive territories with respect to host nests.

Keywords: shiny cowbird, brood parasitism

Mason, P. 1986. Brood parasitism in a host generalist, the shiny cowbird: I. The quality of different species as hosts. Auk 103:52-60.

This study documents a wide range of host suitability in terms of their response to cowbird eggs, nestling diet, and nest survivorship. The author conducted cross-fostering experiments and recorded life history observations to determine that nestling cowbirds require a diet composed of animal protein. The suitability of a species to serve as a suitable cowbird host varies in respect to the hosts life history and anti-parasitic response to cowbirds near their nests.

Keywords: host species, shiny cowbird

Mason, P. 1986. Brood parasitism in a host generalist, the shiny cowbird: II. Host selection. Auk 103:61-69.

Host selection by shiny cowbirds was studied at two sites in Buenos Aires Province, Argentina from 1977 to 1979.

Keywords: host species, shiny cowbird, Argentina

Mason, P. and S. I. Rothstein. 1986. Coevolution and avian brood parasitism: cowbird eggs show evolutionary response to host discrimination. Evolution 40:1207-1214.

The objective of this study was to determine if the eggs of the shiny cowbird were enlarged as an evolutionary response to the rejection behavior exhibited by the rufous horneros. The typical eggs of the shiny cowbird are extremely variable in size, however the cowbird eggs found in the nests of this host were an average of 12% larger. The rufous horneros eject cowbird eggs with widths less than about 88% of the widths of their own eggs. The authors conclude, based on allometric analysis of egg width and volume, that the larger eggs laid in the nests of this host species is apparently an evolutionary response to selection exerted by the host species.

Keywords: host species, eggs, shiny cowbird

Mason, P. 1987. Pair formation in cowbirds: evidence found for screaming but not shiny cowbirds. Condor 89:349-356.

Sixty screaming cowbirds and 150 shiny cowbirds were trapped and banded in Buenos Aires Province, Argentina, in 1978 and 1979. Analysis of recaptures provides statistical evidence for pair formation in screaming cowbirds, but not shiny cowbirds, a result supported by observations of free-living birds. The author suggests that differences in host selection behavior may produce significant effects on other aspects of the species breeding biology.

Keywords: mating systems, band recovery, screaming cowbird, shiny cowbird, Argentina

Mariani, C. L., C. G. Earley, and C. McKinnon. 1993. Early nesting by the American goldfinch, Carduelis tristis, and subsequent parasitism by the brown-headed cowbird, Molothrus ater, in Ontario. Can. Field-Nat. 107:349-350.

A goldfinch nest was found on May 27, 1991, at Guelph, Ontario. Early completion of the prealternate molt of the female goldfinch may have been a contributing factor in stimulating early nesting and egg laying. Although the nest was parasitized by a cowbird, the cowbird chick failed to survive, probably as a result of the highly granivorous diet normally fed to goldfinch nestlings.

Keywords: host species, Ontario, Canada

Mark, D. and B. J. Stutchbury. 1994. Response of a forest-interior songbird to the threat of cowbird parasitism. Anim. Behav. 47:275-280.

To test whether an eastern forest-interior songbird, the hooded warbler, recognizes brown-headed cowbirds as a potential threat, a mount of a cowbird or a Veery control was presented to 25 incubating warbler females. Female warblers were significantly more aggressive towards the cowbird than the Veery model. The results suggest that warblers have developed the ability to recognize cowbirds as a potential threat to their nests, and that host aggression can evolve relatively quickly even for nonlearned behavior.

Keywords: host defense, host species

Marvil, R. E. and A. Cruz. July 1989. Impact of brown-headed cowbird parasitism on the reproductive success of the solitary vireo. Auk 106:476-480.

The reproductive interactions of the cowbird and the vireo in the foothills of the Rocky Mountains west of Boulder, Colorado, from 1984-1986 are observed and documented in this report. Parasitism rates of 48.7% were observed, with vireos accepting the cowbird eggs. Previous studies indicate that the parasitism rates on vireos are higher in the Western United States than in the Eastern United States, however no previous studies have reported parasitism rates as high as those observed in this study.

Keywords: host species, Colorado

Mason, P. 1980. Ecological and evolutionary aspects of host selection in cowbirds. Ph.D. thesis, University of Texas, Austin.

Keywords: host species, evolution

May, R. M. and S. K. Robinson. 1985. Population dynamics of avian brood parasitism. Amer. Nat. 126:475-494.

The primary purpose of this study was to evaluate the population dynamics of host-parasite relationships. In the first section, the authors discuss generalized parasites that utilize many different host species, and survey existing demographic data for instances of multiple-host brood parasitism. In the following section, they discuss the population dynamics of the more specialized case of a one-host/one-parasite association, and briefly discuss some possible instances of brood parasites that parasitize a single host species.

Keywords: brood parasitism

Mayfield, H. F. 1961. Cowbird parasitism and the population of the Kirtlands warbler. Evolution 15:174-179.

The author summarizes the decline of Kirtlands warbler populations, and partially attributes the decline to parasitism by the brown-headed cowbird.

Keywords: host species, brood parasitism

Mayfield, H. F. 1961. Vestiges of a proprietary interest in nests by the brown-headed cowbird parasitizing the Kirtlands warbler. Auk 78:162-167.

In this report the vestiges of the brown-headed cowbird suggest a proprietary interest in the Kirtlands warbler nests. These vestiges include: intently observing nest construction; inspecting the nests at various intervals; repeatedly removing warbler eggs and not its own; never completely emptying the nest; and destroying several warbler eggs when the nest becomes crowded.

Keywords: behavior, brood parasitism, host species

Mayfield, H. 1965. Chance distribution of cowbird eggs. Condor 67:257-263.

Nine studies of host species were examined; in five of these studies, the distribution of cowbird eggs was nearly random as shown by comparison with a Poisson series. In eight studies, the distribution of subsequent cowbird eggs in each nest was nearly random. The author suggests that the appearance of nonrandomness found in some studies may be a result of sampling error caused by the human observers failure to find nests that had been abandoned early in the nesting cycle due to the presence of a cowbird egg.

Keywords: nest-site selection, Michigan

Mayfield, H. 1965. The brown-headed cowbird, with new and old hosts. Living Bird 4:13-28.

As the range of the brown-headed cowbird expands, eastern forest passerine species that have not developed anti-parasitic responses, are often parasitized and accept the presence of cowbird eggs and chicks. In contrast, the birds of the western grasslands have developed anti-parasitic tactics and are much less tolerant of parasitism by the cowbird. Intermediate in receptivity are the birds of the grassland edge, where these species have been only partially exposed to cowbird parasitism over time. The cowbirds success with its new eastern hosts has likely attributed to the increase in cowbird populations and continued northeastward and southeastward range expansion into areas of marginal suitability. The author suggests that new host populations may be subject to decline, at least at the local level, as cowbird numbers continue to increase.

Keywords: evolution, host species

Mayfield, H. 1977. Brown-headed cowbird: agent of extermination? American Birds 31:107-113.

In this report the author discusses the natural-system view of parasitism and the invader position towards cowbirds.

Keywords: brood parasitism

Mayfield, H. 1977. Brood parasitism - reducing interactions between Kirtlands warblers and brown-headed cowbirds. Pages 89-91 in S. A. Temple (ed.). Endangered birds. University of Wisconsin Press, Madison, Wisconsin.

The author provides a detailed account in the dramatic decline of a local Kirtlands warbler population and how cowbird trapping has aided in its recovery.

Keywords: host species, population control, trapping

McDaniel, J. W. and K. C. Goist. 1974. Color discrimination in cowbirds. Bird Watch 2:3-4.

In a attempt to determine whether cowbirds were able to distinguish between colors, the author conducted experiments using 19 male and 20 female captive cowbirds obtained from the Michigan Department of Natural Resources. The subjects were deprived of food and placed in cages where food was given as a reward for pushing one of two colored buttons. The results indicate that cowbirds do demonstrate the ability to discriminate colors.

Keywords: physiology, Michigan

McGeen, D. S. and J. J. McGeen. 1962. Catbird pair accepts cowbird egg and apparently raises young cowbird. Auk 79:116-117.

The authors document a catbird pair rearing a juvenile cowbird in Michigan.

Keywords: host species, Michigan

McGeen, D. S. and J. J. McGeen. 1968. The cowbirds of Otter Lake. Wilson Bull. 80:84-93.

The authors conduct a study on 55 acres near Pontiac, Michigan, in 1950 and record their findings and inferences as to the number of female cowbirds present, the size of clutches, number of cowbird eggs laid, the length and peak of the laying seasons, hosts species, and range covered by cowbirds.

Keywords: brood parasitism, fecundity, host species, Michigan

McGeen, D. S. 1971. Factors affecting cowbird success with yellow warbler and song sparrow hosts. Jack-Pine Warbler 49:53-57.

This report discusses parasitism by the brown-headed cowbird on a 50-pair colony of nesting yellow warblers and on smaller numbers of song sparrows and Traills flycatchers. The 55-acre study site was an old pasture, early in its successional stages and a low, wet thicket bordering a canal connecting Cass and Otter Lakes just west of Pontiac, Oakland County, Michigan. This report identifies the factors affecting cowbird success when parasitizing warbler and sparrow host species.

Keywords: brood parasitism, host species, Michigan

McGeen, D. S. 1972. Cowbird-host relationships. Auk 89:360-380.

This article is the third in a continuing series of reports on the relationships between brown-headed cowbirds and their hosts. This report uses the presence of multiple cowbird eggs as indicators of the cowbirds relationship with the song sparrow and the yellow warbler. The results suggest that brood parasitism on these two species is a well-regulated homeostatic mechanism.

Keywords: host species

McKay, C. R. 1994. Brown-headed cowbird in Strathclyde: new to Britain and Ireland. Brit. Birds 87:284-288.

This report documents the first record of a brown-headed cowbird in Europe at Ardnave Point, Islay, Strathclyde.

Keywords: range expansion, Britain, Ireland

McLaren, P. L. 1973. Physical combat in the brown-headed cowbird. Wilson Bull. 85:342-343.

The author records the unusual behavior of two male cowbirds engaged in physical combat in Pittsburgh, Pennsylvania, on April 18, 1972.

Keywords: behavior, Pennsylvania

McMaster, D. G. and S. G. Sealy. 1997. Host-egg removal by brown-headed cowbirds: a test of the host incubation limit hypothesis. Auk 114:212-220.

The objectives of this study was to test the hypothesis that female cowbirds deliberately remove host eggs to reduce the parasitized clutch volume to a size that the host can effectively incubate, ensuring that the cowbird egg will hatch. This was conducted by comparing nests where one or no host eggs were removed. Results indicate that neither incubation period, hatching spread, nor hatching order was significantly influenced by egg removal. Therefore, the removal of a host egg was not necessary for successful hatching of cowbird eggs in warbler clutches in all years, however it may increase hatching success in some years.

Keywords: brood parasitism

McMaster, D. G. and S. G. Sealy. 1998. Short incubation periods of brown-headed cowbirds: how do cowbird eggs hatch before yellow warbler eggs? Condor 100:102-111.

This study was conducted to determine if cowbird eggs hatch before yellow warbler eggs due to prolonged incubation of host eggs, a more rapid embryonic development of the cowbird egg, or due to some stimuli from the hosts eggs. The authors tested these hypotheses by comparing the incubation periods of cowbird eggs incubated in natural nests, incubated artificially in isolation from other eggs, and incubated artificially in clutches of yellow warbler eggs. The results suggest that in addition to rapid embryonic development, cowbirds hatch before many hosts by disrupting the incubation of the smaller host eggs, and possibly hatching early in response to stimuli from host eggs.

Keywords: eggs

Meanley, B. and W. C. Royall, Jr. 1976. Nationwide estimates of blackbirds and starlings. Pages 39-40 in Proc. bird control seminar. Bowling Green State University, Bowling Green.

Based on the national cooperative blackbird/starling winter roost survey conducted by the U.S. Fish and Wildlife Service during the winter of 1974-75, brown-headed cowbirds comprised 18% of 538 million blackbirds and starlings.

Keywords: range expansion

Mehlman, D. W. 1995. Notes on the increase of the brown-headed cowbird in New Mexico. NMOS Bull. 23:59-63.

This report summarizes information from the North American Breeding Bird Survey on the recent abundance and distribution of the cowbird in New Mexico.

Keywords: abundance, distribution, range expansion

Mengel, R. M. and M. A. Jenkinson. 1970. Parasitism by the brown-headed cowbird on a brown thrasher and a catbird. Wilson Bull. 82:74-78.

The authors report their observations of parasitism by a cowbird on a brown thrasher. They also include some brief notes on the parasitized nest of a catbird.

Keywords: host species

Mermoz, M. E. and J. C. Reboreda. 1994. Brood parasitism of the shiny cowbird, Molothrus bonariensis, on the brown-and-yellow marshbird, Pseudoleistes virescens. Condor 96:716-721.

The authors studied the relationship between the shiny cowbird and this particular host. Seventy-four percent of the brown-and-yellow marshbird nests found had been parasitized. Shiny cowbird parasitism reduced the nesting success of the marshbird mainly by puncturing or cracking the host eggs. Although the shiny cowbird chicks were physically smaller than that of their host, they were not out-competed for food. The marshbird appears to be a very suitable host for the cowbird, and is capable of rearing up to four cowbird chicks in a nest. The authors also compare the nesting success of the cowbird in marshbird nests with its nesting success in the other sympatric hosts.

Keywords: shiny cowbird, host species, brood parasitism

Mermoz, M. E. and J. C. Reboreda. 1996. New host for a specialized brood parasite, the screaming cowbird. Condor 98:630-632.

In this paper, the authors report on the screaming cowbird parasitism of the brown-and-yellow marshbird in an area also inhabited by the bay-winged cowbird, and document the successful rearing of screaming cowbird chicks by marshbirds.

Keywords: screaming cowbird, host species

Merrill, J. C. 1877. Notes on Molothrus aeneus. Bull. Nuttall Ornithol. Club 2:85-87.

The author presents a series of observations on brood parasitism and life history of the bronzed cowbird.

Keywords: bronzed cowbird, behavior, life history

Michael, C. W. 1935. Cowbirds appear in Yosemite. Condor 37:178.

This paper is a first-person account of the first recorded observation of cowbird parasitism in the Yosemite Valley, California, in 1934.

Keywords: range expansion, California

Middleton, A. L. A. 1986. The urban environment and its potential as a refuge from brood parasitism by the brown-headed cowbird. Congressus Internationalis Ornithologici 19:1802-1808.

The author analyzes the impacts of cowbird parasitism on nesting populations of the American goldfinch and chipping sparrow in urban and nonurban habitats. Results indicate that despite the high incidence of brood parasitism in the city, city nests had a higher success (47%) than campus nests (27%). The relationship between urban habitats and cowbird parasitism remains poorly understood.

Keywords: host species, habitat

Middleton, A. L. A. 1991. Failure of brown-headed cowbird parasitism in nests of the American goldfinch. J. Field Ornithol. 62:200-203.

Brown-headed cowbirds parasitized 47 of 802 goldfinch nests at Guelph, Ontario, between 1968 and 1989, however cowbird eggs hatched in only 13 of them and all nestlings died, probably due to an insufficient diet.

Keywords: host species, mortality, Ontario, Canada

Miles, D. B. May 1986. A record of brown-headed cowbird (Molothrus ater) nest parasitism of rufous-crowned sparrows (Aimophila ruficeps). Southwestern Nat. 31:253-254.

The author reports on the observation of a sparrow feeding a cowbird fledgling 20 km northeast of Tucson, Arizona, in 1981.

Keywords: brood parasitism, host species, Arizona

Miller, A. H. 1948. White-winged junco parasitized by cowbird. Condor 50:92.

Keywords: host species

Miller, L. E. 1917. Field notes on Molothrus bonariensis and M. badius. Bull. Amer. Mus. Nat. Hist. 37:579-592.

Copies of field notes taken during the American Museum of Natural Historys recent expedition to Bolivia and northwestern Argentina in 1915 are presented in this report.

Keywords: brood parasitism, shiny cowbird,

Mills, A. M. 1987. Size of host egg and egg size in brown-headed cowbirds. Wilson Bull. 99:490-491.

The author reports on the results of a study aimed at determining whether cowbird egg size varies as a function of host egg size. There was no indication of a correlation between the estimated volumes of cowbird and host eggs, nor was there any correlation between cowbird egg volume and host weight.

Keywords: eggs

Mills, A. M. 1988. Unsuitability of tree swallows as hosts to brown-headed cowbirds. J. Field Ornithol. 59:331-333.

The author artificially parasitized 15 swallow nests at Magnetawan, Ontario, in 1986 with the eggs of brown-headed cowbirds. Swallow hatching success was relatively high with 63 of 66 host eggs hatching. Seven cowbird hatchlings died, whereas six of the seven swallow pairs each fledged the cowbirds four swallow nest-mates. The cowbirds grew more slowly than cowbird nestlings in naturally parasitized nests of more typical hosts. Tree swallows appear to be unsuitable cowbird hosts during both incubation and nestling periods.

Keywords: brood parasitism, host species, egg manipulation

Mills, W. J. 1957. Summer range of cowbirds in the Atlantic Provinces. Nova Scotia Mus. Sci. Newsletter 2:25-27.

The author presents a summary of the expanding summer range of the brown-headed cowbird northward into Canada.

Keywords: range expansion, Canada

Mills, W. J. 1958. Cowbirds breed in Prince Edward Island. Can. Field-Nat. 72:170.

The author documents the first two breeding records of cowbirds in this area in 1953 and 1954.

Keywords: range expansion, Prince Edward Island, Canada

Monk, H. C. 1936. Cowbird nesting records for Davidson County. Migrant 7:32-33.

This article describes 28 observations of cowbird parasitism affecting 13 species in Davidson County, Tennessee.

Keywords: host species, Tennessee

Monroe, B. L. Jr. 1937. A cowbirds error. Migrant 8:38.

The author describes the discovery of two cowbird eggs in an abandoned red-eyed vireo nest on May 9, 1937.

Keywords: behavior

Monroe, B. L. Jr. 1957. A breeding record of the cowbird for Florida. Florida Nat. 30:124.

The author presents reports confirming cowbird breeding in Florida in 1956 and 1957.

Keywords: range expansion, Florida

Montgomery, R. A. 1979. Round-trip journey of a brown-headed cowbird. N. Amer. Bird Bander 4:109.

A first-person account of a 1971 recovery of a male cowbird in Wisconsin that had been previously banded in Illinois, and then recaptured in Illinois in 1972.

Keywords: band recovery, movement, Illinois, Wisconsin

Moore, G. A. 1928. A possible relationship between Bells vireo and the cowbird. Wilson Bull. 40:197.

A first-person account of a pair of vireos apparently deserting and rebuilding a total of ten nests in an effort to avoid incubating parasitic cowbird eggs in 1927.

Keywords: host defense, host species

Moore, T. 1956. Cowbird parasitism on a brown thrasher. Auk 73:558.

This paper is a first-person account of a brown thrasher feeding a cowbird chick near St. Paul, Minnesota, in 1943.

Keywords: host species, Minnesota

Morden, J. A. 1884. Cowbirds in a black and white creepers nest. Auk 1:193-194.

This paper is one of the first accounts of cowbird parasitism on creeper nests. It also documents the parasitism of indigo bunting nests in 1881.

Keywords: host species

Morris, D. L. 1996. Feeding habitat use and foraging behavior of the brown-headed cowbird (Molothrus ater). M.S. thesis, University of Missouri, Columbia.

In an effort to determine if habitat use or foraging behavior of cowbirds is related to invertebrate abundance, the author studied foraging cowbirds and observed their feeding habitat preferences and foraging success. The author further evaluated the relationships between environmental variables such as flock size, date, time of day, distance to cover, and number of cattle. To assess foraging success, data including cowbird foraging time, number of pecks, vigilance, and aggression were also recorded. Cowbird flock sizes, densities, peck rates, foraging time, vigilance, and aggression were recorded on seven sites in central Missouri where agriculture and forest habitats are highly interspersed. Invertebrate samples were also collected from the study sites to compare invertebrate biomass and density among treatments sites. The author concludes that foraging cowbirds prefer feedlots and short, grazed grass because both offer abundant, although different, food resources. It was also determined that although cowbird foraging behavior was highly variable between the sites, it was most influenced by the size of the cowbird flock and livestock herd.

Keywords: behavior, diet, habitat, Missouri

Murphy, M. T. 1986. Brood parasitism of eastern kingbirds by brown-headed cowbirds. Auk 103:626-628.

In this study, the author estimates cowbird brood parasitism rates on eastern kingbirds. Annual variation in the parasitism rates are also considered. The author discusses the impacts of parasitism on kingbirds and tests whether female cowbirds are selective of their host based on the size of the host egg. This study was conducted in Erie County, New York, in 1979, and in Douglas County, Kansas, in 1980 to 1983.

Keywords: brood parasitism, host species, New York, Kansas

Neff, J. A. 1926. Misplaced foster devotion. Bird-Lore 28:334-335.

This is a first-person account of cowbirds fledging from orchard oriole and towhee nests in 1924 in Missouri.

Keywords: brood parasitism, host species, Missouri

Nero, R. W. 1949. Baltimore oriole and young cowbird. Passenger Pigeon 11:132.

On June 25, 1949, the author observed a female oriole attempting to feed a fledgling cowbird in the middle of a road in the University Arboretum. The oriole offered what appeared to be an earthworm to the cowbird. The cowbird chick repeatedly dropped the worm, either rejecting the worm, or being unable to properly seize it.

Keywords: host species

Neudorf, D. L. and S. G. Sealy. 1992. Reactions of four passerine species to threats of predation and cowbird parasitism: enemy recognition or generalized responses? Behaviour 123:84-105.

Four host species of the brown-headed cowbird were exposed to taxidermic mounts of a female cowbird during their egg-laying or nestling stage. Responses of three rejector species toward the cowbird model did not vary over the nesting cycle, indicating that they do not recognize cowbirds as a unique threat. Considerable interspecific variability exists among the four species in defensive behaviors, which may reflect their different nesting habitats.

Keywords: behavior, host defense, host species

Neudorf, D. L. and S. G. Sealy. 1994. Sunrise nest attentiveness in cowbird hosts. Condor 96:162-169.

One hundred forty nests of 10 potential cowbird host species (6 Aacceptors@ and 4 Arejectors@ of cowbird eggs) at Delta Marsh, Manitoba, were observed at sunrise to determine if hosts are present on or near their nests when cowbirds attempt to parasitize their nests. The authors found no direct correlation between the frequency of parasitism of acceptor hosts and nest attentiveness. Also, no significant difference between acceptors and rejectors in early-morning vigilance was observed. The authors suggest that host species roosting on their nest may be the best means to guard against parasitism, but may not always prevent it.

Keywords: brood parasitism, host species, behavior, Manitoba, Canada

Nice, M. M. 1936. The cowbird as a subject of study. Wilson Bull. 48:60.

In Columbus, Ohio, cowbirds parasitized 26% to 77% of the early song sparrow nests studied over a 5-year period. In 1930-1931, the ratio of female cowbirds to their suitable host was approximately 1:11.5, however by 1934 and 1935 the ratio had decreased to 1:8.6 pairs of suitable hosts.

Keywords: abundance, host species, Ohio

Nice, M. M. 1937. Curious ways of the cowbird. Bird-Lore 39:196-201.

In this report the author discusses the habits of the brown-headed cowbird.

Keywords: behavior

Nice, M. M. 1939. Observations on the behavior of a young cowbird. Wilson Bull. 51:233-239.

A first-person observation of a nestling brown-headed cowbird's behavior after being removed from its hosts nest in Augusta, Michigan, in 1939.

Keywords: behavior, Michigan

Nice, M. M. 1941. Robins and cowbird eggs. Bird-Banding 12:33-34.

The author describes an experimental parasitism study to see if robins accepted foreign eggs in Illinois. Two of the eggs were rejected and five accepted.

Keywords: host defense, host species, egg manipulation, Illinois

Nice, M. M. 1949. The laying rhythm of cowbirds. Wilson Bull. 61:231-234.

This report discusses the laying pattern of four species of cowbirds that lay in clutches at intervals lasting from 5 to 8 days, and possibly longer. Eggs may be laid at daily intervals or 1-2 days may be skipped.

Keywords: fecundity, laying rate, eggs

Nickell, W. P. 1955. Notes on cowbird parasitism on four species. Auk 72:88-92.

This report briefly outlines the published records and the authors own observations for cowbird parasitism in four host species.

Keywords: host species, Michigan

Nickell, W. P. 1958. Brown-headed cowbird fledged in nest of catbird. Wilson Bull. 70:286-287.

This paper is a first-person account of a gray catbird raising and defending a cowbird chick in 1957 in Essex County, Ontario.

Keywords: host species, Ontario, Canada

Niemuth, N. D. and M. S. Boyce. 1997. Edge-related nest losses in Wisconsin pine barrens. J. Wildl. Manage. 61:1234-1239.

In this study, the predation of artificial nests in pine barrens savanna patches in northwestern Wisconsin was correlated significantly with proximity to edge (P0.02). Results indicate that the densities of blue jays and brown-headed cowbirds were significantly greater along edge transects than within savanna interior transects (P<0.001 and P0.001). The authors conclude that land management practices in the pine barrens may influence edge-related nest loss through predation and parasitism.

Keywords: predation, habitat, Wisconsin

Nolan, V. Jr. and C. F. Thompson. 1978. Egg volume as a predictor of hatchling weight in the brown-headed cowbird. Wilson Bull. 90:353-358.

The authors present a means to predict the weight and probably the overall body size of a cowbird nestling by correlating the cowbird eggs length and breadth. Since recent studies suggest that these correlations can vary dramatically among species, the authors contend that their results may have limited application in the field.

Keywords: eggs

Norman, R. F. and R. J. Robertson. 1975. Nest-searching behavior in the brown-headed cowbird. Auk 92:610-611.

In this report, the author describes three distinct types of cowbird nest-searching behavior observed while conducting field studies at Kingston, Ontario, from 1970 to 1973.

Keywords: behavior, Ontario, Canada

Norris, R. T. 1944. Notes on a cowbird parasitizing a song sparrow. Wilson Bull. 56:129-132.

The author summarizes observations of egg laying (six instances) and of egg removal (eight instances) by the cowbird.

Keywords: host species, egg laying

Norris, R. T. 1947. The cowbirds of Preston Frith. Wilson Bull. 59:82-103.

In this article the author provides a summary of many observations on cowbird behavior and nest parasitism within a 90-acre area near Butler, Pennsylvania.

Keywords: behavior, brood parasitism, Pennsylvania

Nyhof, M. 1990. The brown-headed cowbird: villain or survivor? Victoria Nat. 47:16-17.

The author gives a brief summary of the cowbirds effect on the survival of several species of songbird.

Keywords: brood parasitism, host species

O'Conner, R. J. and J. Faaborg. 1992. The relative abundance of the brown-headed cowbird (Molothrus ater) in relation to exterior and interior edges in forests of Missouri. Missouri Acad. Sci. 26:1-9.

Using censuses data collected at varying distances from the forest edge and from the edges of openings within the forest interior, the authors discovered a significant decrease in the relative abundance of cowbirds as the distance from forest edge increased. The density of cowbirds within the forest interior openings was positively correlated with the size of the opening.

Keywords: habitat, Missouri

O'Loghlen, A. L. and S. I. Rothstein. 1993. An extreme example of delayed vocal development: song learning in a population of wild brown-headed cowbirds. Anim. Behav. 46:293-304.

To determine whether vocal ontogeny in migratory cowbirds was open at 1 year of age, the authors recorded two kinds of songs from recently captured birds which had been given testosterone implants. The authors predicted that delayed learning in yearlings would occur since juveniles would have little opportunity to hear conspecifics during their hatching year. The study results offer further evidence for plasticity in the timing of learning, and suggest more variation than was previously believed in the vocal ontogeny of some oscines as a result of delayed opportunity to learn.

Keywords: vocalization, California

O'Loghlen, A. L. 1995. Delayed access to local songs prolongs vocal development in dialect populations of brown-headed cowbirds. Condor 97:402-414.

To determine how typical the region results from a previous study (OLoghlen and Rothstein 1993) were, the author compared adult and yearling vocal behavior in the Convict dialect adjacent to the Mammoth and the Round Valley dialect, 55 km south and 900 m lower in elevation. The author proposes a scheme for vocal development in Sierra Nevada populations of cowbirds and discusses possible reproductive consequences as a result of delayed vocal learning.

Keywords: vocalization, California

OLoghlen, A. L. and S. I. Rothstein. 1995. Culturally correct song dialects are correlated with male age and female song preferences in wild populations of brown-headed cowbirds. Behav. Ecol. Sociobiol. 36:251-259.

In a study of dialect populations of cowbirds, estradiol-implanted females from two dialects held the precopulatory lordosis posture longer in response to the local flight whistle song playback than to foreign whistle types. This is the first study to provide evidence of discrimination by female cowbirds based on flight whistle type. Evidence is presented from one of the study dialects that the majority of yearling male cowbirds are vocally distinct from resident adults in having either foreign or incomplete local whistles. The correlation between female whistle preference and male mating success suggests that the ability of males to generate the correct local whistle type may be influential when females assess the age and quality of a potential mate.

Keywords: behavior, vocalization

Olson, A. A. 1943. Cowbird carrying away and eating a birds egg in the evening. Wilson Bull. 55:195.

A first-person observation of a cowbird eating an egg probably taken from a hosts nest in Michigan in 1943 is summarized in this article.

Keywords: behavior, predation, Michigan

Ord, G. 1836. Observations on the cow bunting of the United States of America. Mag. Nat. Hist. 9:57-71.

This early report consists of first-person observations of cowbird parasitism on several species. These observations are used to disprove some earlier assumptions about cowbird behavior.

Keywords: behavior, host species

Orians, G. H., E. Roskaft, and L. D. Beletsky. 1989. Do brown-headed cowbirds lay their eggs at random in the nests of red-winged blackbirds? Wilson Bull. 101:599-605.

By analyzing the weekly distributions of numbers of eggs laid in the nests of potential hosts with Poisson distributions, the authors tested the hypothesis that female cowbirds deposit their eggs randomly in the nests of red-winged blackbirds at the Columbia National Wildlife Refuge in Washington from 1977 to 1983. The hypothesis that females laid randomly could not be rejected in any weekly period, however, when all data were pooled, a random hypothesis could be rejected because there were more nests without cowbird eggs than expected. Among parasitized nests, the random hypothesis was also rejected.

Keywords: brood parasitism, host species, Washington

Ortega, C. P. 1991. Ecology of blackbird/cowbird interactions in Boulder County, Colorado. Ph.D. diss., University of Colorado, Boulder.

The breeding biology of red-winged blackbirds and yellow-headed blackbirds was investigated in Boulder County, Colorado, from 1984 through 1986. Cowbird parasitism rates on red-winged blackbirds ranged from 5.1% to 12.7% throughout the years of study, with local variation ranging from 0 to 40%. Breeding parameters were investigated and experiments were conducted with both species of blackbirds to develop possible explanations for the lack of parasitism on yellow-headed blackbirds. The variation in breeding characteristics between the two blackbird species is believed to contribute to the variability in parasitism rates.

Keywords: host species, brood parasitism, Colorado

Ortega, C. P. and A. Cruz. 1991. A comparative study of cowbird parasitism in yellow-headed blackbirds and red-winged blackbirds. Auk 108:16-24.

The authors compared the breeding habits and behavior of yellow-headed blackbirds and red-winged blackbirds from 1985 through 1986 in Boulder County, Colorado, in an effort to develop possible explanations for the lack of cowbird parasitism on the yellow-headed blackbirds. Nest initiation by the yellow-headed blackbird peaked earlier than red-winged blackbirds. However, nest abandonment of active yellow-headed nests was dramatically higher at the end of the season than red-winged, and nestlings were more heavily parasitized with mites than were red-winged nestlings.

Keywords: host species, brood parasitism, Colorado

Ortega, C. P. and A. Cruz. 1992. Differential growth patterns of nestling brown-headed cowbirds and yellow-headed blackbirds. Auk 109:368-376.

The growth of nestling blackbirds and cowbirds, experimentally cross-fostered into blackbird nests, in Boulder County, Colorado, during the 1986 breeding season was monitored throughout this study. The weight, tarsometatarsus length, culmen length, gape width, and length of ninth primary for each individual were recorded. In order to calculate proportions of the adult weight attained by nestlings, the authors measured that of adult museum specimens. Study results indicate that brown-headed cowbirds attained a greater proportion of their adult weight and adult ninth-primary length by fledging age than did yellow-headed blackbirds. Female yellow-headed blackbirds attained a greater proportion of their adult weight and adult ninth-primary length by fledging age than did their male siblings. Keywords: growth rate, host species, Colorado

Ortega, C. P. and A. Cruz. 1992. Gene flow of the obscurus race into the north-central Colorado population of brown-headed cowbirds. J. Field Ornithol. 63:311-317.

By conducting a literature search and examining museum collections, the authors have determined that the northwestern race, artemisiae, has been the most abundant race in Colorado, with the eastern race, ater, more prevalent in the eastern portion of the state. The finding of yellow-flanged nestlings and obscurus adults in Boulder County, Colorado, in 1985 and 1986 indicates a range expansion of obscurus into Colorado.

Keywords: range expansion, Colorado

Ortega, C. P., J. C. Ortega, and A. Cruz. 1994. Use of artificial brown-headed cowbird eggs as a potential management tool in deterring parasitism. J. Wildl. Manage. 58:488-492.

In this study the authors added artificial and real cowbird eggs to red-winged blackbird nests in 1985 and 1991 to determine whether egg addition would affect subsequent nest parasitism. Results indicate that cowbirds avoided parasitizing nests which had been artificially parasitized, suggesting that the addition of cowbird eggs to blackbird nests may deter future parasitism. For endangered host species, the addition of artificial or real inviable cowbird eggs could prove to be an effective management tool.

Keywords: brood parasitism, eggs, population control, egg manipulation

Ortega, C. P., J. C. Ortega, S. A. Backensto, and C. A. Rapp. 1996. Improved methods for aging second-year and after-second-year male brown-headed cowbirds. J. Field Ornithol. 67:542-548.

The color of the underwing coverts, which indicates prebasic molt, was recorded from banded males during the summers of 1993-1995 The authors suggest that totally dark underwing coverts, at least in this population, may not be a reliable trait for distinguishing ASY from SY males as previous studies have suggested. If the underwing coverts are light gray, the cowbird can safely be assumed to be SY (or first year if before the second summer). However, if the underwing coverts of the cowbird are totally dark, the presence of brown in the primaries may be used to distinguish SY males.

Keywords: morphology

Ortega, C. P. and A. Cruz. 1998. Mechanisms of egg acceptance by marsh-dwelling blackbirds. Condor 90:349-358.

Keywords: eggs

Ortega, J. C., J. C. Ortega, C. P. Ortega, and A. Cruz. 1993. Does brown-headed cowbird egg coloration influence red-winged blackbird responses towards nest contents? Condor 95:217-219.

The purpose of these experiments was to investigate whether blackbirds use tactile or visual cues to discriminate among objects placed into their nests. Data suggest blackbirds discriminate using only tactile cues, however it cannot be definitively concluded. This article reports on the potential importance of cowbird egg coloration and maculation in the acceptance or rejection of various objects into the nests of red-winged blackbirds. This study was conducted in Boulder County, Colorado, in 1991.

Keywords: brood parasitism, Colorado

Packard, F. M. 1936. A black-capped chickadee victimized by the eastern cowbird. Bird- Banding 7:129-130.

On May 25, 1936, a black-capped chickadees nest, containing four chickadee eggs and two cowbird eggs, was found in a nesting box at the Austin Ornithological Research Station at North Eastham, Massachusetts. Two chickadee eggs hatched, but did not survive, and the two cowbird chicks were removed for study.

Keywords: host species, Massachusetts

Parks, R. A. 1950. Cowbird breeding in Atlanta. Oriole 15:8-9.

A young cowbird was observed in Fulton County, Georgia, on May 19, 1949, though no adults were present; this observation is only the second record of breeding cowbirds in Georgia.

Keywords: range expansion, Georgia

Parks, R. A. 1950. Cowbird breeding at Atlanta again. Oriole 15:32.

On May 27, 1950, the author observed a young cowbird near Atlanta, Georgia, approximately 100 yards from where a pair of hooded warblers raised a cowbird in 1949.

Keywords: range expansion, Georgia

Parks, R. A. 1958. Brown-headed cowbird breeding at Atlanta. Oriole 23:48-49.

A first-person account of a cowbird parasitizing a hooded warbler nest in DeKalb County, Georgia, in 1958.

Keywords: host species, Georgia

Parshall, S. E. 1884. The cowbird nuisance. Ornithol. and Oologist 9:138.

A first-person account of orioles being parasitized by the cowbird.

Keywords: host species

Payne, R. B. 1965. Clutch size and numbers of eggs laid by brown-headed cowbirds. Condor 67:44-60.

The author conducted this study to determine the clutch size and number of eggs laid by cowbirds during the breeding seasons of 1960 and 1963 in Michigan. Serial sections of the ovaries of 60 adult females were examined for post-ovulatory follicles. The numbers of eggs laid and the timing of laying were determined by comparing the size and histology of cowbird follicles to those of blackbirds of known breeding history. Results from this study reveal that female cowbirds are capable of laying an average of 10 to 12 eggs during the breeding season. The number of eggs laid by individual females varied, with some laying no eggs while others laying 15 at a minimum.

Keywords: fecundity, Michigan

Payne, R. B. 1967. Gonadal responses of brown-headed cowbirds to long day lengths. Condor 69:289-297.

The gonadal response of the brown-headed cowbird to long day lengths was compared with the photoperiodic responses of nonparasitic species in Berkeley, California, in 1964 and 1965. Also, the significance of the refractory period as a timing factor in the annual cycle of temperate-zone songbirds was evaluated by comparing the breeding seasons and timing of the refractory period of four species of North American icterids. Gonadal development in spring is not associated with a prolonged refractory period, but it is delayed until the completion of the partial prenuptial molt in late spring. The refractory periods of four species of North American icterids having different breeding seasons are terminated at the same time of year.

Keywords: physiology

Payne. R. B. 1973. The breeding season of a parasitic bird, the brown-headed cowbird, in central California. Condor 75:80-99.

To attempt to determine how the brown-headed cowbird adapted its breeding season to correspond with that of its potential hosts, which breed throughout the summer, the author observed cowbirds in central California from 1960-1965. It was noted that cowbirds continued nesting later into the summer than other icterids that occupied the same area, this late phase of their nesting coincides with the late nesting of some of their hosts. The breeding season of cowbirds appears to be a compromise between the increased fledging success associated with breeding throughout the season and parasitizing multiple hosts, and the reduction in the survival of migrating juveniles fledged later in the season, and the increased energy costs of such an extended breeding season.

Keywords: breeding season, California

Payne, R. B. 1976. The clutch size and numbers of eggs of brown-headed cowbirds: effects of latitude and breeding season. Condor 78:337-342.

A comparative study between populations of cowbirds from central California, southern Oklahoma, and northern Michigan showed a mean clutch size of 3.91 to 4.05 in all three areas. Estimates of the mean number of eggs laid in a season were 25.0 for Oklahoma, 24.1 for California, and 11.3 for northern Michigan. The smaller number of eggs laid by females in northern Michigan is due to the shorter breeding season of the local passerine hosts. No differences in clutch size were found that could be attributed to latitude, to total number of clutches laid in a season, or to the history of the populations.

Keywords: fecundity, California, Oklahoma, Michigan

Payne, R. B. 1977. The ecology of brood parasitism in birds. Ann. Rev. Ecol. Syst. 8:1-2

This report discusses host selection and specialization, effects of parasitism on breeding success of the host, behavior and evolutionary aspects of brood parasitism, breeding biology, social behavior, and population structure, and the evolution of brood parasitism in birds. The prevalence of single-egg nest parasitism suggests that brood parasitism may be an evolutionary Astrategy@ to reduce the risks of predation.

Keywords: brood parasitism, evolution

Peer, B. D. and E. K. Bollinger. 1997. Explanations for the infrequent cowbird parasitism on common grackles. Condor 99:151-161.

The authors determined the factors responsible for the lack of parasitism on grackles by cowbirds. No evidence of parasitism was found in 401 grackle nests that were monitored in east-central Illinois from 1992 to 1993. Nest abandonment by the grackles and mite infestation of grackle nests may decrease the suitability of grackles as hosts; however the primary reason for infrequent cowbird parasitism on grackles may be in their past ability to reject the cowbird eggs. Grackles likely rejected cowbird eggs at a higher frequency in the past and as a consequence grackles were avoided by cowbirds. The study results suggest that grackle rejection of cowbird eggs apparently decreased in the absence of parasitism due to the high degree of intraclutch egg variability exhibited by grackles which would increase the chances of them mistakenly rejecting their own discordant eggs.

Keywords: brood parasitism, host species, host defense

Phillips, R. S. 1951. Nest location, cowbird parasitism, and nesting success of the indigo bunting. Wilson Bull. 63:206-207.

During the summers of 1948, 1949, and 1950, the author observed 14 indigo bunting nests. Data on nest location, parasitism, and nesting success are tabulated. Six of the 14 nests were parasitized and only 1 cowbird was fledged from the 7 eggs laid. Of 41 bunting eggs laid, 18 young were fledged.

Keywords: host species, brood parasitism

Picman, J. 1986. Attempted nest parasitism of the marsh wren by a brown-headed cowbird. Condor 88:381-382.

The author describes the first recorded case of cowbird parasitism of the marsh wren in 1981 in British Columbia, Canada.

Keywords: brood parasitism, host species, British Columbia, Canada

Picman, J. 1989. Mechanism of increased puncture resistance of eggs of brown-headed cowbirds. Auk 106:577-583.

In this study, the author tests the resistance of brown-headed cowbird eggs to puncture, and compares the results to those of nonparasitic icterids. Cowbird eggs sustained nearly twice as much pressure during puncture resistance tests than eggs of three nonparasitic icterids. The greater strength of cowbird eggs is due primarily to thicker eggshells and a more rounded shape. The author also notes that the eggshells of cowbirds are comprised of a higher content of inorganic constituents than those of nonparasitic icterids.

Keywords: eggs

Picman, J. 1997. Are cowbird eggs unusually strong from the inside? Auk 114:66-73.

To evaluate the correlation of Aoutside@ eggshell strength on inside strength, the author measured the force required to puncture the inside of eggshells. Analyses among species demonstrated that the greater inside strength of cowbird eggs could be explained by their unusually thick eggshells. However, because cowbird eggshells were stronger than expected for their thickness, the author believes that other eggshell characteristics must also play a role in inside strength. These results suggest that hatching from cowbird eggs is more difficult than would be expected for eggs of their size.

Keywords: eggs

Pius, B. 1949. Indigo bunting nest with five cowbird eggs. Flicker 21:121.

This report is a first-person account of brood parasitism on the indigo bunting near St. Paul, Minnesota, in 1949. One cowbird egg was ejected, another hatched but did not survive to fledge.

Keywords: host species, Minnesota

Plank, W. 1919. Cowbird impositions. Oologist 36:18.

A series of first-person observations of parasitized nests of a phoebe, a mockingbird, a wood thrush, and a blue grosbeak.

Keywords: host species

Poiani, A. 1997. Noisy plasticity and evolution of brood parasitism. Hereditas 126:179-182.

The Nolan-Thompson hypothesis states that unpredictable fluctuations in main food sources for the ancestors of brood parasites may have resulted in a high annual variability in clutch size. In this note, the author argues that this hypothesis is both empirically and theoretically plausible and can be understood in the light of recent theoretical developments on the mechanisms of evolution of phenotypic plasticity.

Keywords: evolution

Poling, O. C. 1889. A list of birds in whose nests the cowbirds eggs have been found. Ornithol. and Oologist 14:133-134.

A list of first-person observations of cowbird parasitism of various species.

Keywords: host species

Poling, O. C. 1890. Further notes on the cowbird, with remarks on the nesting of the prothonotary warbler at Quincy, Illinois. Ornithol. and Oologist 15:92.

A first-person account of finding cowbird eggs in cavity nests.

Keywords: host species, Illinois

Post, W. and J. W. Wiley. 1977. The shiny cowbird in the West Indies. Condor 79:119-121. The authors describe an expansion in the range of the shiny cowbird into the Mediterranean. They anticipate that the cowbird will move rapidly through the remainder of the Greater Antilles, and predict that Cuba or Cozumel may serve as the final stepping-stone for the species invasion of North America.

Keywords: range expansion, Mediterranean, shiny cowbird

Post, W., T. K. Nakamura, and A. Cruz. 1990. Patterns of shiny cowbird parasitism in St. Lucia and southwestern Puerto Rico. Condor 92:461-469.

The authors compare parasite-host relationships in two areas of the Caribbean, where the shiny cowbird has been present for varying lengths of time. Patterns of parasitism did not match host availability in either southwestern Puerto Rico or St. Lucia. Comparisons with Puerto Rico indicate that neither hosts nor cowbirds in St. Lucia have evolved defenses or counter-defenses over a 40-year period.

Keywords: shiny cowbird, brood parasitism, host selection, host species, Puerto Rico

Post, W. 1992. First Florida specimens of the shiny cowbird. Florida Field Nat. 20:17-18.

A first-person account of the first collected specimen of the shiny cowbird in St. Lucie County, Florida, in July 25, 1991.

Keywords: shiny cowbird, range expansion, Florida

Post, W. and J. W. Wiley. 1992. The head-down display in shiny cowbirds and its relation to dominance behavior. Condor 94:999-1002.

This study reports the occurrence and frequency of the head-down display among free-living and captive shiny cowbirds; identifies the species to which the cowbirds displayed; the responses of the recipients; and the contexts in which the head-down occurred. The authors objective is to clarify the function of the head-down display in the shiny cowbird and to compare their data with similar information for the brown-headed cowbird. The study was conducted intermittently from 1973 to 1987 in Puerto Rico.

Keywords: shiny cowbird, behavior, Puerto Rico

Post, W. and A. Cruz. 1993. The North American invasion pattern of the shiny cowbird. J. Field Ornithol. 64:32-41.

Long-range movements of shiny cowbirds in North America support the hypothesis that the cowbird spread from South America, and was not introduced by humans. The authors discuss the pattern of range expansion of the shiny cowbird in North America.

Keywords: shiny cowbird, range expansion

Porter, D. K. 1973. First observation of cowbird parasitism on lark buntings in Colorado. C.F.O. Journal 16:18.

Keywords: host species, Colorado

Posson, N. F. 1890. More cowbird eggs. Ornithol. and Oologist 15:31.

A first-person account of the first recorded cowbird parasitism of the kingbird and meadowlark.

Keywords: host species

Potter, L. B. 1939. Shrikes, red-wings, and the cowbird. Condor 41:219-220.

A first-person account of cowbird parasitism of white-rumped shrikes and red-winged blackbirds in Saskatchewan, Canada, in 1938.

Keywords: host species, Saskatchewan, Canada

Potvin, N., J. M. Bergeron, M. Norman, and A. Cyr. 1982. Evaluating the sterile male method on red-winged blackbirds: effects of the chemosterilant thiotepa on the reproduction of clinically treated birds under field conditions. Can. J. Zool. 60:2337-2343.

In the spring of 1978 and 1979, flocks of blackbird composed of red-winged blackbirds, grackles, and cowbirds reached a maximum of 5,000 birds in the study area in Quebec, Canada. Chemosterilization was applied to the flock over a 1-month period. Three sets of experiments were conducted to determine the feasibility and effectiveness of the chemosterilization method in reducing blackbird populations. Results from these experiments indicate that this sterilization approach, conducted under field conditions, can be an effective means of reducing blackbird populations causing crop damage.

Keywords: population control, Quebec, Canada

Prescott, K. W. 1947. Unusual behavior of a cowbird and scarlet tanager at a red-eyed vireo nest. Wilson Bull. 59:210.

In this paper the observations of a cowbird parasitizing a red-eyed vireo nest and being attacked by a scarlet tanager are presented.

Keywords: behavior, host species

Pribil, S. and J. Picman. 1997. Parasitism of house wren nests by brown-headed cowbirds: why is it so rare? Can. J. Zool. 75:302-307.

The authors tested five hypotheses in an attempt to explain why wren nests are rarely parasitized by brown-headed cowbirds. These hypothesis include: the inaccessible-entrance hypothesis; the nest-structure hypothesis; the puncture-ejection hypothesis; the egg-burial hypothesis; and the nest-desertion hypothesis. Results from this study were consistent with the inaccessible-entrance hypothesis. The authors also suggest that additional nesting adaptations, as well as active cowbird avoidance of house wrens, may contribute to the low frequency of cowbird parasitism.

Keywords: host defense, host species

Price, H. F. 1934. A few cowbird notes. Oologist 51:107-108.

Keywords: host species

Ratcliffe, L. and R. Weisman. 1987. Phrase order recognition by brown-headed cowbirds. Anim. Behav. 35:1260-1262.

The authors suggest that the role of syntax in song recognition may be underestimated, and use the song of the cowbird as an example. The authors tested whether phrase context or syntax was critical to species song recognition by female cowbirds. The results confirm the results of previous studies that the first and second components of male song are critical to eliciting female response.

Keywords: behavior, vocalization

Regosin. J. V. 1994. Scissor-tailed flycatchers eject brown-headed cowbird eggs. J. Field Ornithol. 65:508-511.

In 1991 and 1992, the nesting biology of the scissor-tailed flycatcher was studied by monitoring 180 active nests, of which three were parasitized by cowbirds. Of the three naturally parasitized nests, the cowbird eggs were ejected from two of the nests, and the other was destroyed in a storm. All eggs were ejected from three experimental nests which had been artificially parasitized by the authors.

Keywords: brood parasitism, host defense, egg manipulation

Robertson, L. 1997. 1996 cowbird control program. Prepared for U.S. Bureau of Reclamation, Albuquerque Area Office.

The U.S. Bureau of Reclamation undertook a brown-headed cowbird trapping program in 1996 near San Marcial, New Mexico, in an effort to reduce brood parasitism on the southwestern willow flycatcher. Over the course of the trapping effort, 1,140 cowbirds were collected and euthanized. Since only one unsuccessful flycatcher nesting attempt was recorded in the San Marcial area in 1996, the effectiveness of removing cowbirds from the local population in an attempt to reduce parasitism of the endangered flycatcher could not be determined.

Keywords: population control, trapping

Robertson, R. J. and R. F. Norman. 1976. Behavioral defenses to brood parasitism by potential hosts of the brown-headed cowbird. Condor 78:166-173.

Field experiments to determine behavioral defenses of cowbird hosts were conducted from 1972-1974 near Kingston, Ontario, Canada. The authors investigated host responses to cowbirds by placing models of cowbirds and other species in close proximity to the active nests of 15 potential host species. The behavioral responses of all host were recorded. Data supported the hypothesis that potential cowbird hosts demonstrate behavioral defenses of an intensity directly proportional to the degree of which they are parasitized.

Keywords: host defense, host species, Ontario, Canada

Robertson, R. J. and R. F. Norman. 1977. The function and evolution of aggressive host behavior towards the brown-headed cowbird (Molothrus ater). Can. J. Zool. 55:508-518.

Aggression to model cowbirds was observed and recorded at 34 nests of potential host species. The intensity of aggression towards the model cowbird was positively correlated with the rate of parasitism experienced by the individual host species These data were used to test two hypotheses: that aggression functions as an anti-parasite defense reducing parasitism; and that cowbirds use host aggression as a cue when searching for nests. The results further suggest that host aggression only serves as an effective anti-parasite defense in dense host populations.

Keywords: host defense, host species

Robinson, S. K., S. I. Rothstein, M. C. Brittingham, L. J. Petit, and J. A. Grzybowski. 1995. Ecology and behavior of cowbirds and their impact on host populations. Pages 428-460 in T. E. Martin and D. M. Finch (eds.). Ecology and management of neotropical migratory birds: a synthesis and review of critical issues. Oxford University Press, New York, New York, USA.

Keywords: behavior

Robinson, S. K., J. A. Grzybowski, S. I. Rothstein, M. C. Brittingham, L. J. Petit, and F. R. Thompson 1993. Management implications of cowbird parasitism on neotropical migrant songbirds. Pages 93-102 in D. M. Finch and P. W. Stangel (ed.). Status and management of neotropical migratory birds. USDA Forest Service General Technical Report RM-229.

The authors of this report recommend the development of broader-scale approaches, perhaps in combination with local trapping as a means of reducing brood parasitism. They suggest consolidation of ownership to preserve large tracts, eliminating potential cowbird feeding areas within large tracts, and minimizing edge habitat as a means of controlling cowbird numbers on a landscape level. Another means of controlling cowbirds is through large-scale eradication at winter roosts, however eradication on winter roost would likely be too diffuse to reduce parasitism at the local level where sensitive species are of significant concern.

Keywords: population control

Robinson, S. K. 1988. Foraging ecology and host relationships of giant cowbirds in southeastern Peru. Wilson Bull. 100:224-235.

The author studied the foraging ecology and host species relations of a population of giant cowbirds in Manu National Park of Amazonian Peru. The cowbirds regularly visited colonies of two potential host species, the yellow-rumped cacique and the russet-backed oropendola, but were known to parasitize only the oropendola.

Keywords: giant cowbirds, host-parasite relationships, host species, Peru

Rogers, C. M., M. J. Taitt, J.N.M. Smith, and G. Jongejan. 1997. Nest predation and cowbird parasitism create a demographic sink in wetland-breeding song sparrows. Condor 99:622-633.

The authors studied the poor breeding performance in a color-banded population of song sparrows in coastal British Columbia from 1988 to 1991, and attempted to identify the underlying causes. Predation was the leading cause of nest failure (42% of nests), followed by abandonment as a result of cowbird parasitism (34%). The study site was determined to be a population sink for song sparrows due to the high rates of nest predation and brood parasitism. These factors may be contributing to the significant long-term decline of the song sparrow in British Columbia and throughout Canada.

Keywords: brood parasitism, host species, British Columbia, Canada

Rohwer, S. and C. D. Spaw. 1988. Evolutionary lag versus bill-size constraints: a comparative study of the acceptance of cowbird eggs by old hosts. Evol. Ecol. 2:27-36.

This study was conducted to show that most acceptors of brown-headed cowbird eggs have small bills; that the single species known to puncture cowbird eggs for ejection also has a small bill; and that all grasp ejectors of cowbird eggs have large bills. The authors propose that most cowbird egg acceptors are incapable of removing the eggs due to their small bill size. They also propose that smaller host species probably do not puncture cowbird eggs for ejection because the cowbirds unusually thick shells make the costs of puncturing them higher than the benefits of ejection.

Keywords: evolution, host defense

Romig, G. P. and R. D. Crawford. 1995. Clay-colored sparrows in North Dakota parasitized by brown-headed cowbirds. Prairie Nat. 27:193-203.

The impact of cowbird parasitism on the reproductive success of a clay-colored sparrow population located at Oakville Prairie, Grand Forks County, North Dakota, was studied from early May to late July 1992. Sixteen of 42 sparrow nests were parasitized by cowbirds. Of the 16 parasitized nests, 3 were abandoned by the sparrows, and apparently no cowbird eggs were ejected. Based on these results, the clay-colored sparrows were considered to be cowbird egg acceptors and tolerant hosts.

Keywords: brood parasitism, host species, North Dakota

Root, O. M. 1942. Myrtle warbler feeding a young cowbird. Wilson Bull. 54:253.

This article is a first-person account of a warbler feeding a fledgling cowbird in Michigan in 1942.

Keywords: host species, Michigan

Roskaft, E., S. Rohwer, and C. D. Spaw 1993. Cost of puncture ejection compared with costs of rearing cowbird chicks for northern orioles. Ornis Scand. 24:28-32.

The authors experimentally added natural brown-headed cowbird eggs to the nests of northern orioles. The cowbird eggs are known to have a substantially stronger shell than those of comparable-sized passerines. The hatching success of damaged oriole eggs was less than 45%, while 99% of the undamaged eggs hatched. These results allowed the authors to estimate that the cost of puncture-ejecting cowbird eggs results in the loss of 0.26 oriole eggs for each cowbird egg ejected. The authors also determined the cost of rearing a cowbird chick by placing a newly hatched cowbird chick in the orioles nest shortly after the oriole eggs hatched. Results indicate that the cost of rearing a cowbird chick exceeds the cost of puncture ejection when four oriole chicks are present in the nest.

Keywords: host defense, host species

Rothstein, S. I. 1970. An experimental investigation of the defenses of the hosts of the parasitic brown-headed cowbird (Molothrus ater). Ph.D. diss. Yale University, New Haven.

Keywords: host defense

Rothstein, S. I. 1971. Observation and experiment in the analysis of interactions between brood parasites and their hosts. Amer. Nat. 105:71-74.

The author submits a letter to the editor, providing additional information to a paper on brood parasitism, that particularly points on the polymorphism of egg color.

Keywords: brood parasitism

Rothstein, S. I. 1971. A reanalysis of the interspecific invitation to preening display as performed by the brown-headed cowbird (Molothrus ater). Amer. Zool. 11:638.

The author discusses observations of captive cowbirds performing the preening display. His findings suggest that the preening display is an aggressive behavior that functions intra- and interspecifically. Cowbirds apparently use this display to dominate other birds and to integrate social units.

Keywords: behavior

Rothstein, S. I. 1972. Territoriality and mating system in the parasitic brown-headed cowbird (Molothrus ater) as determined from captive birds. Amer. Zool. 12:659.

Observations indicate that cowbirds are territorial in the morning and agree with information obtained from nature. Observations also indicate that, despite their parasitism, cowbirds are monogamous. Abstract only.

Keywords: mating system, territorial behavior

Rothstein, S. I. 1974. Mechanisms of avian egg recognition: possible learned and innate factors. Auk 91:796-807.

The experiments reported in this study were conducted on naturally breeding gray catbirds. The author provides an analyses of the experiments that involve egg recognition early in the breeding cycle, and identifies which components of rejection are learned and which are innate. Egg recognition by learning has significant implications as it affects the long-term evolutionary behavior between brood parasites and their hosts. The author suggests that hosts which learn their own egg type are capable of evolving additional anti-parasite adaptations easier than hosts that innately recognize their own eggs.

Keywords: brood parasitism, host defense

Rothstein, S. I. 1975. An experimental and teleonomic investigation of avian brood parasitism. Condor 77:250-271.

In this study the author conducts the first systematic attempt to investigate experimentally the presence or absence of anti-parasite adaptations in a large number of actual and potential host species of a parasitic bird. Experiments were conducted by artificially parasitizing 640 nests of 43 species of potential cowbird hosts by placing a cowbird egg in their nests. Of the species with sufficient data, 23 were considered acceptors and seven were considered rejectors. The results of this study indicate that most North American birds lack sufficient host defenses, and support the belief that the host-parasite relationship is not highly evolved.

Keywords: brood parasitism, evolution, egg manipulation

Rothstein, S. I. 1975. Evolutionary rates and host defenses against avian brood parasitism. Amer. Nat. 109:161-176.

In this study the author attempts to determine why there is uniformity within species in the expression of host defenses. The author presents a hypothesis relating the low variation in expression of host defenses to the rate at which the incidence of a hosts defense increases over evolutionary time. Field data applied to a model capable of deriving the selection coefficient for a hosts defense against parasitism is used to support the hypothesis. Keywords: host defense, model

Rothstein, S. I. 1975. Mechanisms of avian egg recognition: do birds know their own eggs? Anim. Behav. 23:268-278.

The results from a multiple experiments reveal that rejector-species do indeed recognize their own eggs. If rejector-species show intolerance toward any type of egg, they reject the foreign eggs whether these are as numerous as their own eggs, outnumber their own eggs, or are the only egg-type present. These and other results are analyzed in the context of the evolutionary pressures exerted on birds by brood parasites.

Keywords: eggs, host defense

Rothstein, S. I. 1976. Cowbird parasitism of the cedar waxwing and its evolutionary implications. Auk 93:498-509.

The author presents data showing that cowbird parasitism is indeed a selective pressure on the cedar waxwing and that these data are necessary to develop a meaningful interpretation of the responses to experimental parasitism since host behavior evolved as a natural defense to brood parasitism. This article discusses the frequency of parasitism and the probable degree of reproductive loss caused by the parasitism. The author also discusses the implications that parasitism of the waxwing has for considerations of the Astrategies@ cowbirds may use in selecting their hosts.

Keywords: brood parasitism, host species

Rothstein, S. I. 1976. Experiments on defenses cedar waxwings use against cowbird parasitism. Auk 93:675-691.

In this study the author presents a detailed analysis of experiments conducted on the cedar waxwing. He also contrasts the waxwings defenses with the simpler ones of other rejector species and suggests reasons for the differences.

Keywords: host defense, host species

Rothstein, S. I. 1977. Cowbird parasitism and egg recognition of the northern oriole. Wilson Bull. 89:21-32.

Experiments on 28 northern oriole nests indicate that this species does not tolerate cowbird parasitism. Artificial cowbird eggs, authentic cowbird eggs, and authentic house sparrow eggs, which resemble cowbird eggs, were rejected at all oriole nests. The orioles immediate rejection of the eggs indicates that the degree of parasitism that is actually observed is only a fraction of the total parasitism that occurs.

Keywords: host defense, host species, egg manipulation

Rothstein, S. I. 1977. The preening invitation or head-down display of parasitic cowbirds: I. Evidence for intraspecific occurrence. Condor 79:13-23.

In this report, data are presented showing the high frequency of intraspecific displays. The author also shows that intraspecific displays follow strong, repeatable patterns when the identities of displayers and display recipients are analyzed.

Keywords: behavior

Rothstein, S. I. 1978. Geographical variation in the nestling coloration of parasitic cowbirds. Auk 95:152-160.

Twenty-four cowbirds from the Southwest, where the race Molothrus ater obscurus breeds, had yellow flanges whereas 73 from the remainder of the United States and Canada, where the races artemisiae and ater breed, had white flanges. There is little or no intralocality variation. Nestling cowbirds with yellow and white flanges apparently are accepted and fed by hosts regardless of the color of the rictal flanges of the hostss own young, but the author hypothesizes that the quality of host care received by a nestling cowbird is influenced by its rictal flange color and that host responses are the selective pressure responsible for the geographical variation.

Keywords: subspecific variation

Rothstein, S. I. 1978. Mechanisms of avian-egg recognition: additional evidence for learned components. Anim. Behav. 26:671-677.

In this paper, the author examines the ontogeny of rejection-behavior in San Luis Obispo County, California, in 1974 and 1975. In addition to experiments on the ontogeny of the northern orioles egg-recognition, the author presents data on another aspect of learning: habituation. The author addresses the question of whether orioles learn to stop responding to a cowbird egg if the egg remains in the nest. He also reports on experiments that test the orioles reaction to foreign eggs whose appearance is distinct from cowbird eggs.

Keywords: host defense, host species

Rothstein, S. I. 1980. The preening invitation or head-down display of parasitic cowbirds: II. Experimental analysis and evidence for behavioral mimicry. Behaviour 75:148-184.

In this study the author examines the behavioral responses of cowbirds through a series of four experiments. In the first experiment, cowbirds which were resident to their cages, directed significantly more displays to male and female cowbirds and female red-winged blackbirds that were introduced into the cages than the residents did to each other. However, introduced female red-wings elicited more displays than introduced cowbirds. The second experiment indicated that redwings are stronger releasers than cowbirds due to their submissive and fearful behavior. The results of experiment 3 support the hypothesis that aggression plays a major role in this display, and experiment 4 supported the results of experiment 3.

Keywords: behavior

Rothstein, S. I., J. Verner, and E. Stevens. 1980. Range expansion and diurnal changes in dispersion of the brown-headed cowbird in the Sierra Nevada. Auk 97:253-267.

An extensive literature search and survey of specimens from scientific collections in California indicated that prior to 1930, cowbirds were virtually absent from the entire Sierra Nevada range of California. The current distribution, diurnal patterns of dispersal, seasonal occurrence, and host species were studied from 1975 to 1978. The authors did not determine whether cowbirds were present in remote areas void of human development, therefore it is possible that large, isolated stands of mature forest may remain free of cowbird parasitism.

Keywords: behavior, distribution, host species, movements, California

Rothstein, S. I. 1982. Mechanisms of avian egg recognition: which egg parameters elicit responses by rejector species? Behav. Ecol. Sociobiol. 11:229-239.

Experiments presented in this report examine the specific egg parameters to which rejector species respond; the relative tolerances rejectors show towards nonmimetic eggs; and the degree to which rejection is limited to eggs of the brown-headed cowbird. Rejector species exhibit degrees of tolerance proportional to the physical divergence between their eggs and those of the cowbird. Host species which lay eggs similar to those of the cowbird must be relatively intolerant to maximize the chances that cowbird eggs are rejected. The experiments conducted in this study indicate that rejection is not specific to cowbird eggs. Therefore, it is apparent that host species have developed an evolutionary response to brood parasitism by developing the ability to recognize their own eggs, rather than by developing recognition and rejection specific to parasitic eggs.

Keywords: eggs, host defense

Rothstein, S. I. 1982. Successes and failures in avian egg and nestling recognition with comments on the utility of optimality reasoning. Amer. Zool. 22:547-560.

The author conducted a series of egg and nestling recognition studies in San Luis Obispo County, California, from 1974 to 1976. Although these recognition studies demonstrate the value of optimality reasoning, they also demonstrate some general problems inherent in optimization models. The author cautions readers, that while optimality reasoning is the best and most all-inclusive paradigm in biology, its value will be enhanced if its limitations are recognized.

Keywords: brood parasitism, California

Rothstein, S. I., J. Verner, and E. Stevens. 1984. Radio-tracking confirms a unique diurnal pattern of spatial occurrence in the parasitic brown-headed cowbird. Ecology 65:77-88. With the use of radio telemetry, the author was able to document that five females and four of eight males spent their mornings in host-rich habitats and then commuted 2.1 to 6.7 km to one or more feeding sites and remained there for the rest of the day. Four noncommuting males, which were all yearlings and possibly socially subordinate, also showed high mobility but did not occupy the same area each morning. The authors found little evidence of territoriality on morning ranges, nor evidence of prolonged pair bonds.

Keywords: behavior, movements, radio telemetry

Rothstein, S. I., D. A. Yokel, and R. C. Fleisher. 1986. Social dominance, mating and spacing systems, female fecundity, and vocal dialects in captive and free-ranging brown-headed cowbirds. Curr. Ornithol. 3:127-185.

This report presents the findings of captive cowbird behavioral, and discusses advantages and limitations of such studies. When cowbirds from the same populations are used in captive and field studies, the results are generally comparable. This report also focuses on the breeding biology of the cowbird, which varies little over its vast range. The authors contend that regardless of the wide range of habitats that the cowbird occupies, females exhibit a similarly high rate of egg laying.

Keywords: fecundity, mating system, social organization, vocalization

Rothstein, S. I., J. Verner, E. Stevens, and L. V. Ritter. 1987. Behavioral differences among sex and age classes of the brown-headed cowbird and their relation to the efficacy of a control program. Wilson Bull. 99:322-337.

A cowbird control program was tested by removing 125 cowbirds from a pack station in the western Sierra Nevada. Although total cowbird numbers in the immediate vicinity of the removal site declined markedly, there was only a moderate decline in male cowbirds, and at best only a slight decline in female cowbirds in the general area surrounding the removal site. The removal program had limited impact since many cowbirds in the area, especially females and adult males, often foraged in association with cattle grazing in meadows.

Keywords: population control

Rothstein, S. I. and R. C. Fleischer. 1987. Vocal dialects and their possible relation to honest status signaling in the brown-headed cowbird. Condor 89:1-23.

The authors describe cowbird flight whistle dialects and contrast previous hypotheses for the maintenance of dialects with a new one that assumes that a males ability to give the correct local dialect represents relatively high male quality. The three dialects upon which they focused are part of an extensive dialect system along the eastern Sierra Nevada. These data are consistent with the honest convergence hypothesis and inconsistent with the hypotheses that dialects are maintained by isolation or because they contribute to local adaptation among populations.

Keywords: vocalization

Rothstein, S. I. and R. C. Fleischer. 1987. Brown-headed cowbirds learn flight whistles after the juvenile period. Auk 104:512-516.

The authors report on the variations in flight whistles developed by captive cowbirds exposed to live, rather than taped, tutors.

Keywords: vocalization

Rothstein, S. I. et al. 1988. The agonistic and sexual functions of vocalizations of male brown-headed cowbirds, Molothrus ater. Anim. Behav. 36:73-86.

Functional analyses of three vocalizations of male cowbirds, two of which are songs, are presented in this report. The different results for western and eastern birds may be a result of captivity and/or a result of geographical variation in behavior.

Keywords: vocalization

Rothstein, S. I. 1990. A model system for coevolution: avian brood parasitism. Annu. Rev. Ecol. Syst. 21:481-508.

The author provides a summary of obligate brood parasitism within the seven avian taxa that contain parasites, and describes how it has affected natural coevolution.

Keywords: brood parasitism

Rothstein, S. I. 1990. Brood parasitism and clutch-size determination in birds. Trends in Ecol. and Evolution 5:101-102.

This study focuses on clutch size as it applies to conspecific brood parasitism.

Keywords: brood parasitism

Rothstein, S. I. 1993. An experimental test of the Hamilton-Orians hypothesis for the origin of avian brood parasitism. Condor 95:1000-1005.

Red-winged blackbird nests were removed after females laid their first eggs and other nests in the same colonies were monitored to determine whether the affected blackbird females laid subsequent eggs parasitically. No parasitic eggs appeared in the monitored nests; however, in some cases, fresh eggs were found the next day at the sites of removed nests. The authors determine that the initial response in the Hamilton-Orians hypothesis is uncommon or absent in red-winged blackbirds. A literature review and recent data indicate that blackbirds lack brood parasitism defenses, therefore the failure to elicit parasitism experimentally of this species is enigmatic.

Keywords: brood parasitism

Rothstein, S. I. 1994. The cowbirds invasion of the far west: history, causes and consequences experienced by host species. Stud. Avian Biol. 15:301-315.

The author presents an overview of the history and events leading to the cowbirds expansion into the Far West. He also discusses the consequences experienced by some host taxa that were once abundant but are now declining.

Keywords: host species, range expansion

Rothstein, S. I. and S. K. Robinson. 1994. Conservation and coevolutionary implications of brood parasitism by cowbirds. Trends in Ecol. and Evolution 9:162-164.

A summary of The Ecology and Management of Cowbirds Conference held in Austin, Texas, in November 1993.

Keywords: population control, Texas

Rothstein, S.I., J. Verner and C. Farmer. In press. Cowbird vocalizations: an overview and the use of playback to enhance cowbird detectability. In J.N.M. Smith, T.L. Cook, S.K. Robinson, S.I. Rothstein and S.G. Sealy (eds.). Ecology and management of cowbirds and their hosts. University of Texas Press, Austin, Texas.

The authors describe the structure, function, and ontogeny of five distinct cowbird songs, and calls. The female chatter call was used in a tape-playback field experiment in the Sierra Nevada of California to determine whether the use of this call would increase the detectability of both male and female cowbirds during standard 10-minute point counts. The authors detected twice as many males, and four times as many females using the female chatter call tape-playback as they did while conducting the point counts without the use of the tape-playback.

Keywords: vocalization

Rowley, J. S. 1930. Observations on the dwarf cowbird. Condor 32:130-131.

The author notes the apparent increase in cowbird numbers from 1920 to 1929 in southern California, and includes a list of host species and the number of eggs observed in the nests of some host species.

Keywords: host species, range expansion, California

Saldanha, C. J. and B. A. Schlinger. 1997. Estrogen synthesis and secretion in the brown-headed cowbird (Molothrus ater). General and Comparative Endocrinology 105:390-401.

In this study the authors examined the patterns of estrogen synthesis in various tissues of the cowbird. The gonadal tissue from adult male and female cowbirds was injected in vivo or provided in vitro to telencephalic with radiolabeled aromatizable androgenic substrate. Telencephalic aromatase may be characteristic of passerine songbirds and may function to provide local estrogenic cues to estrogen-sensitive neural loci, and/or contribute to peripheral estrogen titers in male and female songbirds.

Keywords: endocrinology

Salmon, W. L. 1933. Song sparrow and cowbirds. Bird-Lore 35:100.

A first-person account of a song sparrow feeding three fledgling cowbirds in California in 1932 is presented in this article.

Keywords: host species, California

Salvador, S. A. 1983. Brood parasitism by shiny cowbirds (Molothrus bonariensis) in Villa Maria, Cordoba, Argentina. Historia Natural 3:149-158.

In this study, shiny cowbirds were found to parasitize 31.4% of the local passerine species, and were larger and heavier than in Buenos Aires. In Spanish, abstract in English.

Keywords: shiny cowbird, brood parasitism, Argentina

Savage, D. L. 1897. Observations on the cowbird. Iowa Ornithol. 3:4-7.

The author briefly discusses the parasitic habits and natural history of the cowbird, citing records of unusual observations.

Keywords: brood parasitism, life history

Schweitzer, S. H., D. M. Finch, D. M. Leslie, Jr. 1996. Reducing impacts of brood parasitism by brown-headed cowbirds on riparian-nesting migratory songbirds. Pages 267-276 in D. W. Shaw and D. M. Finch (tech coords.). Desired future conditions for southwestern riparian ecosystems: bring interest and concern together. USDA Forest Service General Technical Report RM 272.

Keywords: population control

Scott, D. M. 1963. Changes in the reproductive activity of the brown-headed cowbird within the breeding season. Wilson Bull. 75:123-129.

In this report the author addresses the changes in the reproductive activity of the cowbird. Data are gathered by reviewing cowbird parasitism on the cardinal, by examining the reproductive organs of adult cowbirds, and by observing post-nuptial flocks of adult cowbirds. The breeding season of the cowbird extends from late April to late July, however the maximum reproductive activity of female cowbirds is maintained over an 8-week period in May and June. Parasitism on the cardinal is discussed relative to changes in the laying activity of the cowbird.

Keywords: brood parasitism, host species

Scott, D. M. and A. L. A. Middleton. 1968. The annual testicular cycle of the brown-headed cowbird (Molothrus ater). Can. J. Zool. 46:77-87.

An analysis of the spermatogenic condition and testes weights from 450 cowbirds was made to determine the annual cycle of this species at London, Ontario, and to ascertain variation in the cycle due to age. Testes, apparently undergoing regression, were noted more frequently in adults than in yearlings in May and early June at the height of the breeding season. The significance of this observation and some aspects of testicular regression are discussed. During the breeding season, adult males are more sedentary and habitually associate with the same female more than most yearlings. These behavioral differences may be related to the observed differences between the age groups in the testicular cycle.

Keywords: endocrinology, physiology, Ontario, Canada

Scott, D. M. 1977. Cowbird parasitism on the gray catbird at London, Ontario. Auk 94:18-27.

Parasitism by the brown-headed cowbird on the gray catbird, the red-eyed vireo, the yellow warbler, the cardinal, and the song sparrow was studied at London, Ontario, in 1969. This study was conducted to test the hypothesis that parasitism rates between catbirds and other host species were similar. The incidence of observed parasitism on 16 catbird nests was 44%, and 85% on 27 nests of the other hosts. The frequency distribution of the numbers of cowbird eggs per parasitized catbird nest was significantly different from that on the other hosts. The author concludes that the actual amount of parasitism was probably less for catbirds than for the other hosts.

Keywords: host defense, host species, Ontario, Canada

Scott, D. M. 1978. Using sizes of follicles to estimate the laying rate of the brown-headed cowbird. Can. J. Zool. 56:2230-2234.

The author found the average daily egg laying rate of the cowbird equals the clutch size divided by the sum of the clutch size and the interval. Based on a heterogeneous sample, the laying rate is about 0.66 eggs.

Keywords: laying rate

Scott, D. M. and C. D. Ankney. 1979. Evaluation of a method for estimating the laying rate of brown-headed cowbirds. Auk 96:483-488.

In this study the authors collected and examined 400 female cowbirds from southern Ontario during the breeding seasons of 1976 and 1977 in an effort to determine the laying rate of cowbirds. The proportion of females containing an egg in the oviduct was independent of six variables: habitat, year, time of day, method of detection in breeding and feeding habitats, sociality, and method of collecting. Authors conclude that the proportion of collected females with an oviducal egg can be a good estimate of the average daily laying rate. This was about 0.8 eggs per female in late May and early June.

Keywords: fecundity, laying rate, Ontario, Canada

Scott, D. M. and C. D. Ankney. 1980. Fecundity of the brown-headed cowbird in southern Ontario. Auk 97:677-683.

The authors collected 850 female cowbirds in southern Ontario over a period of six breeding seasons to determine the average number of eggs laid annually by a cowbird. They estimated this number by multiplying the length of an average laying season by the average daily laying rate. Using this formula, the authors estimated that an average female cowbird lays approximately 40 eggs during the breeding season. Furthermore, assuming she breeds for two seasons, her lifetime fecundity is about 80 eggs. This estimate is consistent with estimates of cowbird survival: 0.15 from egg to fledgling, 0.50 from fledging to independence, and 0.40 from independence to adulthood.

Keywords: fecundity, Ontario, Canada

Scott, D. M. and C. D. Ankney. 1983. The laying cycle of brown-headed cowbirds: passerine chickens? Auk 100:583-592.

The authors collected 270 female cowbirds in southern Ontario in 1976 to determine ovarian and oviducal growth during the breeding season and 188 female cowbirds in 1977 to estimate clutch size and the interval between clutches. Results of the study indicate that the average clutch size was about 4.0 to 4.6 eggs, similar to clutch sizes of nonparasitic icterids. Two days without laying usually separated consecutive clutches, however some females missed laying only a single day between clutches. The extended reproductive period without regression and the short interval between clutches exhibited by the cowbird are atypical of passerine reproduction. The author compares the laying cycle of cowbirds to that of domestic chickens.

Keywords: laying rate, Ontario, Canada

Scott, D. M. 1988. House sparrow and chipping sparrow feed the same fledgling brown-headed cowbird. Wilson Bull. 100:323-324.

This paper consists of a first-person account of two species successively feeding the same cowbird fledgling in London, Ontario, in 1986.

Keywords: host species, Ontario, Canada

Scott, D. M. 1991. The time of day of egg laying by the brown-headed cowbird and other icterines. Can. J. Zool. 69:2093-2099.

The author presents data on the time of day of oviposition for 16 species of icterines to evaluate the idea that laying early in the morning by the cowbird is a specialized adaptation for parasitism. Although the female cowbird in this region lays her eggs earlier than most local passerines, these data are inadequate to conclude that early laying by cowbirds has evolved as an adaptation for parasitism.

Keywords: brood parasitism, laying rate

Scott, D. M., P. J. Weatherhead, and C. D. Ankney. 1992. Egg-eating by female brown-headed cowbirds. Condor 94:579-584.

The authors estimated the proportions of eggs and nestlings, removed from hosts nests, that were eaten by female cowbirds by reviewing a compilation of published and unpublished observations, and by the proportion of removed eggs that were found uneaten below parasitized cardinal nests. Although egg-eating provides nutrient value, approximately 40% of removed eggs were not eaten by the cowbird. The authors offer six explanations to account for the failure of cowbirds to eat many eggs, and suggest experiments to study this behavior. The authors conclude that eggs for food consumption may not be the primary cause of egg removal by cowbirds.

Keywords: brood parasitism, host species, eggs, predation

Scott, D. M. and R. E. Lemon. 1996. Differential reproductive success of brown-headed cowbirds with northern cardinals and three other hosts. Condor 98:259-271.

In this study the authors compared the cowbird fledging success of the song sparrow, chipping sparrow, and yellow warbler, to that of the cardinal, in an attempt to develop a better understanding of why larger cowbird hosts fail to successfully fledge as many cowbird young as do smaller hosts. Cardinals had the lowest number of successful broods per host-pair. The authors suggest that host brood-reduction enables cowbirds to exploit large hosts, particularly when the host-incubation period is short.

Keywords: brood parasitism, host species

Scott, T. W. 1977. Agonistic behavior and social organization of the brown-headed cowbird (Molothrus ater). M.S. thesis. Bowling Green State University, Bowling Green.

Keywords: social organization, behavior, Ohio

Scott, T. W. 1979. Growth and age determination of nestling brown-headed cowbirds. Wilson Bull. 91:464-466.

The objectives of this study were to develop a better understanding of the growth and development of cowbird nestlings. The body weight and linear measurements were recorded on cowbird nestlings in northwestern Ohio in 1975. Twenty-three cowbird eggs were located in 17 nests. Nine eggs hatched, five nestlings fledged; three at 10 days of age and two at 11 days. The authors suggest that researchers attempting to age large numbers of nestling cowbirds should consider total body length as the single best means for age determination. The authors also state that body length must be measured during days 1 and 2 to accurately determine a nestlings age.

Keywords: morphology, Ohio

Scott, T. W. and J. M. Grumstrup-Scott. 1983. Why do brown-headed cowbirds perform the head-down display? Auk 100:139-148.

Four hypotheses for the function of the head-down display were tested by observing free-ranging and captive cowbirds. While roosting in mixed-species flocks adjacent to feeding areas, free-ranging cowbirds performed 284 interspecific and 4 intraspecific displays over 59.2 daylight hours. The following hypothesis was proposed by the authors to explain the displays function: the head-down display of cowbirds is an appeasing agonistic behavior, the displayor is most often dominant to the recipient, and subsequent displaying is stimulated by interspecific preening. The authors further suggest that the head-down display may also function as a means of obtaining food, minimizing roost energetics, and/or establishing flock order.

Keywords: behavior, social organization

Sealy, S. G. 1992. Removal of yellow warbler eggs in association with cowbird parasitism. Condor 94:40-54.

In this study, the author quantified the removal of host eggs by the brown-headed cowbird from parasitized yellow warbler nests in Manitoba, Canada. Female cowbirds removed one warbler egg from approximately one out of every three parasitized nests. Explanations for the removal of eggs at the time of parasitism are summarized and two hypotheses are tested. The results suggest that cowbirds can remove at least two eggs without risking desertion by the warblers.

Keywords: brood parasitism, host species, Manitoba, Canada

Sealy, S. G. 1995. Burial of cowbird eggs by parasitized yellow warblers: an empirical and experimental study. Anim. Behav. 49:877-889.

The behavioral responses of yellow warblers to naturally laid and experimentally introduced cowbird eggs were recorded. The author suggests that the dichotomy of responses exhibited by warblers to cowbird parasitism may be due to the high cost of rejection. The strategy employed by warblers whether to reject or accept cowbird eggs may change over time as the costs and benefits of such strategies vary with environmental conditions.

Keywords: host defense, host species

Sealy, S. G., D. L. Neudorf, and D. P. Hill. 1995. Rapid laying by brown-headed cowbirds Molothrus ater and other parasitic birds. Ibis 137:76-84.

In order to evaluate the hypothesis that rapid laying by parasitic cowbirds and other parasitic birds is a specialized trait, the authors compared the time parasitic and nonparasitic female birds spent on nests while laying eggs. Cowbirds typically spent less than 1 minute on host nests while laying. Rapid laying may be adaptive if aggressive behavior from the host can prevent cowbirds from successfully parasitizing the nest. Rapid laying may also increase the probability of egg acceptance by the host. The authors concluded that rapid laying by parasitic birds is an adaptation for parasitism and, in cowbirds, reduces the chances of attack.

Keywords: brood parasitism

Sealy, S. G. and R. C. Bazin. 1995. Low frequency of observed cowbird parasitism on eastern kingbirds: host rejection, effective nest defense, or parasite avoidance? Behav. Ecol. 6:140-145.

In this study, the authors attempt to determine whether cowbirds avoid parasitizing kingbirds, or whether the kingbirds eject the parasitic egg before it can be detected by the observer. Authentic cowbird eggs were artificially introduced into eastern kingbird nests during the pre-egg, early laying, late laying, and incubation stages. The authors conclude that cowbirds avoid parasitizing eastern kingbirds due to the kingbirds high rate of rejection. The kingbird rejection behavior persists due to the remote possibility of damaging or losing one of its own eggs (a maximum of 0.07 kingbird egg lost or damaged per cowbird egg ejected). The authors also suggest that this behavior may have evolved in response to conspecific rather than cowbird parasitism.

Keywords: host defense, host species

Sealy, S. G. and D. L. Neudorf. 1995. Male northern orioles eject cowbird eggs: implications for the evolution of rejection behavior. Condor 97:369-375.

Sixteen oriole nests were experimentally parasitized to determine the method of cowbird egg rejection, i.e., removal by spiking or by breaking the egg into pieces, and whether males remove cowbird eggs. At six nests, cowbird eggs were ejected by breaking them into pieces.

Males removed the cowbird egg from 2 nests, females removed the cowbird egg at 11 nests, and at 1 nest both participated in the removal of the cowbird egg.

Keywords: host defense, host species, Manitoba, Canada

Sealy, S. G. 1996. Evolution of host defenses against brood parasitism: implications of puncture-ejection by a small passerine. Auk 113:346-355.

In Manitoba, warbling vireos rejected eggs of the brown-headed cowbird from 1 naturally parasitized nest and 16 experimentally parasitized nests studied in 1992 and 1993. This report documents the first observations of puncture-ejection by the vireo, which is the smallest species (15 g) known to eject cowbird eggs in this manner. The authors prediction of the equilibrium hypothesis, that small hosts incur greater costs than large hosts when ejecting eggs, was examined by comparing the costs of rejection by experimentally parasitizing the nests of vireos and larger northern orioles.

Keywords: brood parasitism, host defense, Manitoba, Canada

Sealy, S. G. and J. C. Lorenzna. 1997. Feeding of nestling and fledgling brood parasites by individuals other than the foster parents: a review. Can. J. Zool. 75:1739-1752.

The authors summarize 67 reports of 13 species of brood-parasitic young being fed by individuals other than the host. They refer to this behavior as auxiliary feeding. The parasitic young benefits by receiving extra food, whereas the adult that feeds the parasite appears to behave maladaptively. The parasite may present a supernormal stimulus, manipulating unrelated adults into feeding it. Most of the auxiliary feedings were observed in brood parasites that were raised by small hosts.

Keywords: brood parasitism, host species

Sedgwick, J. A. and F. L. Knopf. 1988. A high incidence of brown-headed cowbird parasitism of willow flycatchers. Condor 90:253-256.

This note describes a high rate of cowbird parasitism within a population of willow flycatchers in the Arapahoe National Wildlife Refuge in north-central Colorado. The authors include details of responses to parasitism and host versus cowbird fledging success.

Keywords: brood parasitism, host species, Colorado

Selander, R. K. and D. R. Giller. 1960. First-year plumages of the brown-headed cowbird and red-winged blackbird. Condor 62:202-214.

In this study, first-year plumages of cowbirds and blackbirds were studied in detail. Juvenal feather retention in the Brewers blackbird and the common grackle is also discussed. The authors address four questions: (1) What percentages of juveniles of these species have an incomplete postjuvenal molt? (2) What is the extent of intra- and interspecific variation in types and numbers of juvenal feathers retained by first-year birds? (3) Is there evidence of correlation in first-year birds between numbers of feathers retained and age at molt? (4) What, if any, is the adaptive significance of individual variation in extent of the postjuvenal molt in icterids?

Keywords: morphology

Selander, R. K. and C. J. LaRue. 1961. Interspecific preening invitation display of parasitic cowbirds. Auk 78:473-504.

In this study the authors present and discuss the field records relating to the head-bowed behavior of cowbirds in 1959. This report deals almost entirely with preening invitation in the cowbird. The authors hope that this paper will stimulate other workers to observe and report further instances of this display by cowbirds in the field, since the significance of this behavior can be judged only when an abundance of field records are available.

Keywords: behavior

Selander, R. K. 1964. Behavior of captive South American cowbirds. Auk 81:394-402.

The author describes 16 hours of observations on the behavior of captive bay-winged, shiny, and brown-headed cowbirds in Washington, D.C.

Keywords: shiny cowbird, bay-winged cowbird, behavior

Shake, W. F. and J. P. Mattsson. 1975. Three years of cowbird control: an effort to save the Kirtland's warbler. Jack-Pine Warbler 53:48-53.

In May of 1972, cowbird traps were erected on seven major warbler nesting areas in north-central Michigan. A total of 2,200 cowbirds were removed over a 2-year trapping effort. The parasitism rate of warblers decreased to 9.5%, indicating the trapping program had been successful.

Keywords: population control, trapping, Michigan

Shankland, F. N. 1924. Some notes on the cowbird. Oologist 41:45-47.

The author gives a brief summary of the parasitic behavior of the cowbird.

Keywords: brood parasitism, behavior

Sharp, B. E. 1995. Brown-headed cowbirds and grazing on national forests in the Pacific Northwest. Northwestern Nat. 76:121-126.

Breeding Bird Surveys conducted between 1968 and 1990 indicate that cowbirds were abundant and their populations stable on national forests within the Pacific Northwest. Field surveys conducted in 1993 confirmed high cowbird numbers within riparian zones of the Umatilla National Forest. Relative cowbird abundance was higher in grazed and ungrazed riparian habitats than in fragmented forest. The author suggests that the high numbers of cowbirds should be considered an additional grazing program cost.

Keywords: abundance, Pacific Northwest, distribution

Sheppard, J. M. 1996. Nestling Kentucky warblers and cowbird attacked by brown-headed cowbird. J. Field Ornithol. 67:384-386.

An adult female brown-headed cowbird was flushed from a Kentucky warbler nest in 1988. The four warbler nestlings and lone cowbird nestling were apparently being attacked. This is at least the fifth report of nestling predation by brown-headed cowbirds.

Keywords: behavior, host species, Kentucky

Sherry, D. F. et al. 1993. Females have a larger hippocampus than males in the brood-parasitic brown-headed cowbird. Proc. Natl. Acad. Sci. 90:7839-7843.

The authors predicted that the spatial abilities required to locate and return accurately to host nests may favor female cowbirds based on the size of the hippocampal complex. Study results indicate that the size of the hippocampal complex, relative to size of the telencephalon, was greater in female cowbirds than it was in the males. No sex difference was found in red-winged blackbirds or the common grackle.

Keywords: physiology

Smith, C. P. 1926. Has the cowbird come to stay? Condor 28:245.

This paper describes multiple observations of nestling cowbirds in hosts nests, but none for adult cowbirds.

Keywords: host species

Smith, H. M. 1949. Irregularities in the egg-laying behavior of the eastern cowbird, Molothrus a. ater. J. Colorado-Wyoming Acad. Sci. 4:60.

This study discusses cowbird parasitism of red-winged blackbirds during the years of 1940-1941 and 1947-1948 in two widely separated areas: Illinois and Arkansas. The author describes how six cowbird eggs were laid with no chance of hatching; two were laid in abandoned nests, one was laid on cattail stalks immediately below a nest, two were deposited at least 6 days after incubation of the host eggs had been initiated, another was laid in a nest constructed the previous year.

Keywords: brood parasitism, eggs, Illinois, Arkansas

Smith, J. N. M. 1981. Cowbird parasitism, host fitness, and age of the host female in an island song sparrow population. Condor 83:152-161.

The author studied an isolated song sparrow population from 1975 to 1979, that was parasitized by one to three female cowbirds a year. Cowbird parasitism reduced the breeding success of adult female sparrows by 0.6 independent young per nest, and that of yearling females by 0.5 independent young per nest. Results also showed that cowbird parasitism reduced the total number of sparrow eggs within the nests of adult and yearling song sparrows by 0.8 and 0.5 eggs, respectively.

Keywords: host species, brood parasitism, British Columbia, Canada

Smith, J. N. M. and P. Arcese. 1994. Brown-headed cowbirds and an island population of song sparrows: a 16-year study. Condor 96:916-934.

The authors studied cowbird parasitism in a strongly fluctuating island population of song sparrows. One to three cowbird females visited the island on a daily basis to search for host nests in 13 of the 16 years of study. Although cowbirds colonized Mandarte Island, their presence had little effect on the sparrow population. The authors base this determination on several factors: (1) incomplete overlap in laying seasons; (2) multiple broods in sparrows; (3) functional and numerical responses of cowbirds to host density; (4) the sparrows ability to rear their young with young cowbirds; and (5) density-dependent host reproductive success.

Keywords: host species

Smith, P. W. and A. Sprunt IV. 1987. The shiny cowbird reaches the United States. American Birds 41:370-371.

This article summarizes the first account of the shiny cowbird in the United States in Florida on June 14, 1985.

Keywords: Shiny Cowbird, range expansion, Florida

Smith, W. F. 1921. The yellow-breasted chat and the cowbird. Bird-Lore 23:175-177.

A series of first-person accounts of cowbird parasitism of yellow-breasted chat nests in Connecticut.

Keywords: host species

Southern, W. E. and L. K. Southern. 1980. A summary of the incidence of cowbird parasitism in northern Michigan from 1911-1978. Jack-Pine Warbler 58:77-84.

In this paper, the authors reviewed existing data collected at the University of Michigan Biological Station between 1911 and 1978 to describe the relationship between the parasitic cowbird and 57 potential host species in northern Michigan. This study was unique in that it provides data on the frequency of cowbird parasitism for a single region over a span of 68 years.

Keywords: brood parasitism, host species, Michigan

Spaw, C. D. and S. Rohwer. 1987. A comparative study of eggshell thickness in cowbirds and other passerines. Condor 89:307-318.

Eggshell thickness of 3 brood parasitic Molothrus cowbirds, 17 other icterids, and 13 additional passerines was measured and compared. The authors determined that cowbirds lay eggs with shells that are 30% thicker than expected for their size. The authors propose that cowbirds have evolved to lay thick-shelled eggs that resist puncture and subsequent ejection by hosts that are too small to grasp the entire egg. Implications of the hypothesis concerning resistance to puncture ejection are also discussed.

Keywords: eggs

Spencer, R. A. 1985. Brown-headed cowbird fledgling feeding incidents.

C.F.O. Journal 19:39.

The author describes three incidents of host species feeding cowbird fledglings in Colorado in 1984.

Keywords: behavior, host species, Colorado

Stallman, H. R. and L. B. Best. 1996. Bird use of an experimental strip intercropping system in northeast Iowa. J. Wildl. Manage. 60:354-362.

Avian presence and use of an experimental strip intercropping pattern was evaluated in 1992-1993 by censusing birds along transects, observing birds from tower blinds, and monitoring the outcome of nests. Thirty-five bird species were observed using the strips. Brown-headed cowbirds and vesper sparrows were the two most abundant species. Only 4 of

the 35 species that used the experimental strips actually nested in the area. Of 40 nests found, 5 (12%) were lost to cowbird parasitism.

Keywords: brood parasitism, abundance, Iowa

Stamm, A. L. 1961. Cardinal feeding cowbird fledglings. Kentucky Warbler 37:58.

The observations of a cardinal feeding two cowbird fledglings in Kentucky in 1961 are presented in this paper.

Keywords: host species, Kentucky

Stamm, A. L. 1961. House sparrow victim of the cowbird. Kentucky Warbler 37:58-59.

This report is a first-person account of a house sparrow, a rare host, feeding a cowbird fledgling in Kentucky in 1960.

Keywords: host species

This report is based on the observations of a red-eyed vireo nest which was discovered on June 21, 1916, and contained two vireo eggs and one cowbird egg. The author discusses many aspects of the rearing of the brood, including behavior of hosts and parasite, feeding, regurgitation, number of feedings, food, and insights into instinct or intelligence governing behavior.

Keywords: host species ,life history, behavior

Stevenson, M. 1969. Agonistic behavior in the cowbird Molothrus ater. Ph.D. diss. Kansas State University, Manhattan.

Keywords: behavior

Stolzenburg, W. 1992. Cowbird roundup spares rare songbirds. Nature Cons. 42:page unknown.

A brief summary of a cowbird control effort in west-central Oklahoma to save the black-capped vireo in 1991.

Keywords: population control, Oklahoma

Stoner, E. A. 1919. Cowbird study in Iowa. Oologist 36:80-81.

This study is based on first-person observations of cowbird eggs in the nests of host species near Des Moines, Iowa, in 1907.

Keywords: host species, Iowa

Stoner, E. A. 1937. Cowbird breeding in Solano County, California. Condor 39:86.

A first-person account of a cowbird egg in the nest of a lazuli bunting, the first cowbird breeding record for this county, in 1936, is presented in this report.

Keywords: host species, range expansion

Strausberger, B. M. and M. V. Ashley. 1997. Community-wide patterns of parasitism of a host Ageneralist@ brood-parasitic cowbird. Oecologia 112:254-262.

Nest parasitism on a diverse avian community in northeastern Illinois was studied over the course of two breeding season. The study was conducted by implementing systematic nest searches throughout the study site which included a variety of grassland, forest-edge, and forest habitats. The results suggest that when presented with multiple hosts, the cowbird will parasitize host nests at a rate which balances its particular preference for a species, and the species nest defense capabilities. The authors developed a conceptual model that incorporates the observed correlation of cowbird eggs or nestlings with habitat, nest-type, host species body mass, and host behavioral defenses.

Keywords: brood parasitism, host species, model

Stutchbury, B. J. M. 1997. Effects of female cowbird removal on reproductive success of hooded warblers. Wilson Bull. 109:74-81.

Female brown-headed cowbirds were systematically removed from two adjacent warbler breeding populations for 2 to 5 years. In an adjacent area, where there was no cowbird control, the average percentage of nests parasitized was significantly higher than those areas where female cowbirds were removed. However, the reduction in parasitism rates did not significantly increase the number of young fledged per nest. The authors conclude that the effectiveness of cowbird removal as a management tool will likely vary with respect to cowbird abundance and the targeted host species, but this study suggests that the beneficial effects for the host species can be minimal.

Keywords: population control

Suarez, A. V., K. S. Fennig, and S. K. Robinson. 1997. Nesting success of a disturbance-dependent songbird on different kinds of edges. Conserv. Biol. 11:928-935.

In this study the authors compare the nesting success of a disturbance-dependent species, the indigo bunting, on different kinds of habitat edges at five sites (225 total nests) in southern Illinois from 1989 to 1993. Levels of brood parasitism by cowbirds varied significantly among sites and years, but not among edge types. The results of this study emphasize the need to reevaluate management practices (e.g., wildlife openings) that are designed to promote populations of disturbance-dependent wildlife.

Keywords: habitat, brood parasitism, Illinois

Talmadge, R. R. 1948. The cowbird moves northward in California. Condor 50:273-274.

First-person accounts of observations of cowbirds and nestlings in host nests in an area previously not within the known range of the cowbird are presented in this report.

Keywords: range expansion, California

Teather, K. L. and R. J. Robertson. 1985. Female spacing patterns in brown-headed cowbirds. Can. J. Zool. 63:218-222.

The authors of this study determined that although breeding female cowbirds at the Queens University Biological Station are often aggressive when encountering other females within their ranges, they do not defend exclusive territories. Aggression appears to be a function of two factors: females are more aggressive near the centers of their ranges than near its periphery, suggesting a gradient of aggression based on location within the females range; and females are most aggressive in woodland and marsh areas, and least aggressive in grassy areas and at artificial feeding stations. The author suggests that the aggression level of female cowbirds within territories and away from feeding areas is associated with the availability of host nests.

Keywords: territorial behavior

Teather, K. L. and R. J. Robertson. 1986. Pair bonds and factors influencing the diversity of mating systems in brown-headed cowbirds. Condor 88:63-69.

Observations of radio-tagged cowbirds by the authors indicate that individual males and females engage in extended associations through the breeding season. Persistent courtship by males directed toward specific females, in conjunction with extended periods where males and females were in close proximity with one another, suggests that cowbirds form pair bonds. Based on observations, the authors contend that the male is responsible for maintaining the pair bond. There were four cases of monogamy, as well as two bigamous and at least one trigamous relationship observed in the local population. The authors suggest that cowbird mating patterns may be influenced by both the sex ratio of the population as well as the habitat in which the populations are found.

Keywords: mating systems, radio telemetry

Teather, K. L. and P. J. Weatherhead. 1995. The influence of age and access to females on dominance in captive male brown-headed cowbirds (Molothrus ater). Can. J. Zool. 73:1012-1018.

Pairs of captive male cowbirds housed with a female formed clear dominance relationships. When yearling and adult males were housed together, the adult male was usually dominant. In one of ten controlled trials, the subordinate male became dominant without having access to a female for 48 hours, which suggests that access to a female was not the only reason for changes in status. Subordinate yearlings were as likely as subordinate adults to reverse their status. Size did not distinguish dominance from subordinate males or individuals that changed status from those that did not. However, subordinate males that became dominant displayed more when alone with the female than males that remained subordinate.

Keywords: behavior, social organization

Terborgh, J. 1992. Why American songbirds are vanishing. Scientific American 266:98-104.

The author gives an overview of the decline of many species of songbirds, and attributes part of the reason to cowbird parasitism.

Keywords: brood parasitism, host species

Terrill, L. M. 1961. Cowbird hosts in southern Quebec. Can. Field-Nat. 75:2-11.

In this study the author attempts to show the degree of parasitism suffered by each of the host victims, giving the number of occupied nests examined, the number and percentage of those parasitized, and the extreme dates recorded. Data used in this study is primarily that of the authors, which for a few host species, covers a period of more than 50 years.

Keywords: hosts species, brood parasitism, Quebec, Canada

Thomas, B. 1998. The hills have eyes. Nature Cons. 48:18-23.

In this article, the author discusses how high-tech monitoring is aiding in the recovery of endangered birds in Texas. In addition to miniature camera video, he describes the use of radio-telemetry to track brown-headed cowbird populations in an attempt to minimize parasitism on endangered species.

Keywords: population control, host species, radio telemetry, Texas

Thompson, C. F. and B. M. Gottfried. 1976. How do cowbirds find and select nests to parasitize? Wilson Bull. 88:673-675.

The author collected 20 inactive nests and placed them in typical nest sites in an old-field habitat on the Bachelor Estate of Miami University, Oxford, Ohio. Two quail eggs were placed in each nest to serve as Abait@ to entice cowbird parasitism. None of the experimental nests were parasitized, although cowbirds were common in the study area. These results support the theory that activity in the vicinity of host nest is important to female cowbirds when locating hosts nests and in determining which nests to parasitize.

Keywords: brood parasitism, nest-site selection, Ohio

Thompson, C. F. and B. M. Gottfried. 1981. Nest discovery and selection by brown-headed cowbirds. Condor 83:268-269.

The purposes of this note are to evaluate the current knowledge, to present additional evidence, and to encourage additional experimentation on the subject of discovery and selection of nests by cowbirds.

Keywords: nest-site selection

Thompson, F. R. III. 1994. Temporal and spatial patterns of breeding brown-headed cowbirds in the midwestern United States. Auk 111:979-990.

The author used radio-telemetry to study temporal patterns in cowbird behavior, habitat use, and sociality, as well as spatial patterns and movements of cowbirds among breeding, feeding, and roosting areas. An average of 42 locations of 84 radio-tagged female cowbirds was obtained on three study sites in Illinois and Missouri. Approximately 90% of the radio-tagged cowbirds established nonrandom, breeding, feeding, and roosting locations distributed within their home ranges. Cowbirds moved an average of 3.6 km between roosting and breeding locations, 1.2 km between breeding and feeding locations, and 2.6 km between feeding and roosting locations. The author concludes that cowbirds from midwestern populations exhibited similar commuting patterns between disjunct breeding and feeding areas as elsewhere in their range.

Keywords: behavior, habitat, movements, radio telemetry, Illinois, Missouri

Thompson, F. R. III. and W. D. Dijak. In press. Differences in movements, home range, and habitat preferences of female brown-headed cowbirds in three midwestern landscapes. In T. L. Cooke, S. K. Robinson, S. I. Rothstein, S. G. Sealy, and J.N.M. Smith (eds.). The ecology and management of cowbirds. University of Texas Press, Austin.

Keywords: habitat, movements

Thompson, F. R. III. In press. Biogeographic, landscape, and local factors affecting cowbird abundance and host parasitism levels. In T. L. Cooke, S. K. Robinson, S. I Rothstein, S. G. Sealy, and J.N.M Smith (eds.). The ecology and management of cowbirds. University of Texas Press, Austin, Texas.

Keywords: habitat, host species, brood parasitism

Thurber, W. A. and A. Villeda. 1980. Notes on parasitism by bronzed cowbirds in El Salvador. Wilson Bull. 92:112-113.

The author summarizes a series of observations of brood parasitism by bronzed cowbirds.

Keywords: bronzed cowbird, host species, El Salvador

Todd, H. O. 1936. The cowbird in summer near Murfreesboro. Migrant 7:72.

A first-person account of five species being parasitized by cowbirds from 1935 to 1936 is presented in this article.

Keywords: host species

Trail, P. W. and L. F. Baptista. 1993. The impact of brown-headed cowbird parasitism on populations of the Nuttall's white-crowned sparrow. Conserv. Biol. 7:309-316.

The authors report on the impact of cowbird parasitism on populations of white-crowned sparrows in the San Francisco Bay area. Using known mortality and fecundity values, they calculate that this population of sparrows cannot maintain its numbers when cowbird parasitism rates exceed approximately 20%. Therefore, the authors conclude that present parasitism levels appear to threaten the long-term survival of the Nuttalls white-crowned sparrow in the San Francisco area.

Keywords: brood parasitism, host species, California

Unglish, W. E. 1931. The dwarf cowbird in San Benito County, California. Condor 33:214. On May 10, 1931, cowbird eggs were discovered along the San Benito River near Betabel, California, in a golden pileolated warbler nest. These are the first records of the cowbird in this area.

Keywords: host species, range expansion, California

Uyehara, J. C. and P. M. Narins. 1995. Nest defense by willow flycatchers to brood-parasitic intruders. Condor 97:361-368.

In this report the authors analyze the adaptive value and specificity of willow flycatcher responses to simulated and live intrusions of brown-headed cowbirds. They hypothesized that flycatchers which are quieter near their nests are less likely to be parasitized than those that are more active and vocal. Parasitism was associated with the more active and vocal flycatcher pairs, suggesting that inconspicuous behavior was adaptive for this heavily parasitized population. When subjected to the calls of a brood parasite, the flycatchers responded by being quieter than they were to a playback of a nonparasitic species. Parasitized and unparasitized flycatchers did not differ in their response to female cowbird calls. Considering these results, the authors suggest that this population of willow flycatchers differentially recognized female cowbirds and differentially responded to female cowbirds, relative to the cowbirds distance from their nest.

Keywords: host defense, host species

Van Velzen, W. T. 1972. Distribution and abundance of the brown-headed cowbird. Jack-Pine Warbler 50:110-113.

A summary of the cowbirds distribution and abundance in the United States from Breeding Bird Survey data is presented in this report. It also provides the number of cowbirds recorded per route in each state and province along with the total number of routes run.

Keywords: abundance, distribution

Vasicek, J. M. 1935. A Savannah sparrow as a cowbird victim. Wilson Bull. 47:294.

This article documents an account of cowbird parasitism of the Savannah sparrow, with the host rejecting the egg by burying it, in 1935, in Cleveland, Ohio.

Keywords: host species, Ohio

Verner, J. and L. V. Ritter. 1983. Current status of the brown-headed cowbird in the Sierra National Forest. Auk 100:355-368.

The authors studied the seasonal distribution and abundance of cowbirds, their habitat preferences and use, and host relationships in the Sierra National Forest, California, in 1980 and 1981. From several hundred counts, including many made in 1978 and 1979, the relative numbers of cowbirds and potential hosts were estimated for a variety of habitats and for varying distances from established afternoon foraging aggregations. Since cowbirds were found to be rare, or absent in several major habitat types and areas remote from human-based food sources, the authors do not believe that any species populations in the Sierra Nevada are currently threatened by cowbird parasitism. However, the authors note that parasitism should be periodically monitored due to continuing human development in the mountains.

Keywords: abundance, distribution, California

Villeda, A. 1979. Rufous-collared sparrow victimized by bronzed cowbird. Wilson Bull. 91:628.

On July 4, 1977, in Guatemala City, Guatemala, the author observed a recently fledged bronzed cowbird following and begging food from a rufous-collared sparrow.

Keywords: bronzed cowbird, host species, Guatemala

Vogel, H. H. Jr. 1945. Cowbird parasitizes wood thrush and indigo bunting. Auk 62:633.

The author gives a record of a single parasitism event for the wood thrush and indigo bunting near Crawfordsville, Indiana, in 1943. Each nest had two cowbird eggs and three of the host species eggs. Both nests were lost, presumably to predation.

Keywords: host species, Indiana

Vogel, P. 1993. Who's seen the shiny cowbird? Gosse Bird Club 61:3-5.

A summary of the range expansion of the shiny cowbird and the prediction that the bird will soon appear in Jamaica are presented in this article.

Keywords: shiny cowbird, range expansion, Jamaica

Walkinshaw, L. H. 1949. Twenty-five eggs apparently laid by a cowbird. Wilson Bull. 61:82-85.

The author observed 25 similar eggs laid in nests over a 100-acre area in Pennfield Township, Calhoun County, Michigan, in 1944. It was concluded that the eggs came from the same female because (1) they were very similar in coloration, (2) no 2 were laid on the same day, (3) the length of 11 similarly colored eggs had significantly less variability than the length of 22 not-similarly colored eggs.

Keywords: brood parasitism, fecundity, laying rate, Michigan

Walkinshaw, L. H. 1961. The effect of parasitism by the brown-headed cowbird on Empidonax flycatchers in Michigan. Auk 78:266-268.

The author found three of the four Empidonax flycatchers had been parasitized by the cowbird in Michigan. Of 22 parasitized nests, 9 nests fledged 1 cowbird each and the host eggs did not even hatch.

Keywords: brood parasitism, host species, Michigan

Ward, D., A. K. Lindholm and J.N.M. Smith. 1996. Multiple parasitism of the red-winged blackbird: further experimental evidence of evolutionary lag in a common host of the brown-headed cowbird. Auk 113:408-413.

The authors tested whether a common host, the red-winged blackbird, accepts cowbird eggs in its nest because it does not recognize the cowbird egg as foreign (evolutionary-lag hypothesis) or since the cost of rejecting the eggs or deserting the nest and re-laying exceeds the benefits of egg rejection (evolutionary-equilibrium hypothesis). The authors tested these hypothesis by increasing the cost of acceptance by adding one, two, or three cowbird eggs to blackbird nests, and removing one host egg for every cowbird egg added. The authors found no rejection at any level of parasitism. The authors conclude that the evolutionary lag hypothesis applies to the red-winged blackbird.

Keywords: brood parasitism, eggs, egg manipulation

Ward, D. and J. N. M. Smith. 1998. Morphological differentiation of brown-headed cowbirds in the Okanagan Valley, British Columbia. Condor 100:1-7.

The authors investigated morphological variation in brown-headed cowbirds in the Okanagan Valley, southern British Columbia, Canada. They found that cowbirds from this region were significantly different in body measurements (wing, tail, tarsus, and culmen lengths) from both western subspecies, M. a. artemisiae and M. a. obscurus. The authors conclude that the Okanagan Valley cowbird population appears to have been present and isolated for sufficient time for morphological differentiation to occur. These findings question the hypothesis that many cowbird hosts do not recognize the cowbirds egg due to its recent arrival in parts of western North America.

Keywords: morphology, British Columbia, Canada

Weatherhead, P. J. and H. Greenwood. 1981. Age and condition bias of decoy-trapped birds. J. Field Ornithol. 52:10-15.

In this paper, the authors examine trapping bias relative to age, sex, and condition, using data collected from decoy-trapped blackbirds, starlings, grackles, and cowbirds in southern Quebec in 1979. The trapping data indicate that male cowbirds were captured in greater numbers than females, but do not provide information to determine whether trapping is age bias. Blackbirds were the only group captured in sufficient numbers both in the trap and the roost to allow testing for a condition bias. Also discussed are the implications of relying on baited traps as a means of capture which may have also biased these data.

Keywords: population control, trapping, Quebec, Canada

Weatherhead, P. J. and K. L. Teather. 1987. The paradox of age-related dominance in brown-headed cowbirds (Molothrus ater). Can. J. Zool. 65:2354-2357.

The objective of this study was to determine if dominance status of males was independent of age when they were competing for access to food. Adults were dominant in 54 of 66 dyads consisting of an adult and a yearling in which one individual won a significant proportion of their interactions. Results suggest that dominance status in one social arena may be a poor predictor of social status in another.

Keywords: social organization

Weatherhead, P. J. 1989. Sex ratios, host-specific reproductive success, and impact of brown-headed cowbirds. Auk 106:358-366.

The author examined cowbird parasitism of red-winged blackbird and yellow warbler nests to determine whether cowbird size (male vs. female) and host size (blackbirds vs. warblers) effect the growth and reproductive success of both the host and the cowbird. The impact of cowbirds was far greater on warblers than on blackbirds, primarily due to the poor competitive ability, and hence fledging success, of the warbler nestlings relative to the larger cowbird nestlings. In southern Manitoba, the level of negative impacts of cowbird parasitism

of warblers is likely to be maintained at a high level due to the abundant number of cowbirds fledged from blackbird nests.

Keywords: brood parasitism, Manitoba, Canada

Weatherhead, P. J. 1991. The adaptive value of thick-shelled eggs for brown-headed cowbirds. Auk 108:196-198.

The author discusses two hypotheses for the thicker eggshells of cowbirds: (1) thicker shells may be more resistant to attempts by the host to puncture the eggs, and (2) thicker shells protect cowbird eggs from cracking due to being stepped on by the female or due to bumping host eggs during laying or incubation. To test this hypothesis the author artificially parasitized the nests of red-winged blackbirds and yellow warblers in southern Manitoba and documented the results. The experiment with blackbirds did not support the hypothesis that thicker shells cause cowbird eggs to reduce competition in host nests by damaging host eggs. However, this hypothesis was supported in warblers, a much smaller species with more fragile eggs, although the specific role of eggshell thickness remains to be determined.

Keywords: eggs, egg manipulation, Manitoba, Canada

Weatherhead, P. J. and G. F. Bennett. 1992. Ecology of parasitism of brown-headed cowbirds by haematozoa. Can. J. Zool. 70:1-7.

The authors quantified haematozoa infections in 964 cowbirds sampled over 3 summers in eastern Ontario. The objective was to use the cowbird-haematozoa system to assess practical and theoretical aspects of testing Hamilton and Zuks hypothesis of sexual selection. The results suggest a number of pitfalls, some of which are potentially critical, to using haematozoa infections in passerines to test the Hamilton and Zuk hypothesis.

Keywords: physiology, Ontario, Canada

Webb, J. S. and D. K. Wetherbee. 1960. Southeastern breeding range of the brown-headed cowbird. Bird-Banding 31:83-87.

The discovery of juvenile cowbirds in Gainesville, Florida, on July 7 and July 28, 1958, is believed to constitute evidence that cowbirds breed farther southeast than previously believed. The known and suspected southeastern breeding range of the cowbird is plotted.

Keywords: range expansion, Florida

Webber, T. A. 1983. Allopreening by brown-headed cowbirds. Condor 85:249-250.

In this study the author reports that allopreening was common in a group of captive brown-headed cowbirds at the (Gainesville) Florida Field Station of the Denver Wildlife Research Center. If allopreening is not an artifact of captivity, its occurrence among cowbirds suggests that the interspecific head-down display arose in the intraspecific allopreening context, similar to that in other species of allopreening birds, and was then used in interspecific contexts.

Keywords: behavior, Florida

Webster, M. S. 1994. Interspecific brood parasitism of Montezuma oropendolas by giant cowbirds: parasitism or mutualism? Condor 96:794-798.

In this note, the author examines the possibility that a mutualistic relationship exists between giant cowbirds and one of their primary hosts in Costa Rica, the oropendola. He attempts to determined whether oropendolas exhibit nest defense behavior, and if so, have cowbirds developed a means to counteract against it. The results suggest that many populations of oropendolas and caciques defend against cowbird parasitism, and that the complex host-parasite mutualism is likely to be quite rare.

Keywords: giant cowbirds, brood parasitism, Costa Rica

West, M. J., A. P. King, D. H. Eastzer, and J.E.R. Staddon. 1979. A bioassay of isolate cowbird song. J. Comp. Physiol. Psychol. 93:124-133.

Captive female cowbirds, both reared in isolation, and captured in the wild, were exposed to experimentally manipulated versions of an isolate males song during the breeding season. Data show that a single song element, a brief note between the song phrases, plays a pivotal role in eliciting the females copulatory response to song. These data also demonstrate that relative amplitude variation and the fine structure within the interphrase unit affect the potency of a given song. Results suggest that the acoustic properties of this unit may account for the enhanced effectiveness of isolate song over normal cowbird song as a sex-unit releaser.

Keywords: vocalization

West, M. J. and A. P. King. 1980. Enriching cowbird song by social deprivation. J. Comp. Physiol. Psychol. 94:263-270.

Male cowbirds, juveniles and adults, were maintained in one of four conditions: (a) visual and auditory deprivation from males, (b) visual but not auditory deprivation, (c) social isolation, and (d) full contact with males. Their songs in the breeding season were tested with captive female cowbirds. The females responded with copulation postures most often to the songs of the males reared in conditions a and b. These results indicate the critical importance of the male cowbirds social environment for song potency.

Keywords: behavior, vocalization

West, M. J., A. P. King, and D. H. Eastzer. 1981. The cowbird: reflections on development from an unlikely source. American Scientist 69:56-66.

Evidence shows that male cowbirds exhibit vocal learning from an early age and continue to demonstrate it as adults. Data suggest that the normal development of cowbird song is derived from both genetic and experiential sources.

Keywords: vocalization

West, M. J., A. P. King, and D. H. Eastzer. 1981. Validating the female bioassay of cowbird song: relating differences in song potency to mating success. Anim. Behav. 29:490-501.

The purpose of this study was to validate the measure of song potency as the number of copulatory postures a song elicits by investigating its relationship to mating success. Two colonies of cowbirds during the breeding season were observed and their courtship behaviors

recorded. The results indicate a relationship between maximum song potency and mating success: the males that obtained the most copulations had songs of higher maximum potency and were the more dominant during the winter and early spring.

Keywords: behavior, vocalization

West, M. J., A. P. King, and T. J. Harrocks. 1983. Cultural transmission of cowbird song: measuring its development and outcome. J. Comp. Psychol. 97:327-337.

Bilingual cowbird males were created by exposing males of the eastern subspecies (M. a. ater) to males of the southern subspecies (M. a. obscurus) or to adult bilingual eastern birds raised in their hatching year with southern males. All juveniles became bilingual to differing degrees. Previously monolingual adults became bilingual only when the southern subspecies males and females were present. Data represent a strong quantitative demonstration that song learning can mediate selective mating and thus contribute to reproductive isolation.

Keywords: vocalization

West, M. J. and A. P. King. 1985. Social guidance of vocal learning by female cowbirds: validating its functional significance. Z. Tierpsychol. 70:225-235.

The authors provide data demonstrating that the songs of males, housed with females, are functionally, as well as acoustically, distinctive. The songs of eight groups of males were tested where the groups differed by age of singer, acoustic experience, and identity of social companion. The playback results demonstrate that nonsinging female cowbirds not only stimulate the male to modify song content, but song potency, thereby demonstrating the critical role female cowbirds may assume in the proximate and ultimate regulation of male vocal development.

Keywords: vocalization

West, M. J. and A. P. King. 1986. Song repertoire development in male cowbirds (Molothrus ater): its relation to female assessment of song potency. J. Comp.

Psychol. 100:96-303.

Keywords: vocalization

Whitcomb, R. F., C. S. Robbins, J. F. Lynch, B. L. Whitcomb, M. K. Klimkiewicz, and D. Bystrak. 1981. Effects of forest fragmentation on avifauna of the eastern deciduous forest. Pages 125-205 in R. L. Burgess and D. M. Sharpe (eds.). Forest island dynamics in man-dominated landscapes. Springer-Verlag, New York.

Keywords: habitat

White, L., E. Best, G. Clune, B. Marette, and J. Sechrist. 1998. Brown-headed cowbird control program: Virgin and Muddy Rivers, Nevada; Colorado River, Arizona. Bureau of Reclamation, Lower Colorado Regional Office, Boulder City, Nevada, and Technical Service Center, Denver Colorado.

This program was initiated in an attempt to reduce brood parasitism of the endangered southwestern willow flycatcher. Trapping and removal of brown-headed cowbirds was conducted at two sites within the Colorado River Basin from early-April to mid-June 1998. Neotropical migrant point counts were conducted in conjunction with the trapping effort. The distribution and abundance of cowbirds were evaluated and compared using the point count data. Results of the trapping effort and recommendations to assess the effectiveness of the trapping as a management tool to reduce the potential for parasitism are discussed.

Keywords: population control, trapping

White, S. B., R. A. Dolbeer, and T. A. Bookhout 1985. Ecology, bioenergetics, and agricultural impacts of a winter-roosting population of blackbirds and starlings. Wildl. Monog. 93.

The authors studied a major blackbird and starling roost near Milan, Tennessee, from November to mid-March of 1975-1976, 1976-1977, and 1977-1978. The objectives were to define the niches of each roosting species and to assess the impact of the birds on the surrounding agricultural community. Brown-headed cowbirds composed <2% of the roosting population. Their diet contained 74% weed seeds and 22% corn, most of which was obtained from pastures and adjacent feedlots.

Keywords: diet, Tennessee

Whitfield, M. J. 1990. Willow flycatcher reproductive response to brown-headed cowbird parasitism. M.S. thesis. California State University, Chico.

Keywords: brood parasitism, host species, California

Whitfield, M. J. and J. J. Placer. 1994. Brown-headed cowbird control program and monitoring for the southwestern willow flycatchers, South Fork Kern River, CA. Kern River Research Center, Final Report for CDFG Contract #FG 2285.

The authors removed 350 female cowbirds and 250 juveniles from the trap area in 1993. The trapping program was successful in meeting the goals of reducing cowbird parasitism and increasing willow flycatcher nest success. The parasitism rate dropped to an all-time low of 37.5% and the nest success increased to 44%. In addition, the parasitism rate was significantly lower in the trap area than in the nontrap area and the number of fledged young per nest attempt was higher in the trap area than in the nontrap area.

Keywords: population control, trapping

Whitfield, M. J. and C. M. Strong. 1995. A brown-headed cowbird control program and monitoring for the southwestern willow flycatcher, South Fork Kern River, California, 1995. California Department of Fish and Game, Bird and Mammal Conservation Program Rep. 95-4.

In this study the authors determine the effectiveness of cowbird trapping on the reproductive success of the endangered southwestern willow flycatcher. Following three years of cowbird trapping, the cowbird parasitism rate decreased from an average of 63.5% to 15.6% in the trap area. Results also reveal an increase in nest success, and in the number of young flycatchers fledged from the study area. The authors also discuss the more subtle impacts of cowbird parasitism, such as delayed fledging, and suggest other factors besides parasitism that may be limiting the recovery of the endangered flycatcher.

Keywords: population control, trapping, California

Whitfield, M. J. In press. Results of a brown-headed cowbird control program for the southwestern willow flycatcher. In T. L. Cook, S. K. Robinson, S. I. Rothstein, S. G. Sealy, and J. N. M. Smith (eds.). The ecology and management of cowbirds. University of Texas Press, Austin.

Keywords: population control, trapping, California

Wiener, L. Courtship behavior in M. a. ater and M. a. obscurus females. M.S. thesis, Duke University, Durham.

Keywords: behavior, mate selection

Wiens, J. A. 1963. Aspects of cowbird parasitism in southern Oklahoma. Wilson Bull. 75:130-139.

Purpose of this study was to investigate some of the major aspects of brood parasitism in the breeding avifauna of southern Oklahoma in 1960 and 1961. Particular emphasis was placed on the effects of cowbird parasitism on the host populations, the nesting success of the cowbird in relation to its hosts, and the nature of the laying period of the cowbird.

Keywords: brood parasitism, host species, Oklahoma

Wilcove, D. 1990. Empty skies. Nature Cons. 40:4-13.

This article discusses the declining songbird populations, primarily due to deforestation and cowbird parasitism.

Keywords: brood parasitism, host species

Wiley, J. W. 1982. Ecology of avian brood parasitism at an early interfacing of host and parasite populations. Ph.D. diss. University of Miami, Coral Gables.

Within mangrove habitat, 42% of the resident nonraptorial land bird species were parasitized by shiny cowbirds. The parasitized hosts produced 12% fewer eggs and fledged 67% fewer chicks than nonparasitized pairs. Chick growth rates of some parasitized host species were lower than nonparasitized nests.

Keywords: shiny cowbird, brood parasitism

Wiley, J. W. 1986. Growth of shiny cowbird and host chicks. Wilson Bull. 98:126-131.

The author monitored the growth of the shiny cowbird and its hosts in the Caribbean in 1980 and 1981. Due to the many disadvantages of parasitizing large species, cowbirds were expected to only rarely parasitize species larger than grackles.

Keywords: shiny cowbird, growth rate

Wiley, J. W. 1988. Host selection by the shiny cowbird. Condor 90:289-303.

Factors affecting shiny cowbird host selection were examined within the mangrove community in Puerto Rico from 1975 to 1981. The author found that cowbirds did not parasitize their potential hosts in proportion to their abundance. Cowbirds located host nests primarily by secretly observing their activities in suitable nesting habitat. The cowbirds appeared to use nest building and territorial defense activities as cues to nest location and status.

Keywords: shiny cowbird, host selection, brood parasitism, Puerto Rico

Williams, C. S. and A. H. Trowbridge. 1939. Wilsons phalarope host of Nevada cowbird. Auk 56:77.

On June 6, 1938, while the authors were conducting a waterfowl survey on the Bear River Refuge in Utah, two nests of Wilsons phalarope, both parasitized by the Nevada cowbird, were found.

Keywords: host species, Utah

Williams, R. E. and W. B. Jackson. 1981. Dietary comparisons of red-winged blackbirds, brown-headed cowbirds, and European starlings in north-central Ohio. Ohio J. Sci. 81:217-225.

Stomach contents from 99 blackbirds, 97 cowbirds, and 69 starlings were collected and compared along the southern shores of Lake Erie in north-central Ohio. The stomach contents for redwing blackbirds, brown-headed cowbird, and European starlings were: agricultural products 73.9%, 54.8%, and 28.1%; and animal material 7.6%, 3.4%, and 30.3%, respectively. Insects comprised 13.5% of the starling diet but were far less important to the diets of redwings and cowbirds.

Keywords: diet, Ohio

Wolcott, R. H. 1899. Red-winged blackbird and cowbird. Bull. Michigan Ornithol. Club 3:18.

A first-person account of blackbirds being commonly parasitized by cowbirds in Nebraska, but rarely so in Michigan. The author describes one observation of a blackbird burying a cowbird egg.

Keywords: host species, Nebraska, Michigan

Wolf, L. 1987. Host-parasite interactions of brown-headed cowbirds and dark-eyed juncos in Virginia. Wilson Bull. 99:338-350.

In the Allegheny Mountains of Virginia, 39% of junco nests found in this study contained at least one cowbird egg. Junco nests located in the more open areas were more heavily parasitized and predated than those that were located in denser vegetation. Cowbirds laid an average of 1.7 eggs, and removed an average of 1.2 junco eggs per nest. When only one cowbird nestling was present in the parasitized nests, junco nestlings appeared to develop as well as nestlings in the unparasitized nests. Cowbirds are recent invaders in this area, and possible anti-parasite adaptations are discussed.

Keywords: brood parasitism, laying rate, Virginia

Wolfe, D. H. 1994. Brown-headed cowbirds fledged from barn swallow and American robin nests. Wilson Bull. 106:764-766.

In this article the author describes the observations of swallows and robins raising cowbirds at least to fledgling age.

Keywords: host species

Wolfe, D. H. 1995. Brown-headed cowbird parasitism of northern mockingbirds in Oklahoma. Bull. Oklahoma Ornithol. Soc. 28:7-8.

In this report the author documents mockingbirds (a rare host in Oklahoma) fledging cowbird chicks in 1994.

Keywords: brood parasitism, host species, Oklahoma

Wolfe, D. H. 1996. Brown-headed cowbirds fledge from a Louisiana waterthrush nest. Bull. Oklahoma Ornithol. Soc. 29:15-16.

The author reports on the first record of cowbirds parasitizing this species in Oklahoma in 1995.

Keywords: brood parasitism, host species, range expansion, Oklahoma

Wood, D. R. and E. K. Bollinger. 1997. Egg removal by brown-headed cowbirds: a field test of the host incubation efficiency hypothesis. Condor 99:851-857.

The authors tested the hypothesis that the incubation efficiency of a parasitic cowbird egg is affected by the size and number of host eggs. A single house sparrow or brown-headed cowbird egg was added to each host nest, and in some nests a host egg was removed. The hatching success and incubation period for each of the experimental nests were recorded. The results did not significantly support the incubation efficiency hypothesis to explain host-egg removal by brown-headed cowbirds.

Keywords: egg manipulation

Woods, R. S. 1930. Two more victims of the cowbird. Condor 32:126.

The author adds two more species to those listed by Friedmann (1929) as hosts of the cowbird: the green-backed goldfinch and the black-tailed gnatcatcher. These were recorded at Azusa, California, between 1927 and 1928.

Keywords: host species, California

Woodward, P. W. 1979. Survival of fledgling brown-headed cowbirds. Bird Banding 50:66-68.

While studying the behavior and ecology of fledgling cowbirds and their hosts in Fairfax County, Virginia, and Montgomery County, Maryland, in 1974 to 1976, the authors were able to determine the survival rate of fledgling cowbirds up to the time of attaining independence at 25 to 39 days of age. The survival rate of 21 banded nestling cowbirds was 47.6%. Probable causes of death were predation (6 cases), drowning (1), and automobile collision (1).

Keywords: mortality, Maryland

Woodward, P. W. 1979. Brown-headed cowbird parasitism on eastern bluebirds. Wilson Bull. 91:321-322.

The cowbird parasitism rates on a small population of eastern bluebirds in Reston, Virginia, were determined to be relatively high. The suspected reasons for high parasitism in this population were a high host density and conspicuous nest boxes.

Keywords: brood parasitism, host species, Virginia

Woodward, P. W. 1983. Behavioral ecology of fledgling brown-headed cowbirds and their hosts. Condor 85:151-163.

In this study the author monitored the behavior of 22 cowbird fledglings, raised by 9 host species, during the period of leaving the nest and independence. The objectives were: to document the development of the fledgling during this period; to determine if fledglings behaved differently with different hosts; and to determine if fledgling cowbirds possess adaptations for brood parasitism. The authors believed that the general development of the cowbird fledglings was not modified by the various hosts. Fledgling cowbirds were fed more often by their adult hosts, than were the hosts own young. The loud, persistent begging exhibited by the fledgling cowbirds, which likely results in them receiving a greater portion of the available food, is probably the cowbirds main adaptation for brood parasitism. Keywords: behavior

Woodworth, B. L. 1997. Brood parasitism, nest predation, and season-long reproductive success of a tropical island endemic. Condor 99:605-621.

To determine the impact of the shiny cowbird on vireo reproductive success, the author studied the demography of marked Puerto Rican vireos in Guanica Forest, Puerto Rico, from 1990 to 1993. The author concludes that the Puerto Rican vireo may be in danger of extirpation from portions of its historic range. This assumption is based on the combination of a restricted breeding season, high predation and parasitism rates, reduced population recruitment as a result of parasitism, and low seasonal fecundity of females.

Keywords: shiny cowbird, host species, brood parastism, Puerto Rico

Yahner, R. H. and C. A. DeLong. 1992. Avian predation and parasitism on artificial nests and eggs in two fragmented landscapes. Wilson Bull. 104:162-168.

The authors tested the hypothesis that avian predation and parasitism on artificial arboreal nests (natural nests containing artificial eggs of two color patterns) did not differ between uncut-clear-cut forest and forest-farmland landscapes. In addition, they tested whether the use of ceramic eggs, which simulate natural eggs in terms of color and size, could be used as a means of assessing avian predation and parasitism. Differential rates of nest disturbance by avian and mammalian predators at the two sites were not unexpected because blue jays were more common at one site, and raccoons were more prevalent at the other site. Abundance of cowbirds was similar at both sites.

Keywords: brood parasitism, egg manipulation

Yamauchi, A. 1995. Theory of evolution of nest parasitism in birds. Amer. Nat. 145:434-456.

In this article, the evolutionary dynamics of both intra- and interspecific parasitism are analyzed by using a quantitative genetic model. The model considers four traits: recognition ability for conspecific eggs, clutch size, total parasitism rate, and interspecific parasitization rate.

Keywords: brood parasitism, evolution, model

Yokel, D. A. 1986. Monogamy and brood parasitism: an unlikely pair.

Anim. Behav. 34:1348-1358.

Intensive observation of a population of brown-headed cowbirds, including 114 marked birds, demonstrated that monogamy is the most prevalent mating system. This study provides strong evidence that the cowbirds mating system varies geographically, since the only similar study previously conducted demonstrated promiscuity.

Keywords: mating system

Yokel, D. A. 1986. The social organization of the brown-headed cowbird in the Owens Valley, California. Pages 164-172 in Hall, C. A. Jr., and D. J..Young (eds.). Natural history of the White-Inyo Range, eastern California and western Nevada and high altitude physiology. University of California, White Mountain Research Station Symposium, Vol. 1. Regents of the University of California, Los Angeles.

The author studied the behavior of the brown-headed cowbird during the 1982-1985 breeding seasons along the Owens River near Bishop, California. The results indicate that neither the male nor female cowbirds defend exclusive breeding ranges, and the primary mating system is monogamous, although a few males may mate bigamously. The authors also discuss the demography and patterns of spacing and mating.

Keywords: mating system, California

Yokel, D. A. 1987. Sexual selection and the mating system of the brown-headed cowbird (Molothrus ater) in eastern California. Ph.D. diss., University of California, Santa Barbara.

The author studied the behavior of brood parasitic brown-headed cowbirds during the 1982-1985 breeding seasons along the Owens River near Bishop, California, and along Mammoth Creek 65 km to the northwest. The author determined that: neither males nor females defended exclusive breeding ranges; although monogamy was the most prevalent, a few males mated bigamously; and adult males had much greater mating success than yearling males. Abstract only.

Keywords: mating system, California

Yokel, D. A. 1989. Intrasexual aggression and the mating behavior of brown-headed cowbirds: their relation to population densities and sex ratios. Condor 91:43-51.

The author describes population densities, sex ratios, and the social behavior of cowbirds at two sites in eastern California in 1983 and 1984. Sex ratios between the two sites were similar, but differed from those observed elsewhere. Population densities varied between these two sites and elsewhere. Although the level of intrasexual aggression among females differs between the study areas, female territoriality was absent. The author suggests that the variation in the local social behavior of the cowbirds may be correlated with population density, rather than sex ratio; and in low density cowbird populations, selection may favor aggression among females, monogamy, and more frequent mate attendance by males.

Keywords: behavior, social organization, California

Yokel, D. A. 1989. Payoff asymmetries in contests among male brown-headed cowbirds. Behav. Ecol. Sociobiol. 24:209-216.

Morphometric analyses and behavioral observations of a marked population of cowbirds revealed several male attributes correlated with dominance. Age and involvement in more contests exerted significant partial effects in some analyses, but only the presence of a potential female mate did so on a consistent basis. The author suggests that a female is of greater value to the male she consorts with than she is to other males. The females presence during contests was found to induce the male to persist (or escalate) and to dominate his male opponents.

Keywords: behavior, social organization

Yokel, D. A. and S. I. Rothstein. 1991. The basis for female choice in an avian brood parasite. Behav. Ecol. Sociobiol. 29:39-45.

Behavioral observation and experimental manipulation of a marked population of cowbirds were conducted to determine whether or not females exhibit mate choice and to clearly determine the ultimate basis for mate selection. The observed patterns of female aggression toward males revealed that females do have the opportunity to display choice. However, no conclusive evidence that a male provided his mate with protection from harassment by other males was found; nor was there any indication that males provide females with other closely related benefits or services. An experimental removal of mated males and the pattern of subsequent remating of the females were observed to be consistent with female choice for male genetic quality.

Keywords: mate selection

Young, H. 1949. Robin accepts cowbird egg. Passenger Pigeon 11:132.

On May 23, 1949, in Madison, Wisconsin, the author discovered a robin nest containing two eggs of the host and one cowbird egg. The robin eggs successfully hatched and the chicks fledged, but the cowbird egg never hatched.

Keywords: host species, Wisconsin

Young, H. F. 1963. Breeding success of the cowbird. Wilson Bull. 75:115-121.

In this study the author presents the results on the hatching and fledging success of 879 cowbird eggs from 580 nests of 36 host species in Wisconsin in 1959 and 1960. Fledging success was distinctly better than hatching success, and overall reproductive success was 25%. The fledging rate for eggs laid in the nests of heavily parasitized species was 25%. Keywords: brood parasitism, host species, Wisconsin

Zimmerman, J. L. 1983. Cowbird parasitism of dickcissels in different habitats and at different nest densities. Wilson Bull. 95:7-22.

The nesting success of dickcissel populations from old field and prairie habitats of Kansas were analyzed to: determine the impacts of cowbird parasitism; assess the productivity of brown-headed cowbirds from dickcissel nests; and test Fretwells (1977) hypothesis that the frequency and intensity of cowbird parasitism were inversely related to host nest density. Fretwells hypothesis was supported by the study results; both the frequency of cowbird parasitism and intensity were inversely associated with the density of host nests. This relationship also explains the habitat difference in parasitism since dickcissel densities were found to be lower in the prairie habitat.

Keywords: host species, brood parasitism, Kansas