Distribution and Abundance
- BBS Map |
- Breeding range entire United States, southern Canada and
- Before European settlement, range limited to open grasslands of
central North America; spreading east in early 1800s as forests were cleared,
creating open habitat for expansion (Mayfield 1965). Similar expansion west in
the 1900s (Rothstein et al. 1980, Laymon 1987).
- Short-distance migrant within North America; seasonal migration between
breeding and wintering distributions. Northeast U.S. birds travel about
800-850km between breeding season banding and winter recovery (Dolbeer 1982).
- Winter range in eastern, southern central, and west coast United States; into Mexico.
- Prefers habitats with low or scattered trees among
grassland vegetation including woodland edges, brushy thickets, prairies,
fields, pastures, orchards, and residential areas. Wood-field ecotones preferred
over either extensive woods or extensive field or prairie areas (Gates and
Gysel 1978, Brittingham and Temple 1983, Johnson and Temple 1990).
- In Wisconsin, of 1375 observations from 1995-2000 where habitat type was
reported, 25% were in upland hardwood shrub (particularly hedgerows) or upland
23% were in urban areas, 19.5% were in upland hardwood forests (particularly
oak) or upland mixed forests, and 14% in upland open areas (WSO 2002). In Michigan,
one-third of all observations from 1983-1988 were in
residential-roadside-hedgerow habitats (Brewer et al. 1991).
- Forages on ground, rarely in vegetation; frequently in association with
ungulates which disturb insect prey.
- Migratory roost sites generally early successional forest, 18-34 years-old, often high
density stands of red maple and sweetgum with compact enclosed canopies (Lyon
and Caccamise 1981).
- In winter, generally found at the margins in areas with
deciduous trees (Robertson et al. 1978).
- Diet predominately seeds and arthropods.
- Populations vary in primary type of mating system
(promiscuous, polygynous, polyandrous or monogamous), possibly in relation to
population sex ratios (Teather and Robertson 1986) or population density
(Yokel 1989). Pairs may continue over successive years (Dufty 1982).
- Mated males guard females from courtship behavior of other males (Yokel
1986, 1989) and respond aggressively to calls of other males (Rothstein et al.
1988); defense but not mutual exclusion of territories (Teather and Robertson
- Females respond to calls of other females with aggressive approaches (Darley
1982, Yokel 1989), but laying ranges overlap (Fleischer 1985); thus more than
one female may lay in the same host nest. Feeding areas overlap laying ranges;
more so in eastern studies (Darley 1982, 1983; Dufty 1982).
- Birds can travel several kilometers between foraging sites, areas with little or short vegetation (such as lawns), and nests that
are parasitized (references).
- No indication of interspecific territoriality.
- Gregarious, often found in mixed-species flocks of blackbirds.
Parasitism and Predation
- Over 220 host species have been reported as parasitized; 144 species have
reared cowbird young (Friedmann et al. 1977, Friedmann and Kiff 1985).
- Many bird species respond aggressively to Brown-headed Cowbirds, an
indication that hosts can identify cowbirds as a threat to their own
reproductive success (Robertson and Norman 1976, 1977; Folkers and Lowther
1985, Smith et al. 1984, Burgham and Picman 1989).
- In Wisconsin, of confirmed breeding observations from 1995-2000, the top
hosts were Chipping Sparrow and Song Sparrow (WSO 2002). In Michigan, of
confirmed breeding observations from 1983-1988, the top host was Kirtland's
Warbler, then Field Sparrow and Chipping Sparrow (Brewer et al. 1991).
- Parasitism rates tend to be relatively low in largely intact forested landscapes of northern Michigan, Wisconsin and Minnesota
- Egg and nestling loss for the cowbird reflects nest predation on the host
species. Rejection of cowbird eggs occurs by either ejecting cowbird eggs from the nest,
burying cowbird eggs under a new nest lining, or deserting the nest. Certain
species (Eastern Kingbird, Blue Jay, American Robin, Gray Catbird, Brown
Thrasher, Cedar Waxwing, Northern Oriole) almost always reject cowbird eggs.
Most other hosts reject less frequently, less than 20% of the time (Rothstein
1975). Species may include both rejector and acceptor populations depending on
overlap in distribution with cowbirds (Briskie et al. 1992).
- Specific predators of fledglings include black racers, black rat snake, and
Blue Jays (Woodward and Woodward 1979).
Conservation and Management
- Forest interior species, formerly isolated from cowbird parasitism by habitat, became
exposed to parasitism as forest fragmentation increased edge and provided access
to cowbirds (Brittingham and Temple 1983).
- Brood parasitism imposes additional mortality on host populations, but stable
equilibria are achieved if parasitism rates remain below some critical level
(May and Robinson 1985).
- Present concerns involve species with small populations (e.g., Kirtland's
Warbler, Black-capped Vireo, Least Bell's Vireo).
- Management plans involve
trapping and removing cowbirds from host breeding areas (Walkinshaw 1983,
Grzybowski et al. 1986).
- BBS trend results from 1966-2000 (Sauer et al. 2001) in the Northern Spruce-Hardwoods region indicate a significant population decline of
the Brown-headed Cowbird
in this region (-5.6, p=0.00 Trend
Graph S28), as is the case in the Great Lakes Transition region (-2.4,
Graph S20). Survey-wide (US and Canada), this species has shown a slight but
decline (-1.0, p=0.00 Trend
For more information about the management of the Brown-headed Cowbird, please
see the Species
Management Abstract, from the Conserve
Online public library, maintained by The Nature Conservancy.
This species account is based on: Lowther, P.E. 1993. Brown-headed Cowbird. In
The Birds of North America, No. 47 (A. Poole and F. Gill, eds.). The Academy of
Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union,
- Brewer, R., G.A. McPeek and R.J. Adams, Jr. 1991. The atlas of breeding
birds of Michigan. Michigan State University Press, East Lansing.
- Briskie, J.V., S.G. Sealy and K.A. Hobson. 1992. Behavioral defenses against
avian brood parasitism in sympatric and allopatric host populations. Evolution
- Brittingham, M.C. and S.A. Temple. 1983. Have cowbirds caused forest
songbirds to decline? BioScience 33:31-35.
- Burgham, M.C.J. and J. Picman. 1989. Effect of Brown-headed Cowbird on the
evolution of Yellow Warbler anti-parasite strategies. Animal Behavior
- Darley, J.A. 1982. Territoriality and mating behavior of the male
Brown-headed Cowbird. Condor 84:15-21.
- Darley, J.A. 1983. Territorial behaviour of the female Brown-headed Cowbird.
Can. J. Zool. 61:65-69.
- Dolbeer, R.A. 1982. Migration patterns for age and sex classes of blackbirds
and starlings. J. Field Ornithol. 53:28-46.
- Dufty, A.M., Jr. 1982. Movements and activities of radio-tracked
Brown-headed Cowbirds. Auk 99:319-327.
- 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.
- Folkers, K.L. and P.E. Lowther. 1985. Responses of Red-winged
Blackbirds and Yellow Warblers to Brown-headed Cowbirds. J. Field Ornithol.
- Friedmann, H. and L.F. Kiff. 1985. The parasitic cowbirds and their hosts.
Proc. West. Found. Vert. Zool. 2:225-304.
- Friedmann, H., L.F. Kiff and S.I. Rothstein. 1977. A further contribution to
knowledge of the host relations of the parasitic cowbirds. Smithsonian Contr.
- Gates, J.E. and L.W. Gysel. 1978. Avian nest dispersion and fledging success
in field-forest ecotones. Ecology 59:871-883.
- Grzybowski, J.A., R.B. Clapp and J.T. Marshall, Jr. 1986. History and
current population status of the Black-capped Vireo in Oklahoma. Amer. Birds
- Johnson, R.G. and S.A. Temple. 1990. Nest predation and brood parasitism of
tallgrass prairie birds. J. Wildl. Manage. 54:106-111.
- Laymon, S.A. 1987. Brown-headed Cowbirds in California: historical
perspectives and management opportunities in riparian habitats. West. Birds
- Lyon, L.A. and D.F. Caccamise. 1981. Habitat selection by roosting
blackbirds and starlings: management implications. J. Wildl. Manage.
- May, R.M. and S.K. Robinson. 1985. Population dynamics of avian brood
parasitism. Amer. Nat. 126:475-494.
- 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.
- Robertson, R.J. and R.F. Norman. 1977. The function and evolution of
aggressive host behavior towards the Brown-headed Cowbird. Can. J. Zool.
- Rothstein, S.I. 1975. Evolutionary rates and host defenses against avian
brood parasitism. Amer. Nat. 109:161-176.
- 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
- Sauer, J.R., J.E. Hines and J. Fallon. 2001. The North American Breeding
Bird Survey, Results and Analysis 1966-2000. Version 2001.2, USGS
Patuxent Wildlife Research Center, Laurel, MD.
- Smith, J.N.M., P. Arcese and I.G. McLean. 1984. Age, experience, and enemy
recognition by wild Song Sparrows. Behav. Ecol. Sociobiol. 14:101-106.
- Teather, K.L. and R.J. Robertson. 1985. Female spacing patterns in
Brown-headed Cowbirds. Can. J. Zool. 63:218-222.
- 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.
- Walkinshaw, L.H. 1983. Kirtland's Warbler: the natural history of an
endangered species. Cranbrook Inst. Sci. 58.
- Wisconsin Society for Ornithology. 2002. Wisconsin
Breeding Bird Atlas.
- Woodward, P.W. and J.C. Woodward. 1979. Survival of fledgling Brown-headed
Cowbirds. Bird-Banding 50:66-68.
- Yokel, D.A. 1986. Monogamy and brood parasitism: an unlikely pair. Anim.
- Yokel, D.A. 1989. Intrasexual aggression and the mating behavior of
Brown-headed Cowbirds: their relation to population densities and sex ratios.