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Brown-headed Cowbird -
Native Species Global Rank
Agency Status USFWS
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Length: 19 cm; heavy conical bill and a brown iris; walks with the squared tail uptilted. Adult male has a plain brown head, neck, and upper chest, with the rest of the plumage glossy greenish black. Adult female is gray-brown above, paler below. Juvenile is paler above, heavily streaked below, with pale edgings on the feathers on the back; young males molting to adult plumage are patchy black, brown, and buff; mass of adult male is 39 to 57 g, female is smaller. EGGS: vary from pure white to bluish-white; entire egg is covered with chocolate brown or yellowish-tan specks or blotches, which are often heaviest around the larger end (Friedmann 1929). Eggs average 21.5 by 16.4 mm (Bent 1958), with a mass of 3.2 to 3.4 g (Walkinshaw 1983).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see
Marks et al. 2016, Birds of Montana.
Western Hemisphere Range
Observations in Montana Natural Heritage Program Database
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
SUMMER (Feb 16 - Dec 14)
Direct Evidence of Breeding
Indirect Evidence of Breeding
No Evidence of Breeding
WINTER (Dec 15 - Feb 15)
Not Regularly Observed
(Observations spanning multiple months or years are excluded from time charts)
In the Bozeman area, normal migration periods are May 8 to 30 with no discernible movement in the fall.
Species prefers areas with low or scattered trees among grassland vegetation—woodland edges, brushy thickets, prairies, fields, pastures, orchards, or even residential areas.
Ecological Systems Associated with this Species
Details on Creation and Suggested Uses and Limitations
How Associations Were Made
We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.
In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.
However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system,
point observations were associated with that system.
Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.
The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.
If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.
Suggested Uses and Limitations
Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.
These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at:
) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.
Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.
Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.
Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).
Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.
Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998. Montana atlas of terrestrial vertebrates. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT. 1302 p.
Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
Commonly Associated with these Ecological Systems
Forest and Woodland Systems
Human Land Use
Recently Disturbed or Modified
Shrubland, Steppe and Savanna Systems
Wetland and Riparian Systems
Occasionally Associated with these Ecological Systems
Forest and Woodland Systems
Sparse and Barren Systems
Wetland and Riparian Systems
Diet consists mainly of anthropods and seeds.
Species is a brood parasite; nests are chosen by females, but are that of another species. Care given to cowbird eggs and young is provided by the host and reflects characteristics of that species. Brood consists of four to five eggs; incubation time 10 to 13 days. Young able to fly 10 to 11 days after hatch.
Literature Cited Above
Legend: View Online Publication Bent, A.C. 1958. Life histories of North American blackbirds, orioles, tanagers, and their allies. U.S. Natl. Mus. Bull. 211. Washington, D.C. Friedmann, H. 1929. The cowbirds: a study in the biology of social parasitism. Charles C. Thomas, Publisher, Springfield, Illinois. Marks, J.S., P. Hendricks, and D. Casey. 2016. Birds of Montana. Arrington, VA. Buteo Books. 659 pages. Walkinshaw, L.H. 1983. Kirtland's warbler: the natural history of an endangered species. Cranbrook Institute of Science, Bloomfield Hills, Michigan. 207 pp. Additional References
Legend: View Online Publication Do you know of a citation we're missing? Airola, D.A. 1986. Brown-headed cowbird parasitism and habitat disturbance in the Sierra Nevada. J. Wildl. Manage. 50: 571-575. American Ornithologists’ Union [AOU]. 1998. Check-list of North American birds, 7th edition. American Ornithologists’ Union, Washington, D.C. 829 p. Baril, L.M. 2009. Change in deciduous woody vegetation, implications of increased willow (Salix spp.) growth for bird species diversity, and willow species composition in and around Yellowstone National Park's northern range. M.Sc. Thesis. Bozeman, Montana: Montana State University. 124 p. Becker, D.M. 1984. Reproductive ecology and habitat utilization of Richardson's merlins in southeastern Montana. M.Sc. Thesis. Missoula, MT: University of Montana. 62 p. Bird Conservancy of the Rockies. 2017. Pocket Guide to Northern Prairie Birds. Brighton, CO: Bird Conservancy of the Rockies. 98 p. Bramblett, R.G., and A.V. Zale. 2002. Montana Prairie Riparian Native Species Report. Montana Cooperative Fishery Research Unit, Montana State University - Bozeman. Brittingham, M.C. and S.A. Temple. 1983. Have cowbirds caused forest songbirds to decline? BioScience 33: 31-35. Cameron, E. S. 1907. The birds of Custer and Dawson counties, Montana. Auk 24(3):389-406. Casey, D. 2005. Rocky Mountain Front avian inventory. Final report. Prepared for the U.S. Fish and Wildlife Service and The Nature Conservancy by the American Bird Conservancy, Kalispell, Montana. Clawson, M.R. 199. An investigation of factors that may affect nest success in CRP lands and other grassland habitats in an agricultural landscape. M.Sc. Thesis. Bozeman, MT: Montana State University. 45 p. Cobell, B. and R. Wagner. 2002. An evaluation of the terrestrial and aquatic resources of Malmstrom Air Force Base. USFWS - Montana Fish and Wildlife Management Assistance Office. 28 pgs + append. Confluence Consulting Inc. 2011. Montana Department of Transportation Wetland Mitigation Monitoring Reports (various sites). MDT Helena, MT. Confluence Consulting Inc. 2012. Montana Department of Transportation Wetland Mitigation Monitoring Reports (various sites). MDT Helena, MT. Dickson, D.C. 1991. Systematic wildlife observations on the Blackfoot-Clearwater Wildlife Management Area. Montana Department of Fish, Wildlife and Parks. Missoula, MT. 14 pp. plus appendices and photographs. Dood, A.R. 1980. Terry Badlands nongame survey and inventory final report. Montana Department of Fish, Wildlife, and Parks and Bureau of Land Management, Helena, MT. 70 pp. DuBois, K.L. 1979. An inventory of the avifauna in the Long Pines of Southeastern Montana. M.Sc. Thesis. Bozeman, MT: Montana State University. 113 p. Econ, Inc. 1988. Wildlife monitoring report, 1987 field season, Big Sky Mine. March 1988. In Peabody Mining and Reclamation Plan Big Sky Mine Area B. Vol. 8, cont., Tab 10 - Wildlife Resources. Appendix 10-1, 1987 Annual Wildlife Report. Ehrlich, P., D. Dobkin, and D. Wheye. 1988. The birder’s handbook: a field guide to the natural history of North American birds. Simon and Schuster Inc. New York. 785 pp. Faanes, C.A. 1983. Breeding birds of wooded draws in western North Dakota. Prairie Nat. 15(4): 173-187. Finch, D.M. 1991. Positive associations among riparian bird species correspond to elevational changes in plant communities. Canadian Journal of Zoology 69:951-963. Fjell, Alan K., and Brian R. Mahan., 1983, Peabody Coal Company Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1982 field season. May 1983. Fjell, Alan K., and Brian R. Mahan., 1985, Peabody Coal Company Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1984 field season. February 1985. Gates, J.E. and L.W. Gysel. 1978. Avian nest dispersion and fledging success in field-forest ecotones. Ecology 59:871-883. Gillihan, SW. and T. VerCauteren. 2015. Pocket Guide to Prairie Birds. Brighton, CO: Bird Conservancy of the Rockies. 91 p. Gniadek, S. 1983. Southwest Glendive Wildlife Baseline Inventory. Miles City, Mont: Bureau of Land Management, Miles City District Office. 56 pp with appendices. Goodell, J. 2012. Morse Land Company Breeding Bird Inventory And Analysis. High Desert Museum. Bend, OR. 42 pp + Appendices. Hays, R., R.L. Eng, and C.V. Davis (preparers). 1984. A list of Montana birds. Helena, MT: MT Dept. of Fish, Wildlife & Parks. Hejl, S.J. 1994. Human-induced changes in bird populations in coniferous forests in western North America during the past 100 years. Studies in Avian Biology 15:232-246. Hejl, S.J., R.L. Hutto, C.R. Preston, and D.M. Finch. 1995. The effects of silvicultural treatments on forest birds in the Rocky Mountains. pp. 220-244 In: T.E. Martin and D.M. Finch (eds). Ecology and Management of Neotropical Migratory Birds. New York, NY: Oxford Univ. Press. 489 p. Henderson, S. 1997. Effects of fire on avian distributions and patterns of abundance over two vegetation types in southwest Montana : implications for managing fire for biodiversity. M.Sc. Thesis. Bozeman, MT: Montana State University. 95 p. Hendricks, P, S. Lenard, and C. Currier. 2012. Grassland Bird Surveys in North Valley County and Northwest Phillips County, Montana: 2011 Summary. Report to the USDI Bureau of Land Management. Montana Natural Heritage Program. Helena, MT. 7pp. Hendricks, P. 2000. Roadside bird counts on BLM lands in Petroleum and Fergus Counties, Montana. Montana Natural Heritage Program, Helena, MT. 57pp. Hendricks, P., G.M. Kudray, S. Lenard, and B.A. Maxell. 2007. A Multi-Scale Analysis Linking Prairie Breeding Birds to Site and Landscape Factors Including USGS GAP Data. Helena, Mont: Montana Natural Heritage Program. Hendricks, P., S. Lenard, D.M. Stagliano, and B.A. Maxell. 2013. Baseline nongame wildlife surveys on the Fort Peck Indian Reservation. Report to the Assiniboine and Sioux Tribes of the Fort Peck Indian Reservation. Montana Natural Heritage Program, Helena, MT. 83 p. Herbert, J.T. 1977. An inventory of the bird population within the Sarpy Creek drainage, southeastern Montana. M.Sc. Thesis. Bozeman, MT: Montana State University. 81 p. Hoffmann, R.S. 1960. Summer birds of the Little Belt Mountains, Montana. Missoula, MT: Occasional Papers of Montana State University No. 1. 18 p. Hutto, R. L., and J. S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service. U.S. Forest Service General Technical Report RMRS-GTR-32, Ogden, Utah. Johnsgard, P.A. 1979. Birds of the Great Plains: breeding species and their distribution. University of Nebraska Press, Lincoln. 539 pp. Johnsgard, P.A. 1992. Birds of the Rocky Mountains with particular reference to national parks in the northern Rocky Mountain region. Lincoln: University of Nebraska Press. xi + 504 pp. Joslin, Gayle, and Heidi B. Youmans. 1999. Effects of recreation on Rocky Mountain wildlife: a review for Montana. [Montana]: Montana Chapter of the Wildlife Society. Kantrud, H.A. 1982. Maps of distribution and abundance of selected species of birds on uncultivated native upland grasslands and shrubsteppe in the northern Great Plains. U.S. Dept. Int., Fish and Wildl. Serv. FWS/OBS-82/31. 31 p. Knopf, F.L. 1986. Changing landscapes and the cosmopolitism of the eastern Colorado avifauna. Wildlife Society Bulletin 14(2):132-142. Knopf, F.L., J.A. Sedgwick, and R.W. Cannon. 1988. Guild structure of a riparian avifauna relative to seasonal cattle grazing. J. Wildl. Manage. 52(2):280-290. Land & Water Consulting, Inc., Missoula, MT., 2002, Montana Dept. of Transportation Wetland Mitigation Monitoring Report, Year 2001: Browns Gulch, Rocker, Montana. Proj. No. 130091.012. July 2002. In 2001 Wetland Mitigation Monitoring Reports, Vol. I. Land & Water Consulting, Inc., Missoula, MT., 2002, Montana Dept. of Transportation Wetland Mitigation Monitoring Report, Year 2002: Browns Gulch, Rocker, Montana. Proj. No. 130091.012. February 2003. In 2002 Wetland Mitigation Monitoring Reports, Vol. I. Lenard, S. 2006. Birds of Blaine County, Riparian Point Count Surveys 2005. Report to the Bureau of LandManagement, Havre Field Station, Havre, Montana. Montana Natural Heritage Program, Helena, MT. 16pp.plus appendices. Lenard, S. and P. Hendricks. 2005. Birds of selected grassland and riparian plots along the Rocky Mountain Front. Montana Natural Heritage Program for US Fish and Wildlife Service and The Nature Conservancy. 17pp + maps. Lenard, S., Compiler. 2005. Surveys for Animal Species of Concern in Sage and Grassland Landscapes in Montana. An unpublished report to the Montana Department of Fish, Wildlife & Parks, State Wildlife Grants Program. Montana Natural Heritage Program, Helena, Montana. 63pp. Lenard, S., J. Carlson, J. Ellis, C. Jones, and C. Tilly. 2003. P. D. Skaar's Montana bird distribution, 6th edition. Montana Audubon, Helena, MT. 144 pp. Lowther, P.E. 1993. Brown-headed Cowbird ( Molothrus ater). Species Account Number 047. The Birds of North America Online (A. Poole, Ed.). Ithaca, NY: Cornell Laboratory of Ornithology; Retrieved 3/25/2008 from The Birds of North America Online database Lyons, T.P., J.R. Miller, D.M. Debinski, and D.M. Engle. 2014. Predator identity influences the effect of habitat management on nest predation. Ecological Applications 25(6): 1596-1605. Matthews, W.L. 1980a. Wibaux-Beach comparison study: Sydney, Glendive and Plevna Study Areas. Bureau of Land Management, Miles City, MT. 50 p. Matthews, W.L. 1981. Broadus-Pumpkin Creek baseline inventory - wildlife. Bureau of Land Management, Miles City, MT. 83 p. Maxell, B.A. 2016. Flammulated Owl surveys on the Big Timber, Bozeman, Gardiner and Livingston Ranger Districts of the Custer Gallatin National Forest: 2013. Report to Custer Gallatin National Forest. Montana Natural Heritage Program. Helena, MT. 27pp + appendices. Maxell, B.A. 2016. Northern Goshawk surveys on the Beartooth, Ashland, and Sioux Districts of the Custer-Gallatin National Forest: 2012-2014. Montana Natural Heritage Program. Helena, MT. 114pp. Mayfield, H.F. 1965. The brown-headed cowbird, with old and new hosts. Living Bird 4: 13-28. McWethy, D.B. 2007. Bird response to landscape and pattern disturbance across productivity gradients in forests of the Pacific Northwest. Ph.D. Dissertation. Bozeman, MT: Montana State University. 184 p. Montana Bird Distribution Committee. 2012. P.D. Skaar's Montana bird distribution. 7th Edition. Montana Audubon, Helena, Montana. 208 pp. + foldout map. Mosher, B.A. 2011. Avian community response to a mountain beetle epidemic. M.Sc. Thesis. Bozeman, MT: Montana State University. 55 p. MT Fish, Wildlife & Parks. No date. Blackfoot-Clearwater Wildlife Management Area checklist. Newlon, K.R. 2005. Demography of Lewis's Woodpecker, breeding bird densities, and riparian Aspen integrity in a grazed landscape. M.Sc. Thesis. Bozeman, MT: Montana State University. 101 p. Oechsli, L.M. 2000. Ex-urban development in the Rocky Mountain West: consequences for native vegetation, wildlife diversity, and land-use planning in Big Sky, Montana. M.Sc. Thesis. Montana State University, Bozeman. 73 p. Pavlacky Jr., D.C., et al. 2021. Landscape-scale conservation mitigates the biodiversity loss of grassland birds. Ecological Applications e2548. 17 p. Pitkin, P. and L. Quattrini. 2017. Pocket Guide to Sagebrush Birds. Bird Conservancy of the Rockies and Point Blue Conservation Science. 68 p. Ralph, J.C., J.R. Sauer, and S. Droege. 1995. Monitoring bird populations by point counts. Gen. Tech. Rep. PSW-GTR-149. Albany, CA: USDA Pacific Southwest Research Station. 181 p. Richmond, C.W. and F.H. Knowlton. 1894. Birds of south-central Montana. Auk 11:298-308. Rogers, R.R and A. Rogers. 1995. A survey of nesting ferruginous hawks (Buteo regalis) on public lands in Petroleum and Fergus counties, Montana. Prepared for the USDI Bureau of Land Management, Judith Resource Area. 17 p. 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. Rundquist, V.M. 1973. Avian ecology on stock ponds in two vegetational types in north-central Montana. Ph.D. Dissertation. Bozeman, MT: Montana State University. 112 p. Sater, S. 2022. The insects of Sevenmile Creek, a pictorial guide to their diversity and ecology. Undergraduate Thesis. Helena, MT: Carroll College. 242 p. Saunders, A.A. 1914. The birds of Teton and northern Lewis & Clark counties, Montana. Condor 16:124-144. Shaffer, J.A., L.D. Igl, and D.H. Johnson. 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Sparks, J.M.Stenger, J.A. Rehm-Lorber, M.F. McLaren, F. Cardone, J.J. Birek and D.J. Hanni. 2011. Integrated monitoring of bird conservation regions (IMBCR): 2010 Annual Report. Brighton, CO: Rocky Mountain Bird Observatory. 387 p. Web Search Engines for Articles on "Brown-headed Cowbird"
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