Brown-headed cowbird • Molothrus ater
Male (dark plumage) and female (light plumage) brown-headed cowbirds on Calvert Island. Photos by Kim Wetten (left) and Sharlene James (right) with the VIU Bird Banding Project.
Identification
The brown-headed cowbird gets its name from the male's plumage, as its brown head contrasts with the metallic green-black plumage of the rest of its body. In poor lighting the iridescence may not be visible, or the head may appear black. The female's plumage is plain greyish-brown and lighter on the head and underparts, with some faint streaking on her belly. Juveniles are similar to females, but with more streaking on the belly and breast. The brown-headed cowbird has black eyes and a black, thick, cone-shaped bill.
Habitat & Range
The brown-headed cowbird can be found in open and semi-open habitats year-round, such as farmlands, fields, prairies, the edges of woodlands, thickets, and suburbs. It often is found in association with cattle and horses in pastures, eating insects disturbed by grazing. This bird is abundant throughout most of North America, and is found year-round in much of the southern and coastal parts of the continent (click here for a range map). It is present on the Central Coast during the spring breeding months. Find out more about this species' occurrence in BC using the BC Breeding Bird Atlas.
Similar Species
If the contrast between the male's brown head and metallic body is not visible, this blackbird may be confused for others of its family; on the BC coast the most likely lookalike is the Brewer's blackbird, which has a thinner bill, a longer tail, and is somewhat larger. The male has yellow eyes and a greenish sheen to the head and neck, while the female Brewer's blackbird has a darker throat than the female cowbird.
Intriguing Info
Instead of building its own nests, the brown-headed cowbird lays its eggs in the nests of other bird species; these eggs are hatched and raised by the host birds alongside their own (this is called obligate brood parasitism). Throughout its range it has been recorded laying eggs in the nests of over 200 species. Eggs of the host species may be removed by the female cowbird to make room for her egg, or by the young cowbirds once they hatch. Young develop quickly and are fed by the host parents. Some host species recognize and either remove the imposter eggs or build a new nest on top, while others accept the eggs as their own. Furthermore, evidence suggests some host species may recognize cowbird eggs but raise them anyway, as the cowbird parents may destroy the entire host nest if their eggs are rejected. Find out more about the brown-headed cowbird's brood parasitism on the NestWatch species page.
The brown-headed cowbird's range was once limited to central North America, but deforestation and forest fragmentation allowed it to substantially expand its range outward to most of the continent. This range expansion and population increase may be a contributing factor in the decline of some parasitized species.
iNaturalist
https://www.inaturalist.org/taxa/10373-Molothrus-ater
The brown-headed cowbird gets its name from the male's plumage, as its brown head contrasts with the metallic green-black plumage of the rest of its body. In poor lighting the iridescence may not be visible, or the head may appear black. The female's plumage is plain greyish-brown and lighter on the head and underparts, with some faint streaking on her belly. Juveniles are similar to females, but with more streaking on the belly and breast. The brown-headed cowbird has black eyes and a black, thick, cone-shaped bill.
Habitat & Range
The brown-headed cowbird can be found in open and semi-open habitats year-round, such as farmlands, fields, prairies, the edges of woodlands, thickets, and suburbs. It often is found in association with cattle and horses in pastures, eating insects disturbed by grazing. This bird is abundant throughout most of North America, and is found year-round in much of the southern and coastal parts of the continent (click here for a range map). It is present on the Central Coast during the spring breeding months. Find out more about this species' occurrence in BC using the BC Breeding Bird Atlas.
Similar Species
If the contrast between the male's brown head and metallic body is not visible, this blackbird may be confused for others of its family; on the BC coast the most likely lookalike is the Brewer's blackbird, which has a thinner bill, a longer tail, and is somewhat larger. The male has yellow eyes and a greenish sheen to the head and neck, while the female Brewer's blackbird has a darker throat than the female cowbird.
Intriguing Info
Instead of building its own nests, the brown-headed cowbird lays its eggs in the nests of other bird species; these eggs are hatched and raised by the host birds alongside their own (this is called obligate brood parasitism). Throughout its range it has been recorded laying eggs in the nests of over 200 species. Eggs of the host species may be removed by the female cowbird to make room for her egg, or by the young cowbirds once they hatch. Young develop quickly and are fed by the host parents. Some host species recognize and either remove the imposter eggs or build a new nest on top, while others accept the eggs as their own. Furthermore, evidence suggests some host species may recognize cowbird eggs but raise them anyway, as the cowbird parents may destroy the entire host nest if their eggs are rejected. Find out more about the brown-headed cowbird's brood parasitism on the NestWatch species page.
The brown-headed cowbird's range was once limited to central North America, but deforestation and forest fragmentation allowed it to substantially expand its range outward to most of the continent. This range expansion and population increase may be a contributing factor in the decline of some parasitized species.
iNaturalist
https://www.inaturalist.org/taxa/10373-Molothrus-ater
References
Brown-headed Cowbirds. NestWatch. Cornell Lab of Ornithology. Accessed 17/04/2018.
Dunn, J. L. and Alderfer, J. (Eds.). (2011). National Geographic Field Guide to the Birds of North America. (6th Ed.). Washington, D.C.: National Geographic Society. Pp. 448-449.
Brown-headed Cowbird Molothrus ater. Audubon Guide to North American Birds. Accessed 17/04/2018.
Brown-headed Cowbird Molothrus ater. The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology. Retrieved from the Birds of North America Online. Accessed 17/04/2018.
Authors and editors of page
Kelly Fretwell (2018).
Brown-headed Cowbirds. NestWatch. Cornell Lab of Ornithology. Accessed 17/04/2018.
Dunn, J. L. and Alderfer, J. (Eds.). (2011). National Geographic Field Guide to the Birds of North America. (6th Ed.). Washington, D.C.: National Geographic Society. Pp. 448-449.
Brown-headed Cowbird Molothrus ater. Audubon Guide to North American Birds. Accessed 17/04/2018.
Brown-headed Cowbird Molothrus ater. The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology. Retrieved from the Birds of North America Online. Accessed 17/04/2018.
Authors and editors of page
Kelly Fretwell (2018).