The Brown-headed Cowbird, Molothrus ater, is a small bird of the Icteridae family. They are residents to open and semi-open country across most of North America. They are permanent residents in the southern parts of their range. Northern birds migrate to the southern United States and Mexico. At one time, the Brown-headed Cowbird followed the bison herds across the prairies. Their numbers expanded with the clearing of forested areas and the introduction of new grazing animals by settlers across North America.
Adults have a short finch-like bill and dark eyes. The adult male is mainly iridescent black with a brown head. The adult female is gray with a pale throat and fine streaking on the under parts. Brown-headed Cowbirds often travel in flocks, sometimes mixed with Red-winged Blackbirds or European Starlings.
These birds forage on the ground, often following grazing animals such as horses and cows to catch insects stirred up by the larger animals. They mainly eat seeds and insects. They are also commonly seen at suburban birdfeeders.
The Brown-headed Cowbird, like other cowbirds, is a parasitic bird. It lays its eggs in the nests of other small passerine birds. The young cowbird is fed by the host parents at the expense of their own young. Brown-headed Cowbirds can lay as many as 36 eggs in a season. Over 140 different species of birds are known to have raised young cowbirds. Host parents may sometimes notice the cowbird egg and either destroy it or build a new nest over the original. Sometimes the hatched young is expelled from the nest as well.