Brown-headed cowbirds are members of the blackbird family with short, conical bills and long, pointed wings. Males have an iridescent black bodies and brown heads. Females are slightly smaller than the males and are uniformly gray. The upperwing and underwing coverts of adult males are black while those of younger birds show a brown or brown-gray wash. The primary flight feathers of adult males are also black while those of females are more of a brown-gray. They grow to a length of six to eight inches with a wingspread of 11 to14 inches and weigh an average of one to 1.75 ounces. Their song is a bubbly glug-glug-glee, their call is a chuck, and their flight note is a high whistle. Brown-headed cowbirds are also known as: brown-headed blackbird, brown-headed oriole, buffalo bird, cow blackbird, cow bunting, cow-pen bird, cuckold and lazy bird. Range:
Originally birds of the Great Plains, the brown-headed cowbird has spread from coast to coast. They are found from southeastern Alaska across to New Brunswick and south to central Mexico. They are a short-distance migrant within North America, and winters are spent throughout the southern portion of their breeding range. Brown-headed cowbirds are common throughout Colorado. Distribution gaps occur in areas of extensive cropland, desert shrub and the backbones of high mountain ranges.
Habitat: Brown-headed cowbirds prefer habitats where low or scattered trees are interspersed with grassland vegetation. Originally, they occupied open grasslands and followed bison herds where they fed on insects stirred up by the bison’s feet. However, due to widespread domestic livestock grazing they have expanded their range. Today, they are found in open coniferous and deciduous woodlands, forest edges, brushy thickets, agricultural land and even some suburban areas.
Diet: Brown-headed cowbirds often forage on the ground away from vegetation. Their diet consists mainly of seeds (roughly 75 percent) and arthropods such as grasshoppers and beetles. Sometimes they hawk for food, searching for slow flying insects.
Reproduction: The brown-headed cowbird is a brood parasite. They do not make a nest of their own, instead, the female lays her eggs in nests of other bird species. From mid-May until late July, she may lay one egg a day parasitizing many nests. A female can lay between 40 and 80 eggs in one season. In some cases, the cowbird removes one or more of the host bird’s eggs. The cowbird’s egg hatches quickly (11 days) and usually a day or two before the host’s eggs. Most host parents will raise the cowbird chick as their own. Rapid growth allows the cowbird chick to out-compete the host’s chicks for food and space in the nest. The result is that the host’s chicks usually perish. Cowbirds are known to use 144 different host species, from the small creeper to larger meadowlark. Some birds with a long history of exposure to cowbirds recognize the foreign egg and abandon the nest, and/or act aggressively to cowbirds near their nesting territory.
For more information, see the Natural Diversity Information Source species profile.