Brown-headed Cowbird

Molothrus ater


Year-round Resident

Brown-headed Cowbirds are abundant year-round residents in the Washington metro area. During the winter, you sometimes can see flocks of hundreds of them feeding on the ground, often mixed with European Starlings. They are one of the least popular bird species in North America, because they are parasitic nesters. They do not build their own nest. Instead, the extremely fertile females lay eggs in the nests of other species. A female can lay three dozen eggs during a breeding season. Brown headed Cowbirds have laid their eggs in the nests of at least 220 species, and at least 140 species have raised cowbird chicks. Cowbirds usually choose host species who are smaller and whose eggs take longer to hatch.

Where to See Them in the Park

Cowbirds forage on the ground or in low vegetation. Because not many bird species nest at Monticello, few cowbirds are seen at the park during the spring.

Physical Description


Brown-headed Cowbird Male
Male - Photo by Ashley Bradford

Male cowbirds have a dark iridescent body and a dull brown head. The bill is surprisingly large and stout. Cowbirds typically forage on the ground for seeds and insects.

Brown-headed Cowbirds
Foraging cowbirds, males and females - Photo by Ashley Bradford

Brown-headed Cowbird Female
A female cowbird with grass seeds - Photo by Ashley Bradford

Brown-headed Cowbird Females
Females - Photo by William Higgins

Female cowbirds can be difficult to identify. They are almost entirely brown, with no characteristics standing out. The stout bill can be an important fieldmark. A female often mates with numerous males during the breeding season.

Brown-headed Cowbird Male and Female
A male cowbird displaying for a female - Photo by Ashley Bradford

Brown-headed Cowbird Male and Female
A male cowbird displaying for a female - Photo by Ashley Bradford

Vocalizations

The song of Brown-headed Cowbirds is short, thin, bubbly, and ascending. Cowbirds also deliver a characteristic sputter. They can be quite vocal, except when they are surreptitiously trying to deposit their eggs into the nests of other species.

Hear the vocalizations of the Brown-headed Cowbird.

Notes

Outside of the United States, the best known avian brood parasite is the Common Cuckoo, who is found in Eurasia and Africa. The word "cuckold" is derived from the behavior of the cuckoo. A human husband is said to be cuckolded if his wife becomes sexually involved with another man. However, the activity for which cuckoos and cowbirds are best known does not involve cuckoldry. It is more akin to leaving a fetus on a doorstep. Cowbirds are not always careful about the hosts they choose; they have left eggs in hawk nests. They sometimes parasitize House Finches, but because the finches feed their chicks mostly seeds and other plant material rather than insects, the baby cowbirds tend not to survive. The behavior of Brown-headed Cowbirds has implications for many bird species, and it has been studied and written about by Professor David White of the University of Pennsylvania and others.

Origin of Names

Common Names: Brown-headed from the plumage. Cowbird because they often forage near cattle in agricultural areas.
Genus Name: Molothrus is Greek for "struggle to sire".
Species Name: Ater means "dark", from the plumage.

Brown-headed Cowbird video footage

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