Photo: Rob & Ann Simpson/Vireo

Brown-headed Cowbird

Molothrus ater

Centuries ago this bird probably followed bison herds on the Great Plains, feeding on insects flushed from the grass by the grazers. Today it follows cattle, and occurs abundantly from coast to coast. Its spread has represented bad news for other songbirds: Cowbirds lay their eggs in nests of other birds. Heavy parasitism by cowbirds has pushed some species to the status of "endangered" and has probably hurt populations of some others.
Conservation status Undoubtedly far more abundant and widespread today than it was originally, and having a negative impact on other species. Surveys suggest slight declines in total numbers in recent decades.
Family Blackbirds and Orioles
Habitat Farms, fields, prairies, wood edges, river groves. Favors open or semi-open country at all seasons. In winter often concentrates in farmland, pastures, or cattle feedlots, where foraging is easy. More widespread in breeding season, in grassland, brushy country, forest edges, even desert, but tends to avoid dense unbroken forest.
Centuries ago this bird probably followed bison herds on the Great Plains, feeding on insects flushed from the grass by the grazers. Today it follows cattle, and occurs abundantly from coast to coast. Its spread has represented bad news for other songbirds: Cowbirds lay their eggs in nests of other birds. Heavy parasitism by cowbirds has pushed some species to the status of "endangered" and has probably hurt populations of some others.
Photo Gallery
Feeding Behavior

Forages mostly by walking on the ground. Often associates with cattle or horses in pastures, catching the insects flushed from the grass by the grazing animals. Originally, was closely associated with bison herds on the Great Plains.


Eggs

Whitish with brown and gray spots concentrated at larger end. Female may lay nearly one egg per day for several weeks, up to 40 in a season, exceptionally 70 or more. Female often removes an egg from "host" nest before laying one of her own. Known to have laid eggs in nests of over 220 species of birds, and over 140 of those are known to have raised young cowbirds. Young: Fed by "host" parents. Develop rapidly, and leave nest usually after 10-11 days.


Young

Fed by "host" parents. Develop rapidly, and leave nest usually after 10-11 days.

Diet

Mostly seeds and insects. Seeds (including those of grasses, weeds, and waste grain) make up about half of diet in summer and more than 90% in winter. Rest of diet is mostly insects, especially grasshoppers, beetles, and caterpillars, plus many others, also spiders and millipedes.


Nesting

A brood parasite, its eggs and young being cared for by other bird species. In breeding season, male displays by fluffing up body feathers, partly spreading wings and tail, and bowing deeply while singing. Groups of males sometimes perch together, singing and displaying. Nest: No nest built; eggs laid in nests of other birds.

Text © Kenn Kaufman, adapted from
Lives of North American Birds

Illustration © David Allen Sibley.
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Migration

Present all year in many southern areas. Very widespread in nesting season, localized at other times. May begin to depart from nesting areas by August or even July.

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Migration

Present all year in many southern areas. Very widespread in nesting season, localized at other times. May begin to depart from nesting areas by August or even July.

  • All Seasons - Common
  • All Seasons - Uncommon
  • Breeding - Common
  • Breeding - Uncommon
  • Winter - Common
  • Winter - Uncommon
  • Migration - Common
  • Migration - Uncommon
Songs and Calls
Squeaky gurgle. Call is check or a rattle.