Least Concern


Brown-headed Cowbird

Molothrus ater

The Brown-headed Cowbird is a small brood parasitic bird of temperate to subtropical North America. They are permanent residents in the southern parts of their range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat about March OR April.

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 grey with a pale throat and fine streaking on the underparts.

They occur in open or semi-open country and often travel in flocks, sometimes mixed with Red-winged Blackbirds and Bobolinks, as well as Common Grackle 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.

This bird is a brood parasite. It lays its eggs in the nests of other small passerines, particularly those that build cup-like nests. The young cowbird is fed by the host parents at the expense of their own young. Brown-headed Cowbird females can lay 36 eggs in a season.

Host parents may sometimes easily notice the cowbird egg, to which different host species react in different ways. The House Finch feeds its young a vegetarian diet, which is unsuitable for young Brown-headed Cowbirds. Although the Brown-headed Cowbird eggs laid in a House Finch nest will hatch, almost none survive to fledge.

Brown-headed Cowbirds periodically check on their eggs and young after they have deposited them. Removal of the parasitic egg may trigger a retaliatory reaction. Cowbird destroyes the hosts nests if cowbird eggs are rejected which force the hosts to build new ones.


Regional Names
  • French:
    Vacher à tête brune
  • Spanish:
    tordo cabecicafé, tordo negro, tordo negro común, tordo cabeza marrón, tordo cabeza café, tordo cuco, vaquero cabecicafé, vaquero de cabeza castaña o boyero negro
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Molothrus ater

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