Why Does the Cowbird Lay Its Eggs in the Nests of Other Birds? Cowbirds do not raise their own young. They lay their eggs in the nests of other birds for the foster parents to raise. The female cowbird chooses a nest that belongs to some small bird, and usually lays only one egg in it while the other birds are away.
Then she flies off and does not return. The foster parents hatch the egg and feed the young cowbird. They do not seem to realize they are raising an outsider.
When the cowbird grows up, it feeds on insects that fly up in front of cattle’s feet. This is how the cowbird got its unusual name.
Today there are two native cowbird species in North America, the Bronzed Cowbird of the Southwest and the Brown-headed Cowbird common in most of the United States and Canada.
Both species of cowbirds do not raise their own young and lay their eggs in the nests of other birds, which is to say that both maintain the parasitic tradition of their ancestors, much to the dismay of bird lovers and conservationists.
At least 100 species of birds are known victims of the cowbird’s sneaky behavior. 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.
Content for this question contributed by Jennifer Helton, resident of Chula Vista, California, USA