Centuries ago, this bird probably followed the 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. Cowbirds lay their eggs in nests of other birds, leaving the "host" to raise the young.
The Brown-headed Cowbird favors open or semi-open country at all seasons. In winter it often concentrates in farmland, pastures or cattle feedlots, when foraging is easy.
Mostly seeds and insects. Seeds, including those of grasses, weeds and waste grain, make up about half of their diet in summer and more than 90% in winter. The rest of their diet is mostly insects. Often associated with cattle or horses in pastures, catching the insects flushed from the grass by the grazing animals.
A brood parasite, its eggs and young being cared for by other bird species. It doesn't build a nest, but lays it eggs in nests of other birds.
Whitish with brown and gray spots. Females may lay nearly an egg per day for several weeks, up to 40 in a season. Female often removes an egg from the "host" nest before laying one of her own. Known to have laid eggs in nests of over 220 species of birds, and over 140 are known to have raised young Cowbirds.
The Cowbird nestlings are fed by the "host" parents. They develop rapidly and leave the nest after 10-11 days.