Brown-headed cowbirds spend the summer in Decorah. Grass and weed seeds make up about 75% of their diet. The other 25% consists of insects, snail shells, and an occasional egg. Cowbirds are brood parasites. Instead of building their own nests, they lay eggs in the nests of other birds of more than 220 species of birds. Their eggs need 10-12 days of incubation and nestlings stay in the nest for 8-13 days. To learn more, visit Cornell’s website.
So how does a Brown-headed Cowbird, raised by parents of a different species, learn to sing the correct song? The “chatter call” of an adult cowbird triggers something in a fledgling’s brain that guides it to recognize its own species, even though cowbirds are fostered by as many as 220 different species! (https://www.birdnote.org/show/cowbird-song-and-password)
Genetic analyses show that most individual females specialize in a host species. In much the same way that birds can imprint on humans, perhaps they were raised by that species and see them as appropriate parents for their young.