3 September 2025

The breeding season is over for brown-headed cowbirds in Pittsburgh. The adults courted constantly while the females were fertile but egg-laying stopped in mid-July. By now all the youngsters have fledged and left their hosts to join flocks of cowbirds. These youngsters were raised by another species so how do they know what flocks to join? A new study found out their parents have nothing to do with it.

Parental neglect starts early. Female brown-headed cowbirds (Molothrus ater) are brood parasites that lay their eggs in the nests of smaller birds.  Each cowbird chick is raised, not by its own mother, but by foster parents of another species. Initially the cowbird female lurks near the foster nest to make sure her own egg survives and will sometimes destroy the host’s eggs if her own egg disappears. But after that she’s too busy laying up to 40 eggs per season.

If the biological parents don’t care for it, why doesn’t the young cowbird stay with its host species?

Unlike most birds, a young brood parasite doesn’t get attached to its host parents. You can see this if you rear cowbirds by hand, said Mark Hauber, a comparative psychologist at CUNY Graduate Center in New York: “They start hating you at some point.” If a cowbird imprinted on a family of yellow warblers, say, and sought out warblers’ company as an adult, it would never find a mate and reproduce.

— New York Times: How a Parasitic Bird With No Parents Learns What Species It Is

Early studies on how the youngsters discover their own species found that young cowbirds are attracted to the chattering calls of adult females, prefer to associate with birds whose plumage matches their own (immatures and females look similar), and many even hang out with their mothers.

However, the new study published in ScienceDirect in August conducted DNA tests on groups of immature cowbirds and adults captured together and found that the youngsters always hung out with females but they were never related to them.

Somehow, Chamberlain says, they bump into adult cowbirds and start hanging around them and learning how to behave. But the clock is ticking: By the end of the summer, the juveniles and adults will migrate south. “They have a short time period in which they need to learn these things,” Mr. Chamberlain said.”

— New York Times: How a Parasitic Bird With No Parents Learns What Species It Is

Groups of women teach the young. It takes a village to raise a cowbird.