By Corey Lewis, Humane Wildlife Control
The adult females do not make or keep a nest. She lays her eggs among eggs already in nests built by other birds. Cowbird babies are larger and faster growing than the host species, and so out-compete the host chicks for food. As the Cowbird chick gets even bigger, it evicts the other babies who die on the ground. The Cowbird gets fed and raised by the unsuspecting host parents who seemingly have know clue whats going on.
Cowbirds developed this strategy by following the great herds of bison on the plains. Always moving around, they eventually developed this brood parasitizing behaviour.
They eventually hooked up with people herding cattle and sheep, moving into more agricultural areas, but never re-learned how to raise a family.
Cowbirds eat the bugs stirred up by the roaming bison or cattle, hence the name “cowbird”.