The Brown-headed Cowbird is known for its unusual reproductive strategy called brood parasitism. Instead of building their own nests, females lay eggs in the nests of other bird species—up to 30 per season. The host birds, often unaware, raise the cowbird chick, which typically hatches earlier and grows faster than the others, often at the expense of the host’s own young.
Cowbird chicks can be two to three times the size of their foster parents, making feeding and care especially demanding. However, not all host birds are fooled—some destroy the foreign egg or abandon the nest entirely.
This behavior evolved because cowbirds historically followed bison herds across the plains, leaving them no time to settle and raise young. As the bison disappeared and agriculture spread, cowbirds expanded their range eastward into regions like Ontario, adapting to new habitats while keeping their parenting-optional lifestyle.
The Brown-headed Cowbird is known for its unusual reproductive strategy called brood parasitism. Instead of building their own nests, females lay eggs in the nests of other bird species—up to 30 per season. The host birds, often unaware, raise the cowbird chick, which typically hatches earlier and grows faster than the others, often at the expense of the host’s own young.
Cowbird chicks can be two to three times the size of their foster parents, making feeding and care especially demanding. However, not all host birds are fooled—some destroy the foreign egg or abandon the nest entirely.
This behavior evolved because cowbirds historically followed bison herds across the plains, leaving them no time to settle and raise young. As the bison disappeared and agriculture spread, cowbirds expanded their range eastward into regions like Ontario, adapting to new habitats while keeping their parenting-optional lifestyle.