Parasites With Wings

These are two female Brown-headed Cowbirds.

The Brown-headed Cowbird is a brood parasite species which lays its eggs in nests of other birds and leaves them for the host bird to raise.

Because cowbird eggs hatch a few days before those of their hosts, the larger cowbird chick is able to push out the eggs and chicks of the host bird, thereby winning all the food resources for itself.

The destructive capacity of the Brown-headed Cowbird is hard to overestimate: a single female can destroy the clutches of 20 or more song birds in a single season.

In pre-Columbian times, cowbirds were resident in the Great Plains, and rare or non-existent on the East Coast. Today, however, the tree cover provided by shelterbelts along the edges of farm fields provides a near-perfect habitat for these destructive birds.