While taking a leisurely walk down the San Gabrielino Trail in the Angeles Forest one might come across a variety of native wildlife. There are sunny patches of light pinks and whites from the freshly blooming California Buckwheat and the soothing sound of a watery creek bed with slender green arroyo willow leaves rustling in the wind along this trail.
A particular bird catches your eye as it briskly flies from one tree branch to another. It has a brown feathered body with a small black beak, and it appears to be nesting on one of the branches of an Arroyo Willow tree. You take a closer look, and you soon realize that nest does not belong to that bird; it actually belongs to a Least Bell’s Vireo, an endangered species who thrives off of riparian habitat in the Los Angeles basin. The imposter is a Brown-headed Cowbird, and it is known as a brood parasite: a bird that lays its eggs in the nest of others.
Oddly enough, this bird is a protected native species, even though it is hurting other native bird populations. With a state permit, agencies can set up traps to capture and remove cowbirds from certain areas such as the Upper Buck Gully in the Newport Beach area. Biologists and conservancies have been keeping an eye on these native opportunists and how they behave. It turns out that their method of survival is very successful for them since they used to mix with bison herds when they roamed across the Midwest.
Today, the Brown-headed Cowbird is often seen near cows grabbing a bite of tasty insects off of their backs. Since bison herds always migrate, these birds were unable to survive by building a stationary nest to incubate their eggs, then nurse their chicks for weeks on end until they are strong enough to survive on their own. That is why the Cowbird evolved its brood parasitism strategy, because it was the only way to ensure their species survival.