By Johnny Sain
Brown-headed cowbirds, like so many other things in life, are a contradiction. The males are striking, with chocolate brown heads and iridescent midnight blue bodies. The males also have a peculiar call. A liquid sounding “gug-a-link” that is both cheery and unmistakable. You can listen to that call and watch the male strut like a miniature turkey in the video attached to this post.
But brown-headed cowbirds also have a dark side. They are brood parasites, like Eurasian cuckoos and to a lesser extent American cuckoos. Brown-headed cowbirds have been know to parasitize over 220 different species of birds.
Female brown-headed cowbirds watch and wait for other bird species that are actively laying eggs and sneak in as the host is away to lay a single egg in the nest. She often destroys a host’s egg beforehand to make room for her own. Cowbird eggs usually require a shorter incubation than the host’s eggs and the cowbird matures quicker than its nest mates, which means the young cowbird outcompetes the host’s hatchlings for parental feeding. As the cowbird grows larger it often pushes other hatchlings out of the nest. And in a stunning display of the drive to nurture, the host will continue to feed the young cowbird even as the cowbird grows to double or more the size of its host parents. As if more evidence of sinister intentions is needed, brown-headed cowbirds have been known to destroy the nests of host bird parents that reject the cowbird egg or build another nest on top of it.
Of course cowbirds are not evil. It’s just another fantastic display of adaptation. Back when North America was still an untamed land, and great herds of bison roamed the continent, brown-headed cowbirds followed those herds. Since cowbird parents couldn’t hang around to rear their offspring, a parasitic brooding behavior worked for the cowbirds. Now the herds of bison are gone. The land is fenced and crisscrossed with roads, and brown-headed cowbirds typically hang out in one location during their summer stay in the U.S. The decline of some cowbird host species has been blamed on this shift in movement patterns. But while the cowbirds may be guilty of what some would call heinous behavior, habitat destruction is the most likely cause of specific species decline.
While the destruction of forests has hurt many species of birds, brown-headed cowbirds have thrived under the creation of more open areas. They can be found just about anywhere there is pasture or open land and they love to hang around livestock. Brown-headed cowbirds eat insects and various seeds. They aren’t good at perching on wire feeders, but will flock to areas of spilled seed and clean up anything falling from the feeder.
Brown-headed cowbird behavior might seem disturbing to our human ideas of morality, but they are perfectly adapted to life in wild pre-European settlement America.