The interesting history of the cowbird

Wild Connections

By The Masked Biologist

Invariably whenever I visit my mother’s house, she has some kind of wildlife question for me. Last time I was there, she mentioned that she had seen a bird at her feeder that was new to her, and had hoped I could identify it. Even though I am a fan of birds, and I read, write and study about them often, identification by song or description does not come easy to me. She had not taken a photo, but I told her I would try anyway. The bird was black with a brownish head. I smiled and said “brown-headed cowbird.” Mom thought I was making fun of her; when she visited me at my work station in the Great Plains, she had asked me what the black birds with the yellow heads were. I told her that they were yellow-headed blackbirds, and she seemed disappointed that the name was so easy. In the case of the brown-headed cowbird, it obviously has a brown head but where does the cowbird part of the name come from? Gray catbirds are so named because they make a sound like kitten mewing, but cowbirds do not moo. Cowbirds are originally birds of the plains and prairies, likely travelling with herds of buffalo or cattle. As settlers cleared forests, planted crops, started raising livestock and built towns, these birds expanded their territory and are now widespread across much of the continent.

Mom was excited to see a new kind of bird at her feeder, but was disappointed when I started telling her how wicked and villainous those birds are. Frankly, in my circles, few birds have a worse reputation than Brown-headed Cowbirds. The reason is their unique approach to nesting, if you can call it that. In fact, this species never builds a nest. Rather, the female cowbird finds an unattended nest with eggs in it, just about any nest, lays an egg and flies away. One female can lay three dozen eggs or more in a year! Unfortunately, these cowbirds typically hatch earlier than the other eggs laid in the nest, leading the unsuspecting parent to stop incubating her own eggs and start feeding the cowbird. This is an extremely effective reproductive method requiring almost no effort; the male does not need to defend a territory or start a nest; the female does not need to finish a nest or incubate eggs; neither parent needs to feed or protect the young. This could well be an adaptation to their somewhat nomadic roots; if they traveled with herds of buffalo it would have been difficult to stay in one spot long enough to raise a brood.

Unfortunately this has a devastating effect on some species of nesting songbirds that have not adapted strategies for dealing with cowbird egg intrusion. Honestly I used to think no bird was equipped to deal with their nest parasitism, as it is called. However, birds of the open grasslands and overlapping territories have developed impressive adaptations. Red-winged blackbirds, for example, will put a new bottom in their nest overtop the offending egg and lay more of their own eggs. American Robins lay beautiful blue eggs, which apparently helps them identify offending ova interlopers and avoid hatching them.

Can we malign this bird for capitalizing on centuries of survival adaptation? This bird traveled the Great Plains with the buffalo long before our ancestors decided to call this place home. Given the change that humans have brought about to the landscape of this country, we have opened the door for birds like these to expand and thrive. Mom can go ahead and be happy that she has this bird at her feeder. Any bird that has figured out how to lay 36 eggs a year without building a nest, and never has to do any work to raise her young deserves at least a little credit and admiration for ingenuity.

The Masked Biologist earned a bachelor of science degree from a university with a highly regarded wildlife biology program. He has work for natural resource agencies from the Rocky Mountains, across the Great Plains and into the Midwest, which provided opportunities to work with a variety of common and rare fish, plant and wildlife species. Follow The Masked Biologist on Facebook.