Jan 2, 2008

Lifebird #26 - Another Unpopular Bird

The Brown-headed Cowbird is another species we love to hate dislike. It’s not a non-native or introduced species, at least in the normal sense. But it really shouldn’t be found in my yard. Cowbirds evolved to follow bison around the great plains of North American (bisonbirds?), and do not penetrate more than a few hundred yards into wooded areas. But because of the fragmentation of forests and the loss of their preferred habitat, they are now found in locations where they were formerly absent. My yard is one example.

Brown-headed Cowbirds are very successful brood parasites. This was a key adaptation that allowed them to follow bison herds around the plains. Cowbirds lay their eggs in the nests of other species, and leave the raising of their young to their unwitting foster parents. One of my first cowbirds was a juvenile being fed by its Northern Cardinal “parents” at our feeders. Joann and I were very inexperienced birders at the time, and didn’t know what to make of a pair of cardinals feeding a big “sparrow” (a juvenile cowbird looks something like a large sparrow or a female grosbeak to me). With the help of the Internet and our copy of The Sibley Guide to Birds, we figured it out.

We don’t see huge numbers of cowbirds in our yard, but we do seem to see them everywhere else (their numbers are increasing), and we occasionally see Northern Cardinals and Chipping Sparrows feeding big, ugly foster children from our feeders. I took the photo of this male cowbird in our yard; he was probably standing guard as his mate deposited an egg in the nest of a unsuspecting songbird. The cretins!