PHOTO OF THE WEEK: Brown-headed Cowbird

Do you notice anything wrong with this picture? I was walking to dinner yesterday (June 17th, 2014) on the campus of the University of Notre Dame in South Bend, Indiana when I happened upon this fascinating scene. A chipping sparrow (Spizella passerina) bounced up to a chirping, young icterid (blackbird family). As the young bird increased its excited begging, the sparrow dropped a morsel down its throat. Of course, by then I knew exactly what was going on. The brown-headed cowbird (Molothrus ater) is a parasite!
A female brown-headed cowbird can lay over 30 eggs a spring but most of these will never develop. While many eggs are rejected by the host birds, other young cowbirds are left to die after they hatch as the victim parents discover the truth about their youngster. Cowbirds don't always pick the right nest, either. If the host bird is a fruit eater, the baby cowbird can't get the protein it needs to develop and survive. Yes, life is hard as a cowbird. To help with this, cowbirds make life very difficult for bird families that won't "adopt" their babies. If an egg or young cowbird is rejected from a nest, the cowbird parent will terrorize the nest, often killing the natural young inside or destroying the nest altogether. In the case I photographed above, it appears as if the only surviving youngster in the family was the cowbird.
The bird gets its name from its previous way of life in the midwest and great plains; following the great herds of bison (Bison bison). Although the bison herds are largely dissipated, the cowbird has found living in suburban areas suitable. You've got to respect a bird that has adapted to a lifestyle among the causers of the disappearance of its previous way of life.
I had to wait about 15 minutes under the tree before the sparrow returned once again to feed the cowbird chick and I was able to get this photo. Although many people work against cowbirds to try to eradicate them, I appreciate the cowbird's way of life as a natural part of a cursed world. It's just like predation: it's not pretty, but it is a natural part of life (and death). And besides, the thinning of the species actually increases the amount of parasitism that takes place because cowbirds do not desert as many parasitized nests when populations are low (see reference below).

Reference:

Hall, Ackert. 2008. “Cowbird Removals Unexpectedly Increase Productivity.” Ecological Applications. 18(2):537–48. Retrieved June 18, 2014 from http://www.k-state.edu/bsanderc/2008ecolappl.pdf