Sunday, January 4, 2009

The Cowbird; A Tribute

Over the past 4 months or so I've developed a keen interest in bird watching. Upon moving to our new residence in West Lafayette, Indiana, I was delighted to see that our rental house was equipped with a hopper-style bird feeder, which I began filling at once. Armed with my Golden Guide to Birds of North America and a pair of binoculars, I have spent weekend mornings searching for new species in our small but well-vegetated yard. Now, thirty species later, I can say that I'm surprised by the variety of birds that have come to call, everything from finches to woodpeckers to sparrows to nuthatches to hummingbirds to hawks. But today was the first day that I've sighted a brown-headed cowbird.

Cowbirds aren't the loveliest of birds, as the name cowbird may suggest, nor is it the most beloved, as the name cowbird may also suggest. Why then, when there are cedar waxwings and common flickers to fawn over, does the cowbird capture my imagination?

Because behaviorally, the cowbird is among the most fascinating. We don't commonly think of birds as parasites, but if ever there was an all-around a-hole of the bird kingdom, the cowbird is it. A cowbird, instead of building its own nest and sitting on its own eggs, will invade another bird's nest and lay an egg there. Sometimes the cowbird will actually remove one of the host bird's eggs to make room for her own. Check out this photo. Can you tell which of these eggs doesn't belong?

The cowbird doesn't stick around to care for its young, either. No, she instead lets the host bird incubate her egg and subsequently raise the baby bird. Even more amazingly, a cowbird typically hatches a day or two before the host eggs and a baby cowbird will pine more noisily for food from its foster parents. The result is often detrimental to the other chicks, who cannot compete. Interestingly, a cowbird, unlike other parasitic birds, does not kill its 'siblings.' Scientists believe that in joining a chorus of hungry chicks, parent birds will bring more food to the nest, which the aggressive cowbird will then hog. Subtle and villainous, even at birth.

And it gets even better. Cowbirds have been documented to have invaded the nest of 220 different species of bird. Yet very few are the cowbird eggs that result in a healthy offspring. Often, host parents reject the egg or the baby cowbird. But cowbirds lay eggs so frequently and are so promiscuous in their mating habits that the species thrives in spite of the low percentage of successfully raised chicks. And woe to those birds who do reject the cowbird egg, because female cowbirds are not totally disdainful of their progeny. Periodically during the incubation period a mother will check on her egg, and cowbirds have been known to ransack the nest of the host bird if she finds the egg missing.

Unattractive, gluttonous, greedy, manipulative, ruthless and even vengeful, the cowbird is the Nixon of the birding world. I thank the little bastard for brightening my day.


1 comment:

Kid Shay said...

It's good to see that the spirit of Nixon, if not the man, is alive and well in your backyard.