Atop Hawk Mountain, Pa., 2010

Atop Hawk Mountain, Pa., 2010
Photo by R.E. Berg-Andersson

Sunday, June 12, 2011

Love is Blind

I do not like cowbirds.

They are ugly birds. The male is black with a brown head that looks all black in dim light. The female looks like an oversized, gray house sparrow.

I do not like the female because she also has an ugly habit of dropping eggs in the nests of other birds. This is known as parasitizing.

The cowbird isn't the only bird to do this. Some cuckoos drop eggs into the nests of other cuckoos, for instance.

But parasitizing is the only way the cowbird can continue the species. Cowbirds don't build nests. Nor do they kick out other birds to take the nests, as owls do. It is not known why they must use the nests of songbirds.

That is why at this time of year, when I am hearing the first broods of chipping sparrows, starlings, robins and titmice making a ruckus as they chase their parents begging to be fed, I expect my annual sighting of some pair of adult birds being harried by a particularly large, aggressively hungry chick.

One year I was walking to the train and saw a pair of carolina wrens feverishly trying to fill the mouth of a cowbird chick that was double their size. Cardinal nests are also prone to parasitization and, like the sun rising in the east, I will soon hear the very loud screeching of the cowbird chick in my bushes following an adult cardinal that is desperately looking for something to feed it.

You would think the wren, for instance, would recognize the intruder in its midst. Some types of bird do. The yellow warbler will build an entirely new nest over an existing nest if it spies the larger cowbird egg, neglecting its own eggs in the process of starting over.

But most birds, like the carolina wren and the cardinal, are not programmed that way. If there is an egg, the adult sits on it. And if that slightly larger egg hatches first, as cowbird eggs do, and the chick manages to push some or all of the other eggs or hatchlings out of the nest in order to hog the food, it isn't noticed by the parents. In their minds, they are raising the next generation.

But it's the wrong generation.

In Michigan, where the population of Bachman's warbler was practically wiped out thanks to a nasty combination of habitat destruction and parasitization, it is policy to catch and kill cowbirds within the designated Bachman warbler jack-pine habitat.

It may seem cruel but that has helped the Bachman's population slowly re-grow.

This isn't a problem for the cowbird. This is one bird where the destruction of its usual habitat has helped it.

Cowbirds were farm birds, picking bugs off the cows and the fields. But with "progress" has come suburban developments built on farm fields. There may be fewer farms but the cowbirds adapted and thrived. Too well, in fact.

One thing that amazes me is that after being raised by a pair of cardinals, for example, the cowbird chick will grow up and somehow intuitively know it is not a cardinal. Then it will find other cowbirds and at the correct, programmed time mate and start the parasitation process all over again.

To me this makes the cowbird, literally and figuratively, the dark side of nature.

No comments:

Post a Comment