Friday, March 29, 2013
Friday, March 29, 2013
Posted by Bill of the Birds at 9:19 AM
I looked out at the freshly filled bird feeders this morning and there was a male cowbird, all shiny black body and chocolate-brown head. The male cowbirds return first in spring and the females follow a week or so later. Once everyone is back, they begin their traditional business of courting and making whoopee. The male emits (because it can't really be called "singing") a burbling sound that rises in pitch, ending in a piercing squeak. As he vocalizes, he raises his bill to the sky, trying his best to look at once handsome, regal, fierce, and ready for some lady action. In the next week or so, our farm will become a noisy cowbird singles bar.
When the songbird nesting season starts in about a month, the female brown-headed cowbirds will spend their time watching and waiting. They are very clever at finding the nests of other bird species: warblers, thrushes, tanagers, sparrows, vireos, and many others. Once she spots a nest, a female cowbird will inspect it to see if it has eggs in it. If it does, and if she has a fertilized egg ready to go, she may drop it right there in the nest.
Then she simply flies off to look for another male cowbird, another nest of an unsuspecting songbird into which she can deposit an egg. This nest parasitism evolved from the nomadic lifestyle of the cowbird. Cowbirds traditionally followed the large herds of bison as they roamed across the continent, eating the insects the herds kicked up. As the herds moved, so did the cowbirds, a lifestyle which did not leave any time for nest building or young rearing. So the brown-headed cowbird figured out a way to reproduce successfully by having other birds raise their offspring.
My lifer summer tanager was a handsome adult male, sitting on my parents' platform feeder in our small-town backyard. It was feeding a fledgling brown-headed cowbird.
Each spring I have slight urge to do something to help our songbirds avoid being parasitized by cowbirds. And each spring I realize just how futile this would be. We do cut back on ground feeding, especially on offering cracked corn, when the cowbirds are around. Secretly I'd like to ask for a week-long visit from the Fish & Wildlife Service folks who "control" cowbird populations in the Kirtland's warbler's nesting range. They have large, baited cages where cowbirds check in but they don't check out. A cowbird Hotel California.
Alas they are native birds, so, as much as I despise them, I accept them. And sometimes I even sing about them.
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