They're Baaaaack!

Uggh! One sure and early sign of spring around these parts is the return of the parasitic nest pirate: the brown headed cowbird.

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.

Here, but NOT Welcome!

Oh, the hated brown-headed cowbirds are back. They return in the spring just before the songbirds that they parasitize so thoroughly. Here's a male (right) and female hoping to fatten up on cracked corn in our side yard.

I won't recount the entire natural history of the brown-headed cowbird, except to say that they evolved following roving herds of bison, eating the insects these large mammals kicked up. Being constantly mobile, cowbirds could not afford to build a nest, incubate eggs, and raise young. So they adapted to let someone else do all the work. Female cowbirds lay their eggs in the nests of other birds. They are amazingly good at finding hidden bird nests and waiting until the coast is clear to slip in and make an unwanted egg deposit.

Two weeks later the "foster" parents are raising a youngster that is not their own (and probably arguing over whose side of the family the nestling's ugliness comes from).

If it weren't illegal and bad for the soul, I'd consider doing something to control this species. Cowbird control measures have resulted in increased reproduction by the endangered Kirtland's warbler in Michigan.


Every year here on our farm we see fledgling cowbirds and it makes me heartsick to think of the wood thrushes, blue-winged warblers, and indigo buntings that were fooled into raising them.

One species that never has to raise cowbirds to fledging is the American goldfinch. Their nests get cowbird eggs to be sure, but the nestling cowbirds cannot survive on the goldfinches' all-seed diet.

Instead of "offing" cowbirds, we'll quit feeding so much corn and mixed seed (which the cowbirds love) and we'll curse these parasites whenever we see them.