Cowbird

It is autumn and cold. Leaves are turning color but unevenly before falling. Then, as I look out my back window, everything turns blacks. My yard is being invaded by a plague of common grackles, about 100 or so. They are all over the feeders but most are on my lawn, turning over leaves for the insects that might be on them or the ground.

During spring and summer the birds found in New Jersey pair off, mate, brood young, teach them to fend for themselves. Then the parents take off for the winter. But there are other birds that don’t travel far and stay together in large flocks. In autumn, these large flocks will hit a field or a lawn, eat what they can and then take off in a noisy cloud of black. On a highway you might see a flock of these dark birds whirling around, blanketing the sky in synchronized flight. In the evening they land in a large field or park lawn.

I find cowbirds to be among the most interesting of these dark autumn birds. The males have dark brown heads and black bodies. The females are a duller, lighter brown. They are found in small groups on fields, parks, even the parking lots of convenience stores, fighting the house sparrows for dropped food. Cowbirds get their name from the days when you’d find them on the farm, following cattle that would churn up insects in their walking. Now, cowbirds come to your bird feeder.

Female cowbirds drop their eggs into the nests of other birds, a process known as parasitization. Despite the egg being generally larger than the host bird’s own, the egg is brooded. It generally hatches before the other eggs and then the cowbird is likely to kick the competition out of the nest. The host parent feeds it as its own. These host birds don’t “see” they are feeding a cowbird chick. Their instinct is to feed their young, even if it does not look like them.

eggs

Here’s why I find them interesting: Somehow, once the cowbird can fend for itself, it knows where to find other cowbirds. They form the small groups you’ll find hanging out with the grackles and blackbirds until spring, when they will pair off and mate.

But for right now, as the leaves change and the wind blows, they blend into the mass of larger, blacker birds that will suddenly appear and shatter the peace of your backyard.

 

This is a contributed post from one of TLC-NJ’s members, Margo D. Beller.

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