Brown-headed Cowbird

Here are a couple Brown-headed Cowbirds I met last month. As I recently mentioned while discussing Field Sparrows, these birds are obligate brood parasites, birds that lay their eggs in the nests of other bird species and wouldn't even know how to raise their own young.

There's a theory that they developed this strategy so the cowbirds could follow the Bison herds, feeding on the insects the Bison stirred up. They couldn't take care of a stationary nest and also follow those Bison around, or so the theory goes. Of course with relatively few Bison around these days, the cowbirds have taken to hanging around cow herds. (I actually see them on lawns quite a bit too.)

Brown-headed Cowbirds have been known to lay eggs in over 100 different species of birds. Different species react in different ways to the parasitism, ranging from not incubating the egg, expelling the egg, abandoning the nest completely, or unknowingly raising the cowbird as their own.

Some species raise their chicks on mostly vegetarian food; since cowbird chicks need insects to grow properly, they don't do well in the nests of House Finches or Mourning Doves.

Even if you have moral objections to the behavior of brood parasites, there are reasons why you shouldn't remove cowbird eggs yourself.

May 4, 2021 at Duke Farms
Photo 128324265, (c) jpviolette, some rights reserved (CC BY-NC)


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