Cowbirds, in Berkeley?

Brown-headed Cowbird female (Molothrus ater)
Brown-headed Cowbird female (Molothrus ater)

You probably qualify as a Berkeley old-timer if you can remember the radio ad that goes, “Farms in Berkeley? Moooo!” Some 150 years ago, cows outnumbered people in Berkeley, but since then it’s been curtains for the big ruminants. Today you’ll only find them in Little Farm up in Tilden Park. Hence my surprise at finding a cowbird in Cesar Chavez Park.

Here too, as with the Wilson’s Phalarope, the eagle eyes of Jutta Burger spotted the bird first. It was foraging on the ground above the big picnic area in the south-central portion of the park. It had a body about the size of a blackbird, but light brown and grey with white wing borders, and its breast was a streaky light gray. Its head just didn’t fit that conventional profile. It was rather small, pointed, and it had a stubby beak like a big finch. I had to get my photos home before I could be sure what it was.

The brown-headed cowbird (Molothrus ater) is infamous as a brood parasite. Neither the female nor the male build a nest. Instead, the female drops her egg or eggs in the nest of some other bird and hopes that the other mother will brood and feed its young. More often than not, they do, and at considerable expense. The cowbird hatches sooner than other breeds, is bigger and more aggressive, and may snuff out or eject the other hatchlings from the nest.

Some 220 other species have had their nests invaded by cowbird eggs, and about 140 species are known to have raised young cowbirds. In Cesar Chavez Park, the European Starling is a likely candidate for cowbird predation. So is the Red-winged Blackbird. However, the House Finch will not be so victimized; it feeds its hatchlings a vegetarian diet, which is fine for the finches but not enough for the cowbirds, and they starve.

Links: Wikipedia Cornell Audubon

Leave a Reply

Your email address will not be published. Required fields are marked *