Female song sparrow
chicks often die if their nest if parasitized by a cowbird - Courtesy,
Dr. L. Zanette
If cowbirds were humans they’d likely be outlaws and driven out of
town. Not only do they lay their eggs in other birds’ nests, they also
destroy some of the eggs that are already there to make sure their own
chicks will get more attention. But it’s not just the adults who are
the bandits of the treetops. Infant cowbirds are advanced juvenile
delinquents. According to Dr. Liana Zanette,
these chicks are such good beggars for food that their smaller, adopted
sisters can’t keep up. As cowbirds have spread across the country, song
bird populations have declined dramatically as a result of this
pressure on the female chicks. Dr. Zanette is an assistant professor of
biology at the University of Western Ontario.
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