Aug. 5, UCB -- American cowbirds are parasites of the bird world. Like European cuckoos, they lay their eggs in the nests of other bird species and let someone else raise them. But a new study by UC Berkeley and Cambridge biologists shows that cowbirds thrive with a less ruthless strategy than cuckoos. Rather than killing rival nestmates, a cowbird chick uses them to make more noise and draw more parental attention and food, then eats the bulk of it.