Cowbirds: Engaging in 'Mob' Behavior?

Cowbirds famously deposit their eggs in the nests of other birds, allowing surrogate parents to raise their young. But why do the other birds put up with it? New research suggests the cowbirds are also intimidating enforcers.

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Watch out for those cowbirds. They may make you an offer you can't refuse. Scientists writing in this week's online edition of Proceedings of the National Academy of Sciences report what they call Mafia behavior among the species. Cowbirds are notorious for leaving their eggs in the nest of other birds to be raised. And researchers have often wondered why the put upon hosts put up with new mouths to feed. It turns out if the birds don't accept the cowbird's eggs, the cowbirds just might trash their nest.

For four years Jeffrey Hoover and Scott Robinson of the Florida Museum of Natural History watched cowbirds as they dumped their eggs into warblers' nests in southern Illinois. When the researchers removed the cowbird eggs from the warblers' nests they found that more than half the time the cowbirds came back and tossed those nests like a Caesar salad. Say ya, warbler. You got a mighty nice nest here. Geez, I'd hate to see some guy mess it up. Know what I mean?

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