Gangsters in the nest: When birds go bad By Charles Leroux
Tribune senior correspondent
Published March 5, 2007

Jeffrey P. ("J. Edgar") Hoover and Scott K. ("Edward G.") Robinson are ornithologists. Those nicknames aren't really theirs, but it seemed fitting to invoke the legendary head of the FBI and an actor famed for gangster portrayals.

That's because the two scientists have discovered that some birds go bad in a most "Sopranos" way.

They explain this in a paper titled, "Retaliatory Mafia Behavior by a Parasitic Cowbird Favors Host Acceptance of Parasitic Eggs," (available at the National Academy of Sciences online edition). Their research concluded that cowbirds, members of the cuckoo family (whose isn't?), can become enforcers in their neighborhoods.

"We did the work in the Cache River watershed in southern Illinois," Hoover, who works at the Illinois Natural History Survey housed at the University of Illinois, said in a phone interview. "We put up half-gallon milk and fruit juice containers for the prothonotary warblers to nest in."

"Prothonotary" comes from scribes who wore yellow -- somewhat like these warblers -- robes and hoods. Think of the warblers as innocent neighborhood family folk. The cowbirds are the goons who collect protection payments.

"The brown-headed cowbird," Hoover said, "is a brood parasite. It lays its eggs in warbler nests so the warbler will raise its chicks. The question was why would a bird raise chicks so obviously not their own?"

The answer turns out to be old-fashioned intimidation -- wreck the place, kill the kids. The warblers who reject the cowbird eggs soon learn to ask themselves, "Do I feel lucky?"

The ornithologists found that 56 percent of the nests of warblers who refused the cowbird eggs were destroyed by the cowbirds. The warblers who meekly accepted the eggs that weren't their own suffered retaliation only 6 percent of the time.

The enforcers always were females -- goon-ettes if you will. Sometimes they would wreck a nest and steal the eggs before attempting to place eggs there. The tactic is called "farming" and forces warblers to rebuild, giving the cowbirds nice new nests to invade. Fully 85 percent of rebuilt warbler nests ended up hosting cowbird eggs.

One more thing. If you are with the cowbird anti-defamation league, don't blame the messenger.