Brown-headed Cowbirds

Cowbirds go 'mafia' to pawn off eggs

March 7, 2007
BY RANDOLPH E. SCHMID
WASHINGTON -- Raise my kids, or else!

People have long wondered how cowbirds can get away with leaving their eggs in the nests of other species, who then raise the baby cowbirds. Why don't the hosts just toss the strange eggs out?

Now researchers seem to have an answer -- if the host birds reject the strange eggs, the cowbirds come back and trash the place.

The so-called ''Mafia behavior,'' by brown-headed cowbirds is reported in this week's online edition of Proceedings of the National Academy of Sciences.


Southern Illinois research
''It's the female cowbirds who are running the mafia racket at our study site,'' said Jeffrey P. Hoover, of the Florida Museum of Natural History and the Illinois Natural History Survey.
''Our study shows many of them returned and ransacked the nest when we removed the parasitic egg,'' he explained.

Hoover and Scott K. Robinson of the Florida museum studied cowbirds for four seasons in the Cache River watershed in southern Illinois.

When they removed the eggs cowbirds left in warbler nests, 56 percent of the time the nests were later ransacked.

AP