[Birdtalk] Cowbirds

[Brenda Kidman]

I knew cowbirds would lay their eggs in other's nests *says bad words under
breathe*, but to see they are smart enough to come back and destroy the nest
if the eggs are removed?  Fascinating, depressing, but fascinating...



A chirp you can't refuse: Cowbirds run 'mafia racket' over eggsBy Randolph
E. Schmid, Associated Press
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*.
*STUDY ABSTRACT *Retaliatory mafia behavior by a parasitic cowbird favors
host acceptance of parasitic eggs
<http://www.pnas.org/cgi/content/abstract/0609710104v1>

"It's the female cowbirds who are running the mafia racket at our study
site," Jeffrey P. Hoover, of the Florida Museum of Natural History and the
Illinois Natural History Survey, said in a statement.

"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 over
four seasons in the Cache River watershed in southern Illinois.

While cowbirds leave their eggs in many other birds nests, the researchers
focused on warblers in the study because warblers usually accept and raise
cowbird eggs.

To see what would happen, Hoover and Robinson watched where the cowbirds
left eggs in warbler nests, and then removed some of them.

They found that 56% of the nests where cowbird eggs were removed were later
ransacked.

They also found evidence of what they called "'farming' behavior," in which
cowbirds destroyed a nest to force the host bird to build another. The
cowbird then synchronized its egg laying with the hosts' "renest" attempt.

"Cowbirds parasitized 85% of the renests, which is strong supporting
evidence for both farming and mafia behavior," Hoover said.

The research was supported by the Illinois Department of Natural Resources
and the U.S. Fish & Wildlife Service.
http://www.usatoday.com/tech/science/discoveries/2007-03-06-cowbird-mafia_N.htm
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