Raised by Others, Birds Use Code to Find Their Kind

John Roach
for National Geographic News
October 15, 2004

Reproduction success hinges on several factors, not least of which is finding a mate within the same species. While this is an easy enough task for humans, it is seemingly more complicated for brown-headed cowbirds (Molothrus ater).

The animals are one of the more than 90 known parasitic bird species, so called because they lay their eggs in the nests of other bird species and leave the chick-rearing to other parents.

The fact that the bird is raised to independence by unrelated foster parents prompts biologists to ask the question: How does the cowbird learn what it is and successfully find its way back to the flock to mate with its own kind?

Mark Hauber, a behavioral ecologist at the University of California, Berkeley's Museum of Vertebrate Zoology, is in search of an answer. His findings so far suggest that parasitic birds employ secret passwords of sorts to identify their own kind.

"As it turns out, a young, blind, six-day-old cowbird chick can already discriminate sounds that are produced only by adult cowbirds and similar sounds of other adult birds," he said, referring to one of his several published studies on the subject.

Other findings by Hauber and colleague Paul Sherman at Cornell University in Ithaca, New York, include evidence that juvenile cowbirds inspect and memorize aspects of their own appearance to compare with other individuals they encounter.

Also, the researchers found that adult cowbirds visit young cowbirds while the youngsters are still living with other species. The adult cowbirds help teach fledglings cowbird-specific behaviors before they leave their foster homes.

Meredith West, a professor of psychology and biology at Indiana University in Bloomington, studies how cowbirds learn social behaviors after fledglings join the flock. She said Hauber has done some "clever work in the field" but does not think there is a big secret to how cowbirds recognize each other.

"It's sort of by default that they end up with each other, because nobody else wants to be around them," West said. "There's no magic bullet for when a cowbird says, I'm a cowbird."

Password: Chatter Call

According to Hauber, juvenile cowbirds, which fledge during the summer months, leave their foster parents about two weeks after hatching. By the time the young birds are one to two months old, they are flocking together with other cowbirds.

Continued on Next Page >>




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