"Makeover" Birds Get Testosterone Jolt

Brian Handwerk
for National Geographic News
June 9, 2008

The old adage "image is everything" appears to be true—at least for barn swallows.

Male birds who got richly colored "makeovers" attracted more females and made competing males jealous in a recent study.

The responses from their peers created a spike in the newly colored males' testosterone.

(Related: "Testosterone Gives Male Birds Their Color, Scientists Say" [November 22, 2006].)

The research, led by University of Colorado, Boulder, ecologist Rebecca Safran, demonstrates a dynamic link between external appearance and biological change.

"How did behavior and appearance become linked, so that a male with newfound status begins behaving like a top male? He's not looking in the mirror and saying, Hey, I'm the darkest male around," Safran said.

The males' improved appearance and status were instead mirrored, in a sense, by the response from other birds.

Dominant Behavior

Safran and colleagues made 63 birds appear more desirable by darkening the red breast feathers that females find most attractive.

The researchers then released the animals into their New Jersey habitats for recapture a week later.

During the interim the color change, made with a non-toxic marker, caused shifts in the birds' body chemistry.

John Wingfield, a professor of neurobiology, physiology, and behavior at the University of California, Davis, was not involved in the study.

Continued on Next Page >>


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