Feathers make the man in world of birds: study
WASHINGTON (Reuters) - Dying the red breast feathers of barn swallows not only won the birds more mates -- it made their testosterone levels shoot up, U.S. researchers reported on Monday.
The dye itself did not change biology -- but it did change the way other birds reacted to the enhanced males, said Rebecca Safran of the University of Colorado at Boulder, who led the study.
They received more attention from females and got into more fights with other males when their reddish breast feathers were intensified, Safran found. This, in turn, caused levels of the "male" hormone testosterone to rise.
"The experimental manipulation didn't just improve their looks in the eyes of the females, it actually changed their body chemistry," Safran said in a statement.
"A male barn swallow can't look in a mirror and assess his social status," she added. "But if he flies into a group of other swallows, the birds will quickly assess it for him and give him a sense of where he fits in."
Writing in the journal Current Biology, Safran and colleagues said they captured 63 male barn swallows in New Jersey at the start of the breeding season, when levels of sex hormones like testosterone are typically declining.
They used a nontoxic marker to color the breast fathers of half to resemble the darkest, most attractive feathers of males within the population. They also tested the blood of the birds before releasing them.
A week later, the birds were recaptured. The marked birds had higher levels of testosterone and had lost weight, perhaps because they had been fighting and making love, the researchers said. Or perhaps they had worn themselves out trying to live up to inflated expectations, said Safran.
Her team showed in 2005 that male barn swallows given darker breast colors bred earlier in the season and fathered more young. Their mates also cheated less often with other male suitors.
"The results provide strong evidence that color is an important indicator of male quality," Safran said.
Similar signals are seen among deer with big antlers or birds with flashy tail feathers, she noted.
Even human males may be affected -- for instance, a man who wears an expensive new suit. "When he says he feels like a million bucks, there probably is some biochemical feedback going on," said Safran.
"The result is something we all might experience when given the chance to upgrade our status, like winning a prestigious award or being invited to an exclusive event."
(Reporting by Maggie Fox, editing by Will Dunham)