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Mating Game is Never Over for Male Swallows: study

September 29, 2005

WASHINGTON — Men who put on a little pot belly after marriage can give thanks that they are not barn swallows. A study published on Thursday shows females of that species keep shopping around even after mating.

And these females aren’t looking for good providers or even good company. They want only the best-looking birds, a research team at Cornell University in New York found.

“The bad news for male swallows is the mating game is never over,” said Rebecca Safran, who led the study while a postdoctoral researcher at Cornell.

“This is something that most humans can relate to — think of how much time and money we spend on our looks and status long after we have established stable relationships,” added Safran, who is now at Princeton University.

For barn swallows, known scientifically as Hirundo rustica erythrogaster, good looks equals a nice red breast and belly, Safran and colleagues report in Friday’s issue of the journal Science. And the equivalent of a little hair dye serves them well.

If the male’s red breast is not as dark as other males, the female is more likely to secretly mate with another male, they found.

Some unfortunate males even rear an entire nest of some other male’s young, Safran’s team found.

For their experiment, Safran and colleagues allowed 30 pairs of swallows to mate naturally and lay eggs. They then stole the eggs so the birds would mate again, and they tested the eggs to determine paternity.

Before the females chose their mates for their second clutch, Safran captured the males and either painted their throats, breast and belly feathers with a red marker, left them alone, or used a clear marker in case smell or some other factor played a role.

Then she let the pairs breed again and DNA-tested the resulting chicks.

All the females remained socially paired with their original mates, but also copulated with other males.

The males with red marker enhancements fathered many more chicks than in the first round of mating.

Males whose color was unchanged fathered the same number or fewer chicks than they had in their first nests.

Bird experts believe that feathers reflect a bird’s overall health, and those of their young.

Different bird species find different things attractive in one another. Some males have long, showy tails, for instance.

“If females are assessing mates on a day-to-day basis, it explains why males continue to maintain costly ornaments even when they might appear to have served their purpose,” said Irby Lovette, director of the Cornell Lab of Ornithology’s Evolutionary Biology program, who helped with the study.

“Our goal is now to understand how certain males keep a better plumage than others,” said Kevin McGraw, who worked on the study and who is now an assistant professor at Arizona State University in Tempe.

“Factors like ultraviolet radiation from the sun, soiling and even feather-degrading bacteria are known to affect the color of bird feathers once they are grown, and perhaps the best males are those who spend more time preening and protecting their plumage.”




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