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American Association for the Advancement of Science

Why good grooming matters for birds

Once barn swallows have chosen their mates for the season, the females may not stay faithful if their males don't keep themselves looking sexy, new research shows.

For male North American barn swallows, the color intensity of their feathers is a signal of "quality." Researchers don't know yet exactly what this quality signal represents -- it might be high social status, good genes, or the ability to raise offspring -- but it plays a critical role when females decide which males to mate with. (Maybe the females judge darker feathers the way some women might appreciate a guy in an expensive sports car or a spiffy suit.)

Rebecca Safran of Princeton University and her colleagues experimented with artificially darkening the feathers of male swallows and then studying how the females reacted. They found that male swallows with darker feathers were less likely to be cheated on by their mates.

The authors say this is the first study to reveal just how sensitive females are to very short-term changes in their mate's appearance; a slightly scruffy plumage at the wrong moment in the breeding season can cause an unwitting male to care for many young that are not his own.

This research appears in the 30 September issue of the journal Science.