Why Male Barn Swallows Mustn't Let Themselves Go
A male North American barn swallow (Hirundo rustica erythrogaster) displaying his ventral coloration. Image © Marie Read
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Once barn swallows have chosen their mates for the season, females may stray 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," perhaps akin to an expensive sportscar or a spiffy suit. Researchers don't know yet exactly what this quality signal represents — perhaps social status, good genes, or the ability to raise offspring — but it plays a critical role when females decide which males will father their offspring.
Rebecca Safran and colleagues now report in the 30 September 2005 issue of the journal Science that male swallows with experimentally enhanced feathers are less likely to be cuckolded by their mates. By taking genetic samples both before and after they modified the male swallows' plumage using non-toxic inks, the authors showed that female barn swallows constantly assess the quality of their mate relative to other males in the population. DNA tests revealed that males with enhanced plumage sired more of the offspring in their nests.
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.
Kathy Wren
30 September 2005
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