Each year barn swallows dart and swoop in summer skies to catch insects. But these flashy blue and orange aerialists aren’t on the hunt for only food. As is true with our own species, barn swallows use athletics and appearance to show off to the opposite sex.
With their distinctive forked tails, barn swallows are widespread. On multiple continents they build mud cup nests under bridges and in barns and other human structures. But their choice of mates varies from place to place.
It turns out that a female European barn swallow chooses a mate based on the length of his tail streamers: the longer a male’s tail streamers, the earlier he’s chosen as a mate.
In North America female barn swallows prefer a different trait—feather color. Male North American barn swallows have a wash of rust on their chest feathers.Biologists Rebecca Safran and Kevin McGraw found that female North American barn swallows choose mates based on the darkness of these chest feathers.Males with a deep rust-colored chest breed earlier and father more young.
But why should chest color matter? The researchers found that males with brighter breast colors have more testosterone than their competitors. This might mean that those males are better able to defend quality nesting sites early in the season.And for many birds strong colors can reflect overall fitness.
So if our species’ focus on glamour and appearance seems shallow at times, remember that for graceful barn swallows beauty does go more than skin deep.