Study shows fidelity among those females paired with more “desirable” males increases
FEMALE BARN SWALLOWS are known to settle into a nest with one mate, then sneak off to breed with another (or others). In fact, one of every two male barn swallows helps care for at least one chick that is not his offspring. But a new study seems to show that some males are more likely than others to father the chicks they raise. What’s the difference? No surprise here: appearances. A male barn swallow’s breast can range in color from a pale reddish brown to a deep rust. In the study, Cornell University researchers removed eggs from the swallows’ nests to encourage them to mate again. Acting on the assumption that the deeper color was more attractive to females, they divided the males into three groups. Researchers painted the breasts of one group a deep red, painted the second with a clear marker and left the third alone. They then allowed the males to pair up again with their mates.
All of the female swallows stayed socially paired with their original partners. But, as usual, there was some avian hanky panky going on. Both the unpainted male swallows and those marked with clear ink ended up caring for the same number of their own young as the baseline number found before the experiment—on average, 70 percent—or even fewer. But the males painted with the deep red ink fathered, on average, 95 percent of the chicks in their nests. That was the equivalent of one more chick per nest for the more “attractive” fathers.
Similar behavior—that is, increased fidelity among those females paired with more “desirable” males—has been observed in other animals but never tested so carefully, says lead researcher Rebecca Safran.
So can a comparison be drawn between the behavior of barn swallows and other animals—say, humans? Safran says she gets asked that question a lot. “It’s always dangerous to say that something that is true for a barn swallow directly applies to humans,” she says. But, she points outs, many humans spend huge amounts of time and money on their appearances even after they are married. “For better or for worse, appearance is an important indicator of status and wealth—it helps us to define ourselves,” she says—even after we are domestically paired off.