Always going after the attractive guy can have its downsides. Female birds gravitate toward flashy fellows, for example, but if they always picked mates with the same showy traits, the population would eventually become inbred. A new study of wild finches suggests a solution to the puzzle: All the males with showy feathers get paired in the spring. In the summer, still-single females fly far from home, where they settle for males with more subdued plumage and thereby contribute to the genetic diversity of the population.
Male finches know how to make an impression. They sport head and chest feathers that can range in color from brilliant yellow to red or purple. Not all males are so stylish, however: Some are as dull brown as the average female. In order to maintain a healthy genetic diversity in the finch population, it would make sense for females to occasionally seek out a color-challenged mate, but biologists were unsure what would motivate them to do this.
Evolutionary biologists Kevin Oh and Alexander Badyaev of the University of Arizona in Tucson tackled the problem by studying an isolated population of finches in Montana that Badyaev has followed for over 10 years. The researchers captured and marked more than 12,000 finches and then studied their mating habits over the spring and summer seasons.
Once female finches hatch, they instinctively leave their parents' neighborhood. But the team found that by the time the females got to their new digs, all the flashy males were already taken. That's because the older females in that location had had their pick of the male litter earlier in the season. Thus, the newcomers were forced to settle for the drab males that were left. This influx of females from another location keeps the population genetically healthy, even though all the girls still prefer the same bright coloration in a guy, says Badyaev, whose team reports its results online April 18 in Proceedings of the Royal Society B.
"It's a nice way of resolving the paradox," says ornithologist Peter Dunn of the University of Wisconsin in Milwaukee. "It's something that a lot of people have been scratching their heads about for five or ten years."