The saga of barn-swallow research is a bit like a soap opera; you think you’ve seen the episode before, but if you look closely, there’s an intriguing twist to the tale.
Scientists using the birds as a window on evolutionary biology have found to their surprise that by artificially enhancing the color of male barn swallows’ breast feathers, the males attracted more (and more faithful) females than their duller-chested counterparts: The artificial color also triggered increased levels of the male hormone testosterone sharply and quickly in the “enhanced” birds, at a time in the breeding process when levels ordinarily would be falling.
Researchers had long known that internal chemistry determined the intensity of plumage color. And the team’s previous work had shown the effects of plumage on the males’ breeding success and the relative fidelity of female barn swallows to their beau. This was the first time anyone had shown, in effect, that putting on the Ritz could affect a male bird’s internal chemistry. As the team’s lead researcher, University of Colorado ecologist Rebecca Safran, explains, “the experiment didn’t just improve the male’s looks in the eyes of females, it actually changed their body chemistry.”
The new results suggest that testosterone levels may be closely tied to a male barn swallow’s color and fitness, adds Kevin McGraw, an Arizona State University researcher and member of the research team. The results appear in this week’s issue of the journal Current Biology.