A few clever scientists tested what happens when the chest feathers of a few New Jersey barn swallows are darkened—the extension of a test three years ago that found males with these deeper colors mated more often, Science News reported.
So, marker in hand, rust-colored breast feathers transformed 30 lighter birds to among the darkest. The results? Males formerly exhibiting, well, “girlie-man” behavior turned quickly into Don Juans, with upped testosterone levels and some healthy weight loss. So does a more attractive appearance translate into improved body chemistry?
Kevin McGraw, a co-author of the study (published in Current Biology) and evolutionary biology professor at Arizona State University, thinks so. "Other females might be looking at them as being a little more sexy, and the birds might be feeling better about themselves in response to that." But he noted his surprise at the fact hormonal changes in the birds occurred within one week of their “transformations.”
Of the 30 male barn swallows darkened, testosterone rose 36 percent after seven days. This was during a time of year when testosterone levels normally decrease—as demonstrated by the 33 birds that didn't get the coloring treatment; whose levels fell by half. Perhaps most interesting is the fact hormones are usually in control, dictating changes in behavior and appearance. But perhaps this exchange is a two-way street?
"It's the 'clothes make the man'" idea, said lead author Rebecca Safran, an evolutionary biology professor at the University of Colorado in Boulder. "It's like you walk down the street and you're driving a Rolls Royce and people notice. And your physiology accommodates this." Other researchers suggest that because of the darkened color, those lucky birds mate more often, thereby altering testosterone levels. Maybe it's got to do with intimidations: Other males perceive this influx of dark feathers as a sign of a new pecking order, which boosts the swallows' hormone levels.
As for the weight loss, it's obvious: More mating means more exercise, which means more calories burned.
In a similar study with humans in 1998, die-hard male sports fans experienced a 20-percent rise in testosterone when their teams won. As Safran pointed out, barn swallows are "socially monogamous and genetically promiscuous, same as humans. There are some interesting parallels, but we do need to be careful about making them."
[Originally published at playgirl.com/blog]