Do Peacocks Pay a Price for Beauty?

A peacock trying to escape a predator may seem about as practical as a sprinter in a wedding gown. But a recent study in the Journal of Experimental Biology suggests that a peacock’s 5-foot-long train is not nearly as cumbersome as it appears.

Peacocks spend the vast majority of their time on the ground, but flight is their main defense against predators. Graham Askew, associate professor in muscle function and movement at the University of Leeds, wanted to find out whether their bulky trains—which weigh in at over half a pound on average—hinder their ability to get off the ground.

Using a couple of high-speed cameras to document the flight, Askew was able to create 3D models of peacocks ­—some with trains, some without—taking off.

“From there, it’s relatively straightforward physics to work out the velocity of the bird and it’s acceleration,” says Askew. Once he had calculated the rates, he was able to work out how much energy the peacocks put into taking off.

“If there is an effect on takeoff performance it’s subtle,” Askew says. “But I’ve only looked at one aspect of their life where there may be a cost.”

Simply producing these elaborate tail feathers during mating season is a considerable cost—about 3% of a male peacock’s daily energy budget, according to Askew’s estimates. Then there’s the brilliant plumage, which draws attention from peahens and predators alike.

While natural selection favors traits that aid in survival, reproduction, or some combination of the two, sexual selection favors traits that attract mates. Beyond aiding reproduction, these traits are otherwise useless; they can even be detrimental for survival. It’s like when a guy buys a Ferrari—it’s not practical, but it shows the ladies that he has the resources to obtain and maintain an expensive car.

Even Darwin had his doubts about the sensibility of peacock feathers, leading him to write in 1860, “The sight of a feather in a peacock’s tail…makes me sick!” About a decade later, he published his idea for sexual selection.

Askew’s study shows that the peacock’s train has a negligible cost toward takeoff, but it doesn’t dispel the prevailing notion that beauty comes with a cost.

“It’s a little overhyped to say that this overturns our ideas about sexual selection,” said Bob Montgomerie, research chair in evolutionary biology at Queens University, who was not involved in the study. "There are several possible costs, and this is just one of them.”

All things considered, the peacock's train is still not a very useful appendage for survival. But in light of this research, perhaps it's better to compare it to a sprinter in a cape, rather than a wedding dress.