peacock

Here comes the peacockstepper

By John Upton

What’s hotter than a cutie in decadent clothes?

A cutie in decadent clothes — who can dance like no one is watching.

Sexual selection is a term coined by Charles Darwin to explain why some species have developed elaborately ornamental feathers and antlers — appendages that help woo mates. In humans, it has been argued that sexual selection pressures gave rise to facial hair and ample bosoms.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The elaborate trains of peacocks are among the most classical examples of sexual selection. During breeding time, peahens will visit areas where peacocks vie for their attention with spectacular dances. The peacocks raise their trains in a semicircle and whip them around, sometimes leaning them over the judging peahen. They shake their tail feathers and perform a jig with their feet.

A peahen readied for an eye-tracking experiment. Photo by Jessica Yorzinski.
A peahen readied for an eye-tracking experiment. Photo by Jessica Yorzinski.

A team of researchers set out to try to figure out just what actually interests the peahens during these spectacular courtship displays. They trained captive peahens to wear a patch over one eye and an infrared eye-tracker on the other. Then they watched while peacocks wooed their ridiculously-attired subjects inside black-plastic enclosures that minimized distractions.

After analyzing the footage and data, the scientists realized something surprising. The peahens weren’t looking at the tops of the brightly colored feathers. They were watching the peacocks’ lower regions.

“Based on the scanpath of where the females are looking, you can see that their gaze is focused on the lower train — that is, the lower feathers as well as the legs,” Jessica Yorzinski, an evolutionary biologist who studies animal communication, told Wonk on the Wildlife.

what-peahens-watch

“The peahens may be assessing the width or symmetry of the peacock’s lower train and this could indirectly tell the peahens about the quality of that potential mate,” Yorzinski said. “For example, it’s possible that peacocks with more symmetrical trains produce peachicks that are healthier.”

So what’s the point of having such long and elaborate feathers if peahens are so interested in peacocks’ lower bodies? Yorzinski and fellow researchers explain their theory in a recent paper published in The Journal of Experimental Biology:

Even though we found that the peahens were primarily assessing the lower train, the upper train of the peacock may play an important role in courtship as a long-distance attraction signal in dense vegetation.

In The Descent of Man and Selection in Relation to Sex, published in 1871 (which the researchers awesomely cite in their paper), Darwin noted that peahens can appear coy and uninterested in males, despite the elaborate mating displays. Yorzinski and her colleagues helped explain this phenomenon by discovering that peahens spend more than two-thirds of their time scanning the environment for predators and the like, even as a beautiful peacock dances in front of them.

It’s nice to watch a beautiful dancer, but, from a peahen’s perspective, there’s not much point in finding an idyllically cute male if they’re going to be eaten before they get the chance to mate with them.