At first, Yorzinski was afraid the weight of the device — about 13 ounces — would inhibit the birds’ normal activities. However, by the end of the familiarization process, which sometimes took months, she said the peahens behaved normally while wearing the eye-tracker — walking, eating and even mating with it on.
“This was a very ingenious way of finding out what this species finds important in the world,” said Eric Knudsen at Stanford University, who studies the nervous systems of birds.
This femeale peacock, a peahen, is equipped with a video camera on her head in order to study how sight plays a role in choosing a mate and other interactions.
In experiments, each peahen was placed alongside two peacocks in an outdoor enclosure. The males vied for attention with elaborate shows, shaking their wings and rattling their train of plumes, hooting and dashing toward peahens if the females appeared ready to mate.
The scientists weren’t surprised when they saw that the peahens looked at each peacock when it fanned its tail feathers upward. But, intriguingly, the females focused nearly completely on the bottom part of the train, close to the ground. They mostly ignored the conspicuous upper fan.
However, the peahens did pay attention to the upper feathers when the lower train was obscured — as it might be if the males were relatively far away and partially hidden by the dense vegetation of the birds’ natural habitat in India. This suggests that the flashy upper train is mostly a long-distance attraction signal, but the lower feathers are more important to close-up courtship.
“It was exciting to literally see through the eyes of the females to learn how they perceive potential mates,” Yorzinski said.
Now Yorzinski and her colleagues are placing eye-trackers on peacocks to see how males judge their rivals. They also plan to alter the appearance of the males’ lower trains to try to figure out what the females find attractive.
Eye-trackers may reveal many other details about how animals behave. “You can imagine investigating what monkeys look at as they swing from branch to branch, or what a cat looks at while it’s stalking a bird — how does it divide its attention between the bird and also the path in front of it?” said neuroethologist Michael Land at the University of Sussex in England. “When red deer males are banging antlers together, what are females looking at to judge them?
“An especially fascinating animal to examine might be the chameleon, because each of their eyes can move independently — chameleons point their eyes in different directions to look for prey, and then bring both eyes to the front to target prey, which they capture by sticking out their tongues,” Land added. “How do they control both eyes and get them to work separately and together?”
Choi is a freelance writer based in New York.