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When a peacock fans out the iridescent splendor of his train, more than half the time the peahen he’s displaying for isn’t even looking at him. That’s the finding of the first eye-tracking study of birds.
In more than 200 short clips recorded by eye-tracking cameras, four peahens spent less than one-third of the time actually looking directly at a displaying peacock, says evolutionary biologist Jessica Yorzinski of Purdue University in West Lafayette, Ind.
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When peahens did bother to watch the shimmering male, they mostly looked at the lower zone of his train feathers. The feathers’ upper zone of ornaments may intrigue human observers, but big eyespots there garnered less than 5 percent of the female’s time, Yorzinski and her colleagues report July 24 in the Journal of Experimental Biology.
These data come from a system that coauthor Jason Babcock of Positive Science, an eye-tracking company in New York City, engineered to fit peahens. Small plastic helmets hold two cameras that send information to a backpack of equipment, which wirelessly transmits information to a computer. One infrared head camera focuses on an eye, tracking pupil movements. A second camera points ahead, giving the broad bird’s-eye view.
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The rig weighs about 25 grams and takes some getting used to. If a peahen with no experience of helmets gets the full rig, Yorzinski says, “she just droops her head to the ground.” Adding bits of technology gradually, however, let Yorzinski accustom peahens to walking around, and even mating, while cameraed up.
“What they’ve done is difficult and marvelous,” says evolutionary biologist Bob Montgomerie of Queen’s University in Kingston, Canada. “But it’s just a first step.”
Now comes a rich world of questions about how to interpret the time peahens spend looking at something. Brief glances don’t necessarily mean a sight is unimportant, cautions Montgomerie, who with Roslyn Dakin at Queen’s has done research on peacock displays. People can pick out information with barely a glance, such as which of two people is wearing glasses or which end of a store rack has the blue shirts instead of the orange ones. Birds may have similar abilities.
The camera setups measure where the eye aims its most sensitive area. But Montgomerie wonders whether peahen peripheral vision might be important, too.
For now, the setup requires that avian subjects can bear some weight. Yet other research devices, such as satellite tracking collars, started big and eventually miniaturized. “It’s early days,” Montgomerie says.
Recordings from cameras on a peahen’s head show a close-up of her eye movements (inset) plus the view in front of her as a flirting male struggles, not too successfully, to capture her attention.
Credit: J. Yorzinski