Auklets are bizarre, puffin-like seabirds that nest in huge colonies, sound like trumpets, and smell like tangerines. Their heads are topped with striking, forward-facing ponytails that scientists had long seen as sexual ornaments: The bigger the crest, the sexier the auklet. But in 2010, Sampath Seneviratne and Ian Jones showed that the crests also act like a rat’s whiskers. The auklets use them to sense the walls of the rocky crevices in which they nest; when Seneviratne and Jones taped down these feathers, the birds were more likely to bonk their heads.

After Kane read about this discovery, “the next time I looked at peafowl crests, I saw them very differently,” she says. Peafowl don’t live in rocky crevices, so their crests are clearly not collision detectors. But perhaps, Kane reasoned, they could be vibration­ detectors. When male peacocks fan out their tails, they also shake them at high speeds—about 26 times a second. This creates a stunning visual illusion in which their eyespots seem to hover against a shimmering background. It also creates a rattling noise, and a wave of pressure that could conceivably vibrate the crest of a watching female.

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To test this idea, Kane and her colleague Daniel Van Beveren acquired several peafowl crests from online vendors and zoos. “A lot of the specimens I got in very strange ways,” says Kane. “One bird was a zoo peacock that had the bad luck to fly into the polar-bear enclosure.”

On closer inspection, the team found that the crest has the right equipment to act as a sensor. At the base of each plume, there’s a tiny companion feather called a filoplume. These are also found in other birds, and they’re known to be mechanical sensors: Something shakes the big feather, the big feather nudges the filoplume, and the filoplume triggers a nerve cell.

Next, the team mounted the crests on mechanical shakers and showed that the constituent feathers resonate when shaken 26 times a second—the exact frequency at which displaying peacocks shake their tail feathers. Only the crest feathers behave like this; when the team tested feathers from other peafowl body parts, or from other big-crested birds, none of them resonated at that precise frequency.

Kane was astonished. “Something the length of a peacock tail feather should have a much different resonant frequency to these tiny crest feathers,” she says. “It’s as if you had a bass that sounded like a violin. It just can’t be a coincidence.”

As a final test of the sensor hypothesis, the team used speakers to play various noises at the crest feathers. White noise did nothing. Pop songs, such as “Staying Alive” by the Bee Gees, had little effect. But a recording of an actual peacock’s tail-rattle made them vibrate.

“The study is rigorous,” says Gail Patricelli, an evolutionary biologist from the University of California at Davis, but “there is still a great deal we don’t know.” For example, “given that peafowl have ears that can hear across a wide range of frequencies, what’s the advantage of having this extra low-frequency channel for communication? Perhaps males and females use it as a private channel that doesn’t attract the attention of predators.”