Durham, NC -- Deep in the scrublands of Keoladeo National Park in northwest India, one thing was hard for biologist Jessica Yorzinski to ignore: It wasn't the heat. It wasn't the jackals. It was the squawks of peacocks in the throes of passion.
From behind the trees in the distance, she could hear a loud two-part whoop, the distinctive call that male peacocks make right before mating.
During the peacock courtship dance, a male announces that he's ready to make his move by dashing towards the object of his affection and emitting a singular squawk before mounting his mate.
"Peacocks have a number of different courtship calls, but this is the only one specifically associated with the moment before copulation, a time when the female is finally right in front of the male. It's called the hoot-dash display," said Duke University researcher Jessica Yorzinski.
The amorous peacock's signature hoot poses a puzzle for scientists.
For one, he's already got the girl.
"By that point she's already right there, checking him out. You'd think that he might not need another signal at such a late stage in the courtship process," Yorzinski said.
What's more, the calls could alert potential predators that an easy meal is near. Wild peacocks make quick snacks for jackals, tigers and hawks in their native habitat in South Asia.
"In a sense, they're advertizing that they're distracted and vulnerable. It would be wise for a predator to capitalize on that," Yorzinski said.
Intrigued, Yorzinski recorded the loud carrying-on of males in mid-conquest. Then she played the calls to free-ranging females in India and videotaped their reactions.
At each site, a loudspeaker played copulation calls on one day and silent controls on another day.
The result: the recorded love sounds made by amorous peacocks in the throes of passion drew eavesdropping females from afar. Females approached and spent more time near speakers that were playing hoots compared to silent controls.
To make sure the birds weren't simply drawn to any noise, Yorzinski repeated a similar experiment with captive birds in an outdoor enclosure at Duke University. There, a speaker played two different sounds: peacock copulation calls, or crow caws.
The results matched what she found in the wild. Captive females paid little attention to the speakers when crow caws were playing, but when the love whoops were played, the females moved toward the source of sound and spent more time near the speaker.
"Why they're attracted to these calls and what it tells them -- these are still open questions," Yorzinski said.
Announcing the fact that he's getting a girl could help a male attract additional mates, she explained.
Studies in other species have shown that females flock towards popular males. "It's like someone's already vouched for him. If he's good enough for one girl, then he might be good enough for another girl, too."
That dating boost could make up for the risks involved in disclosing his whereabouts to potential predators, especially in the birds' native habitat in South Asia where dense trees and grasses make strutting males hard for females to spot.
If distant females are drawn to the love calls made by mating males, what's less clear is what keeps males from boosting their call rate to give the impression that they're more successful than they actually are.
"One of the biggest unanswered questions is why males don't fake it," Yorzinski said. "I've heard males making false calls when there's no mate in sight, so there definitely is some level of cheating going on. Figuring out why they don't do it more often would be the key."
The study will appear in the January print issue of the journal Behaviour, and is available online at http://booksandjournals.
CITATION: Yorzinski, J. and K. Anoop (2013). "Peacock copulation calls attract distant females." Behaviour DOI:10.1163/1568539X-00003037.
The National Evolutionary Synthesis Center (NESCent) is a nonprofit science center dedicated to cross-disciplinary research in evolution. Funded by the National Science Foundation, NESCent is jointly operated by Duke University, The University of North Carolina at Chapel Hill, and North Carolina State University. For more information about research and training opportunities at NESCent, visit www.nescent.org.