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Peacock pomp makes a rumble: male birds emit sounds too low to be heard by humans.

Unbeknownst to humans, peacocks may be having infrasonic conversations. New recordings reveal that males showing off their feathers make deep rumbling sounds that are too low-pitched for humans to hear.

Other peafowl hear it though, Angela Freeman reported June 13. When she played recordings of the newly discovered sound to peafowl, females looked alert and males were likely to shriek out a (human-audible) call. Peafowl are thus the first birds known to make and perceive noises below human hearing, Freeman said.

If peacocks can rumble, other birds may be able to as well, said Roslyn Dakin of Queen's University in Kingston, Ontario, who studies the visual allure of peacock courtship. "I don't think this is a weird case," she said.

Freeman, an animal behaviorist at the University of Manitoba, was inspired to make detailed recordings of peacocks by her coauthor's impression that their fanned-out feather display curved slightly forward like a shallow satellite dish. She found no evidence that the extended train gives any dishlike help in perceiving sounds, but her recordings did reveal throbs of sound below 20 hertz, the lower limit of human hearing.

Males were most likely to make the sounds during two common gestures. After spreading open the glory of his train feathers, a male shakes them, creating a ripple moving down the sides of the array or sending a shudder radiating outward from the base. During both these classic moves, all a person hears is a leaflike rustling, Freeman said. But infrasound thrums can carry for meters to birds out of sight in shrubbery.

The news that there's more to peacock communication than biologists had imagined doesn't particularly surprise Dakin. Familiar as the bird is, she said, "it's been talked about to a far greater proportion than it's been studied."

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Author:Milius, Susan
Publication:Science News
Article Type:Brief article
Geographic Code:1USA
Date:Jul 28, 2012
Words:306
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