Loud chirps during male hummingbirds' aerial displays come from the birds' tails, not their throats, a new study says.
Anna's hummingbirds make rapid, swooping dives during courtship rituals that are punctuated by high-frequency squeaks.
The sounds—roughly equivalent to four octaves above middle C on a piano—are created when the birds fan their tails as they pull out of fast dives, the study authors say.
Instead of acting like a whistle, which creates sound when air moves through a constriction, the birds' feathers vibrate like the reed in a clarinet.
"This is a new way for a bird to make a sound," said study co-author Christopher Clark of the Museum of Vertebrate Zoology in Berkeley, California.
Clark and colleague Teresa Feo report their findings this week in the journal Proceedings of the Royal Society B.
Richard Prum of Yale University has studied tropical birds called manakins, which strum their wings together to attract mates.
Other experts have proposed this type of resonance before as a way feathers might make sounds, Prum said. But Clark and Feo are the first to demonstrate it.
The pair, Prum said, has "done an elegant job of testing the idea."
Plucked Male
The Anna's hummingbird is fairly common in urban areas of the U.S. West Coast (see map), and the animals frequently perform their diving displays at the University of California, Berkeley, campus.
Clark was studying how hummingbirds control aerial maneuvers with their tails when he noticed that Anna's hummingbirds had unusually shaped tail feathers.
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