How hummingbirds chirp: It's all in the tail

http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2008/02/08/MN6FUU96H.DTL

The title of their UC Berkeley study sums it up: "The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds."

Clark and Feo filmed the birds' plunges and recorded the sound they made at the end of their roughly 50 mph descent from a height of 100 feet or more. High-speed video, at 500 frames per second, showed that the birds started their dives with their tails shut and suddenly spread them at the bottom, for one-twentieth of a second - quicker than a blinking eye.

"Now we have a greater understanding of what's actually going on in really sophisticated behavior by one of our residents," said Robert Dudley, a professor of integrative biology at UC Berkeley. "It's a pretty amazing sort of experiment. It took a lot of initiative, and they put in a huge amount of field time."

Clark and Feo concluded that the squeaks and beeps made by the dive-bombing birds are not vocal - as some research has asserted - but instead are created by their tail feathers.

I love their distinctive little chirp- now I know how they make it.