February 5, 2008
Observatory-NY TiMEs
Mystery Solved: This Hummingbird Chirps With Its Tail
By HENRY FOUNTAIN



When a male Anna’s hummingbird<http://photos1.blogger.com/hello/276/4443/1024/IMG_4855.jpg> swoops down over a female in an acrobatic mating display, it emits a loud and quick chirp, closely corresponding in tone to the highest C on a piano. For years, the source of the sound has been the subject of debate. Is it a vocal sound, or something else?



Christopher James Clark and Teresa J. Feo of the University of California at Berkeley have settled the question. The sound, they report in The Proceedings of the Royal Society B: Biological Sciences<http://journals.royalsociety.org/content/p5811h6686217j12/>, is produced by air rushing over the bird’s tail feathers.



Mr. Clark, a doctoral student with the university’s Museum of Vertebrate Zoology, used high-speed video to show that the chirp occurs as the mouse-size bird spreads its tail feathers at the bottom of a dive, when it is traveling about 50 miles an hour.



The researchers experimented by removing the outermost tail feathers of a bird; it no longer produced the sound.



They also tested the outermost feathers in a wind tunnel and discovered that it is the trailing vane of the feather — the edge facing away from the onrushing air — that produces the sound. As the air slips over it the vane rapidly flutters or vibrates like a reed.