From the New York Times: Mystery Solved: This Hummingbird Chirps With Its Tail.

When a male Anna’s hummingbird 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, is produced by air rushing over the bird’s tail feathers. [continue]