Online at Proc. R. Soc. B: high-speed video and experimental results suggest that male Anna’s Hummingbirds use their tail feathers to produce a chirping sound during courtship displays. This sort of thing is known from other bird species (notably two genera of Manakins), but there was some dispute about how Anna’s Hummingbird chirps. The high-speed video is on You Tube, though it basically only shows a male hummingbird flaring its tail at the bottom of a display dive. The experimental evidence apparently consists of air jet and wind tunnel tests on feathers collected (ouch) from wild birds.
Clark, C.J., and T.J. Feo. 2008. The Anna’s hummingbird chirps with its tail: a new mechanism of sonation in birds. Proceedings of the Royal Society Series B.