From The New York Times:
Richard Prum, a Yale ornithologist, was hiking through an Ecuadorean forest 18 years ago when he had one of the strangest experiences an ornithologist can have. He watched a bird sing with its wings. Dr. Prum was observing a male club-winged manakin. The tiny red-headed bird was hopping acrobatically from branch to branch in order to attract female manakins. And from time to time, the male would wave its wings over its back. Each time the manakin produced a loud, clear tone that sounded as if it came from a violin. “I was just utterly stunned,” Dr. Prum said. “There’s literally no bird in the world that does anything that prepares you for it. It’s totally unique.” Ever since, Dr. Prum has wondered how the club-winged manakin managed this feat. Now he and a former student, Kimberly Bostwick of Cornell University, believe they have solved the mystery. Club-winged manakins rake their feathers back and forth over one another, using an acoustic trick that allows crickets to sing.