Bird "sings" with its feathers

From National Geographic News:

http://news.nationalgeographic.com/news/2009/11/091111-birds-sing-feathers-wings.html

"She knew from previous work that the frequency of the sound made by the manakin was 1500 hertz—1,500 cycles per second. If the two feather types were making the sound, they should resonate when vibrated at the same frequency during the experiments."