When a male club-winged manakin (Machaeropterus deliciosus) wants to attract a female in the Andean cloud forest, he raises his wings over his back and vibrates a pair of giant feathers to make a "PEEP!" sound (as in video above). A scientist at Cornell University suspected there were odd bones under those strange feathers, so she teamed up with colleagues to do computed-tomography scans of the manakin and some close relatives. Bird bones are hollow, with air pockets that make flight easier. But the club-winged manakin is an oddball. The scans revealed that its humerus, the bone that starts at the shoulder, is solid. The ulna, in the next section of wing, is also solid. It's also just plain wacky: While the other birds' ulnae are long, thin, and smooth with a knob at each end, the club-winged manakin's ulna is shaped like a club and covered with lumps and bumps. (And yet they still manage to fly.) The scientists, who report their findings online today in Biology Letters, think the bumps grasp the ends of the special resonating feathers, which poke through the skin, for better sound control, and that the dense bone may make the sound louder by bouncing it out through the feather.
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