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WhatFemalesWant-ManakinAnatomy A solid wing bone?A solid wing bone?When Kim examined the bone's density, she found something unique. "Every ornithologist knows that birds have hollow bones," Bostwick said. "They're hollow because they need to fly." However, the male manakin's wing bone is solid, and the inside is even more dense than the outside. The wings evolved so that he can create the perfect pitch -- precisely the sound the female is looking for in a prospective mate. Super-sized bonesSuper-sized bonesKim found that the manakin's wing bones were super-sized. In the right half of this image, the large bone with raised bumps is the ulna. If you've ever eaten a chicken wing, you know that this bone should be smooth and narrow. Instead, the manakin has an ulna that is four times wider than it should be. Its large bumps and grooves provide support for the wings, allowing them to move at high speed. But there's more. Good vibrationsGood vibrationsWhen she looked closely at the manakin's feathers, Kim noticed that one wing feather (6) has ridges, while another feather (5) has a curved tip. When the male manakin knocks his wings together, these neighboring feathers act as a spoon and washboard, generating vibrations at just the right frequency. But Kim suspected that wing movement at such a high speed must require extra support, so she ordered a CT scan. Wings as a musical instrumentWings as a musical instrumentRather than using his voice, the male manakin uses his wings as a musical instrument. He leans forward and flicks his wings together over 100 times a second -- faster than a hummingbird beats its wings. How manakins make musicHow manakins make musicKim Bostwick of Cornell University observed these birds 'singing' in "What Males Will Do." She filmed male manakins using high-speed video in order to study how they produce musical sounds. She discovered something astounding. Club-winged manakinClub-winged manakinThis is the club-winged manakin, a rainforest bird the size of a sparrow. If a male manakin hopes to breed, he has to make a sound that is totally unique.