Tuesday 19 June 2012

Bird's rare solid wing-bone developed for wooing


Cornell researchers first reported in 2005 on the ability of these birds to rub specialized wing feathers together to produce a high hum. Now they report in the June 13 edition of the Royal Society journal Biology Letters that these are the first flying birds known to have solid wing-bones. This is what allows these birds to produce their courtship sounds.
In the male club-winged manakin, the ulna (analogous to a  in the forearm) is ridged, solid instead of hollow and 3.5 times the volume of other similar-sized birds' ulnae, including other manakin species. Special sound-producing feathers attached to the ulna resonate to make the courtship tones. The researchers also found similar but lesser adaptations to the humerus, which is the same as the  between elbow and shoulder in humans.
The researchers believe the large, dense bones are adapted for courtship and come at a cost to efficient flight where lighter, hollow bones are ideal. The adaptations offer an extreme example of a species modifying a body part to attract a mate, but with a presumed cost to its fitness.
"The idea that there's this conflict between  and natural selection is not new," said Kim Bostwick, curator of the Cornell Museum of Vertebrates and lead author of the study. For example, a male peacock's large, showy feathers also inhibit flight but work well to attract females. But with the club-winged manakin, the adaptation "isn't just the feathers and what they look like. This is a functional change at the deepest levels. Ultimately, it's the female that's responsible for this odd bone inside the wing of the male," Bostwick added.
The researchers used microcomputer tomography (CT) scanners to noninvasively obtain complete  of the inside of the bird bones, which could then be reconstructed into 3-D color images.


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