Scientists Solve Mystery of the Wishbone: It’s a Spring
BOSTON (AP) _ The first X-ray movies of birds in flight have revealed the function of the wishbone: It’s a spring.
Scientists who made the discovery suspect that the flexible, V-shaped bone helps birds breathe while they fly. Bird experts had assumed that the bone was simply a strut between the shoulders.
The idea that this bone is springy probably won’t come as a surprise to anyone who has made a wish after Thanksgiving dinner and tried to snap a turkey’s wishbone before it’s had time to dry.
″This is well known to everybody in the world,″ said Farish A. Jenkins Jr. of Harvard University. ″It’s only scientists who discover the obvious.″
Jenkins made his observation by coupling two common research tools: the wind tunnel and the X-ray movie, similar to those used by doctors to study heart disease.
He and two colleagues, Kenneth P. Dial of Harvard and George E. Goslow Jr. of Northern Arizona University, took X-ray films of starlings flying in place against 20-45 mph winds.
The movies allowed a look inside the birds at how the various bones work during flight. Until now, researchers have tried to figure out such functions by looking at the skeletons of dead birds or the outsides of live ones.
″It’s a pioneering new method of studying birds,″ said Robert Raikow of the University of Pittsburgh. ″We can actually see the movement of the skeletal elements during flight. That’s pretty exciting.″
In a report in Friday’s issue of the journal Science, the team described the way the wishbone bends each time a bird flaps its wings.
″The wishbone turns out to be a spring,″ Jenkins said in an interview.
At rest, the upper ends of the starling’s wishbone are 11 or 12 millimeters apart. But when the wings descend, that distance stretches to 18 to 20 millimeters.
Just why it bends this way is not entirely clear. Jenkins said the spring doesn’t seem to help the bird beat its wings more efficiently. Instead, he theorizes that it helps the bird breathe in more air during flight so it can burn the energy it needs to stay aloft.
When a bird breathes, air flows first into air sacs scattered throughout its body and then into its lungs. Among these sacs is one between the two arms of the wishbone.
The researchers speculate that as the bird beats its wings downward, the wishbone spreads apart, opening the air sac so it fills with air. Then, on the upswing, the bird’s sternum squeezes the air out again.
″What we suspect is that there is an alternating bellows mechanism drawing air in and out of the sac and possibly in and out of the lung,″ said Jenkins.
Not all birds have wishbones - hummingbirds and some parrots are among the exceptions - but Jenkins believes the starling’s wishbone spring is typical of most feathered creatures, including the Thanksgiving turkey.