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Starlings star in X-ray movies.

Starlings star in X-ray movies

To trace the intricate motions of bird flight, researchers have made what they say are the first X-ray movies of flying birds. In doing so, they have identified two skeletal movements that may help birds meet the increased metabolic needs of flight. Previous knowledge of bird flight has come from conventional photography, which does not directly reveal the mechanics of muscular-skeletal interaction.

European starlings flew in a small, room-sized wind tunnel at speeds of 20 to 45 miles per hour while being radiographed from the side and above, at 200 frames per second. Analysis revealed that on the downstroke of the wings, the wishbone, which joins the shoulders, bends and widens; on the upstroke, it recoils. The sternum also moves, rising upward on downstroke and descending on upstroke, the researchers found.

Because the wishbone shafts lie close to an air sac -- an apparent reservoir for extra air -- in the starling's upper body, the researchers envisioned a functional relationship between the two structures. When they artificially inflated the sac, the wishbone spread, supporting that hypothesis. Based on their observations of wishbone spread (presumably inflating the shoulder air sac) and simultaneous upward movement of the sternum (apparently compressing posterior air sacs)--all in synchrony with wingbeat--the researchers further suggest that most small and medium-sized birds, including starlings, may have a secondary method of moving air between air sacs and lungs, beyond normal inhalation and exhalation.

The research, conducted by Farish A. Jenkins of Harvard University, Kenneth P. Dial of the University of Montana in Missoula and George E. Goslow of Northern Arizona University in Flagstaff, is described in the Sept. 16 SCIENCE.

The new work grew out of a comparative study of mammalian and reptilian patterns of locomotion and neuromuscular control. "We wanted to describe the basic relationship of form and function and how various structures of the shoulder and wing worked for birds," Dial says. "Previous studies relied on traditional methods of dissection and interpretation. We were interested in making actual measurements of how these structures perform." Future investigations by the group will include study of the relationship of shoulder design to wing type and flight mode.

The process of studying a dynamic, movable skeleton, Dial says, is "a thrill. But it takes a lot of work to get the birds to fly. Only 1 in 5 really cared to fly in the tunnel."
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Title Annotation:first X-ray movies of flying birds
Author:Eron, Carol
Publication:Science News
Date:Sep 17, 1988
Words:398
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