|Chicks Offer Insight Into Origin of Flight|
behavior of chukar partridge chicks, which can run straight up the side
of a hay bale or a tree while flapping their wings, may offer a new
window on the origin of flight in birds.
Feathered dinosaurs may have done something similar, Dr. Kenneth P. Dial of the University of Montana suggests in today's issue of Science. He suggests that they too flapped their primitive wings to help them climb, which brought them off the ground and closer to discovering the aerial possibilities of their wings. Even incompletely feathered proto-wings, Dr. Dial says, would have been useful in running up inclines.
One of Dr. Dial's findings, which has surprised other scientists who study the evolution of flight, is that the chukar chicks did not use their wings to raise them off the ground. The wing beats served the same purpose as spoilers on race cars. The force generated by flapping pressed the chicks into the surface on which they were running for better traction. As Dr. Dial said of his finding, "It's not intuitive."
In fact, he came upon the behavior accidentally. His teenage son, Terry, was helping him study the development of flight in chukar chicks. While Dr. Dial was traveling, his son was keeping track of the young birds as their feathers grew, and they gradually launched themselves on longer flights, horizontally and vertically.
The vertical flights used hay bales as an obstacle. When Dr. Dial returned from a trip, he said, his son told him the chicks were not staying with the program. "They're cheating," Dr. Dial recalled his son telling him, "They're not flying anymore. They're running up."
Dr. Dial had to see for himself. He then had to videotape the behavior and to do experiments varying the incline and the surface the birds were running up, and clipping the feathers at different lengths.
He found that the chicks were using a flight stroke, but changing the angle to press their feet against the running surface. More feathers meant more effective use of the wings, but partly feathered wings provided a significant benefit.
Dr. Dial concluded that proto-birds with somewhat similar wings might have done the same thing, and that the climbing ability they gained would have given them an evolutionary edge, even if the wings were not yet useful for full flight.
Once the proto-birds were up a bush, or wall or tree, they would be in a position to discover what wings could do in the air. This evolutionary path to flight, he says, is different than previous models in which proto-birds first launched either from the trees or the ground, called the arboreal and cursorial models. "It's both and neither," Dr. Dial said.
The findings have intrigued other scientists. "First and foremost," said Dr. Kevin Padian of the University of California, "it's telling us something we never knew."
Dr. Padian, who studies the evolution of flight, said: "Nobody knew that they ran up trees like this. Nobody knew that wings could generate this kind of force. It's a terrific study for those reasons alone."
Dr. Padian said Dr. Dial's demonstration of this new use of wings added to earlier research that had determined that the dinosaur ancestors of birds had both feathers and the right limb structure to make a flight stroke. Even without flying ability, he said, wings and feathers offered evolutionary benefit, in terms of isolation and catching prey. Those dinosaurs, he said, could have used a forward predatory grab similar to a flight stroke. The new use of wings, he said, offers an additional survival benefit for a proto-wing.
Dr. Alan Gishlick, a paleontologist who also studies the evolution of flight, said, the research "for the first time gives us a modern analog for terrestrial origin of flight."
Dr. Gishlick, who is at the National Center for Science Education in Oakland, Calif., a nonprofit group that defends the teaching of evolution in public schools, said the fossils of dinosaurs he has studied showed they had the bone and muscle structure for this use of wings.
"Dinosaurs like velociraptor could have done this," he said.
He was not suggesting that velociraptors flew, since they seem to have been a highly successful predator on their feet. A more likely candidate to want to leave the ground, Dr. Gishlick said, was microraptor, a feathered dinosaur the size of a pigeon that was chased enough to make it want to run up into the sky.
January 17, 2003MORE? (Dino Soar)
The New York Times