"By looking at these little ungainly creatures" as well as their chicken and turkey relatives, "you might glimpse the strategies involved in the origins of flight," lead researcher Ken Dial, vertebrate biologist at the University of Montana, told United Press International.

The evolution of bird flight has proved controversial for more than a century, with two opposing theories dividing the playing field.

One school, the so-called arboreal theory, argues flight originated with tree-dwelling creatures that developed gliding wings to soften landings. The other, cursorial, theory holds ground-dwellers evolved wings to help improve running and took off from there.

"Both models have run into an impasses despite extraordinary fossil finds," Dial explained. "There's a problem in explaining how the intermediate forms leading up to flight are selected for. How do you get an animal with little dinky wings to fly?"

Dial started looking at birds that might have possessed similar habits to their ancestors, ground-dwellers such as pheasants, quail, chickens, partridges and turkeys. "After they're born, these birds, probably like most of the dinosaurs, hit the ground running," he said. "Their eyes are open, legs are well-developed. They're not like most birds, which are raised in elevated nests parents build, which aren't really a proper model."

These birds frequently beat their stubby wings when walking and running up slopes, and Dial wanted to know why.

Experiments revealed partridges whose flight feathers had been gently plucked out at birth could not scuttle up slopes as steep as untouched birds, while partridges with feathers trimmed with scissors fared somewhere in-between.

Then Dial, along with his adolescent son now entering college, used high-speed cameras to study partridges scaling inclines. They also strapped accelerometers on the birds' backs to measure lift forces.

In findings reported in the Jan. 17 issue of the journal Science, Dial's analysis reveals the partridges "beat their wings as fast as they can, not to lift them as we thought like a wing to the heavens, but to stick them to the ground like a spoiler on a race car," he said.

Also, as the birds start running up steeper inclines, "you can see once they run up vertically, they've attained the wing movement needed for flight," Dial said. Instead of beating their wings horizontally, with flapping directed from head to tail, the wings then shift to going up and down.

Dial suggests ground-dwelling birds evolved flapping to climb slopes. "They're called ground birds, but they prefer to be up high when not feeding on the ground, to go to high vantage points, a bale of hay or a rock or tree, I guess to seek refuge from predators," he said. From there, flapping might have developed into flight.

He said he now intends to analyze the interaction of forces between birds and the ground and to study flapping runs in creatures such as ostriches.

"Dial has provided a realistic behavior actually used by ground-dwelling birds that wasn't really appreciated before," said vertebrate biomechanist Andrew Biewener, director of Harvard University's Concord Field Station in Bedford, Mass. "The fact that this shows you can obtain some benefit even in the intermediate stages of evolving a flapping airfoil is a significant contribution."

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(Reported by Charles Choi, UPI Science News, in New York.)

Copyright © 2001-2003 United Press International

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