Dr. Kenneth P. Dial (U of M) and his son Terry (Loyola High) discover that Chukar chicks Offer Insight Into Origin of Flight

The 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.

By JAMES GORMAN NY Times

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.

**************

Biologist Finds Clues to Birds’ Flying Start

By Guy Gugliotta
Washington Post Staff Writer
Friday, January 17, 2003; Page A02

Evolutionary biologists have argued for a century about how birds learned to fly. Did they — or their dinosaur ancestors — run faster and faster until their primitive wings allowed them to take off? Or did they jump and glide between trees until they learned to fly without branches?

The answer, it turns out, may be both.

In research reported today in the journal Science, University of Montana biologist Kenneth P. Dial described how some poor-flying modern birds use their wings to help them gain traction as they run up steep inclines or even straight up vertical walls.

"Like the way spoilers on the back of a race car push the tires to the pavement," he said. The birds flap their wings to hold them against the climbing surface even as their powerful hind legs propel them upward.

The same strategy is what may have enabled small, feathered dinosaurs to get into the trees and develop the flapping talents that enabled them to evolve into flying birds. The technique marries the two sides of the old debate: It is "bottom-up" in that the animal starts on the ground, but "top-down" in that the animal may have needed to be in the tree before it could learn true flight.

"It’s a better compromise between the two extremes," said Luis Chiappe, curator of paleontology at the Los Angeles County Natural History Museum and a bottom-up proponent. "There are people who are always going to stick to extreme ideas, but I’m more inclined to find a middle ground."

Dial said he began the experiments that led to his insight by accident. He was studying barnyard chicks to see how much their tiny wings help them lift their relatively large hindquarters in a vertical jump. When he returned home from a trip, his 13-year-old son, who had been minding the experiments, said the chicks were "cheating." Whatever they were doing to get up the wall, he added, they weren’t jumping.

It was true, but the movements were so fast they were hard to follow with the naked eye, Dial said. So he used high-speed photography — 500 to 1,000 frames per second — to freeze the chicks in the act: "When you’re just watching them, it looks like frenetic fluttering," he said. "But in slow motion it’s beautiful to see — we could see they were running and flapping their wings at the same time."

Dial said he expanded his research to focus on various species of birds known as Galliformes — chickens, turkeys, partridges, guinea fowl, peafowl, quail and pheasant, among others. Known as "ground birds," they could just as easily be described as "table birds." Their large hind legs make them poor fliers, but provide them with attractive dark meat for dinner.

Dial used chukar partridges for his pivotal series of experiments, testing and filming their ability to run up inclined planes. Fully feathered partridges running on a gritty surface did not use their wings until the slope reached 45 degrees, but, then, by flapping and changing their wing angle on steeper slopes, they were able to run up to a 105-degree plane — 15 degrees past vertical.

Clipping and then plucking the partridges’ most important flying feathers caused a sharp dropoff in performance, an indication that the wings play a crucial aerodynamic function in climbing. Even more important, however, Dial found that the birds could not handle slopes greater than 50 degrees when they ran on smooth surfaces.

"If the wings were giving them lift, the [running surface] shouldn’t have mattered," he said. "They wanted to run," and it was clear that the flapping wings were helping the partridges get a better grip on the running surface — not lifting them off it.

This finding had important implications for evolutionary paleontology, where the debate over the origin of flight had been obscured for years by the equally contentious question of whether birds descended from dinosaurs. The evolution and subsequent extinction of the flying — or gliding — reptiles known as pterosaurs occurred independently and has nothing to do with the evolution of birds.

The dinosaur-bird debate still seethes with occasional eruptions, but a consensus has emerged in recent years on the linkage connection, principally because of a rich harvest of feathered dinosaur fossils from China. One example, Caudipteryx, an 18-inch-tall omnivore that lived 125 million years ago, is usually depicted as a bantam rooster-like animal with powerful hind feet and smallish wings.

The problem with the dinosaurs, as with the partridges, said evolutionary biologist Lawrence Witmer of Ohio University-Athens, was that scientists could not figure out how to get the big-hindquartered dinosaur into the trees so it could evolve the big wings and delicate feet of the modern flying bird.

"The tree-down theory has always been appealing, except that scientists have always believed that gliding is an evolutionary dead end," Witmer said. "Flapping is what it’s all about, and this study offers a whole new way to look at it. You’re not getting lift-off with flapping, but you’re getting to heights. These little dinosaurs would have sought trees, either as refuge or as places to hunt. This could be how they did it."

© 2003 The Washington Post Company

http://www.washingtonpost.com/wp-dyn/articles/A4057-2003Jan16.html