January 24, 2008

New Study Explains Evolution of Bird Flight

A letter published in the advanced online publication Nature has revealed new insight into the evolution of flight in birds.    The issue has remained controversial among scientists, and previous theories have usually been based on interpretations of various fossil forms.  

However, this new report is based on experimental observations of young birds, and suggests wing-stroke dynamics are the key to understanding the evolution of avian flight.

The research was led by Ken Dial, Life Sciences Professor at University of Montana, and conducted by scientists at the University's Flight Laboratory.

"There has been a fair amount of interest in the origin of birds and bird flight for at least a century-and-a-half, but I think sadly it has been approached from an awkward beginning," said Dial, the paper's lead author, in a BBC News interview.   

Scientists investigating this area tend to fall into two camps, he said. Those who believe that birds learned to fly from the "top down", by falling out of trees and gliding, and those who think that birds took to the air from the "ground up", by running and flapping their wings, possibly to escape predators.

Both scenarios suggest that birds would first need to establish a wide range of wing movement in order to become airborne.

Previous research conducted by Professor Dial had shown that birds use their wings when running up steep inclines.   This was an important discovery, and something scientists hadn't truly appreciated before, Dial said.    The new research completes the rest of the story.

Professor Dial and his colleagues used high-speed video to study the wing movements of chukars, small quail-like birds, as they ran up steep inclines, glided back down, and then flew. 

"To my amazement, the data kept coming in showing they were not changing [their wing angle] at all," Professor Dial told BBC News. 

"This is one of those moments when you slap your forehead and say "ËœWe've been thinking that the wing-stroke is highly specific for different movements, but it turns out that Mother Nature just needs a single wing stroke to accommodate all these behaviors'."

The team studied a wide range of different bird species, and each time found the same narrow angle range used by the birds.

Professor Dial's team also examined wing movements of fledgling birds as they learned to fly.  They observed that even though the hatchlings had small, stunted wings and were unable to take to the air, they flapped their wings at the same angle as older birds to help speed them up the inclined ramp.   The scientists further found the birds held their wings at the same angle when gliding back down from the incline as well.  

The researchers believe that the wings of baby birds resemble the partially formed proto-wings found on some dinosaurs.  Dinosaurs may have evolved wings to help propel them over rocks and other obstacles that littered their terrain, Professor Dial said.

As their wings grew bigger and became strong enough to support their body weight, flapping them at just the right angle would have let the dinosaurs take to the air, the team concluded in the report.

"That simple wing stroke seems to be elementary to bird evolution and bird ecology to get through the fledgling stage," he added. 


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University of Montana Flight Laboratory