for National Geographic News
The largest bird that ever flew was an expert glider but was too heavy to fly by flapping its wings, researchers say.
Getting off the ground was a challenge for the 155-pound (70-kilogram) Argentavis magnificens, a condor-like bird that lived in the Andes mountains and the pampas of Argentina about six million years ago.
Despite its massive flight muscles and 21-foot (6.4-meter) wingspan, the giant bird probably could not generate enough lift to take off from a level surface, according to a new study.
Like human hang gliders, Argentavis probably had to run downhill into a headwind to become airborne, said Sankar Chatterjee of Texas Tech University in Lubbock.
"Takeoff capability is the limiting factor for the size of flying birds, and Argentavis almost reached the upper limit," Chatterjee said.
"Heavier birds such as the ostrich had to give up flight."
Once aloft, however, Arentavis was no ostrich. Despite weighing as much as 16 bald eagles, Chatterjee said, "it was an excellent glider, like a sail plane."
The report by Chatterjee's team appears in the current edition of the journal Proceedings of the National Academy of Sciences.
Riding the Winds
The new understanding of Argentavis flight comes from an unusual collaboration between paleontologists and a retired aeronautical engineer.
The researchers took measurements from Argentavis fossils and then conducted their analysis using a computer program designed to study flight performance in helicopters.
"Birds are commonly compared with aircraft, but in reality helicopters are a better analogy," Chatterjee said.
SOURCES AND RELATED WEB SITES