Biggest Bird Flew Without Flapping

July 2, 2007 — The old line, "It's a bird! It's a plane!" could once have applied to the world's largest known bird, Argentavis magnificens, which, with a 23-foot wingspan, was about the same size as a Cessna 152 light aircraft.

A study published in today's Proceedings of the National Academies of Science found that the bird was probably too big to accommodate both wing-flapping in flight and standing takeoff by its own muscle power.

The 159-pound bird, which lived in Argentina six million years ago during the Miocene period, had its own way to taxi down a runway.

"A short run, about 30 feet on a moderate slope, would give enough power — 600 watts — to become airborne," lead author Sankar Chatterjee told Discovery News.

Argentavis then had two lazy means for staying in the air. The first involved soaring over updrafts produced in the Andes foothills, explained Chatterjee, a professor of geosciences and curator of paleontology at the Museum of Texas Tech University.

In the pampas, or plains, where such updrafts are uncommon, the bird could switch to hitching a ride on thermals — columns of air that rise due to natural, sun-fueled heating.

"Once it entered in a thermal, which should have been plenty in the pampas, like modern eagles and vultures, it would circle and climb vertically within the rising column," Chatterjee explained.

"As it reached the top of the thermal, it could glide straight to the next thermal," he added. "This way, Argentaviscould commute 200 miles from thermal to thermal in one day.

Analysis of ancient climate in the region suggests thermals would have been present on most days. During the day, the hefty bird likely spent much of its time gliding and foraging for prey, such as rabbits and hares, which it would have "gulped down whole" with a "formidable beak."

Chatterjee and his team made the flight determinations by plugging wing span, weight and other information gleaned from Argentavis and related birds', skeletal remains into a software program originally designed for studying helicopters.

Lawrence Witmer, professor of anatomy at Ohio University, previously looked at flight patterns in pterosaurs — ancient flying reptiles related to dinosaurs — with Chatterjee and his team.

"Argentavis was crazy big," Witmer told Discovery News. "The challenge for the scientists here was to tease apart information from the remains of a bird that was so far out of the range of modern experience."

He thinks the new theories "make sense and are quite possible," especially concerning how such a bird could have achieved takeoff.

"The biggest problems faced by both birds and human-designed aircrafts are takeoffs and landings," Witmer said. "Some airplane gliders are towed into the air by other planes. It sounds like Argentavis solved the problem through its running takeoff."