tags: teratornis, Argentavis magnificens, birds, ornithology, giant bird



Dr. Kenneth E. Campbell, (one of the discoverers) in front of the 25 ft. wingspan Argentavis magnificens. Display from the Natural History Museum, Los Angeles. The feather size from such a bird is estimated to have been 1.5 meters long (60 inches); and 20 centimeters wide (8 inches). [larger] Image source.

Discovered decades ago and formally described in 1980, Argentavis magnificens is the largest bird known. It lived six million years ago during the Miocene period throughout Argentina. It is nearly the size of a Cessna 152 light aircraft, with a 23-foot (7-meter) wing span and weighing approximately 150-pounds (70-kilograms). However, even though this bird's muscles were well-developed, they still were not sufficient to generate enough lift for the giant bird to leave the ground. So how did this, the largest of all birds, fly?

Paleontologists have scratched their collective heads over this question for decades, although at least a few of them suspected that the bird soared.

"Takeoff capability is the limiting factor for the size of flying birds, and Argentavis almost reached the upper limit," said Sankar Chatterjee, a professor of geosciences and curator of paleontology at the Museum of Texas Tech University, and lead author of the newly published paper.

In a new study, an unusual collaboration between Chatterjee and his colleague, Kenneth Campbell, with a retired aeronautical engineer, Jack Templin, they confirmed that the now-extinct Argentavis magnificens was actually a high-performance glider, soaring on thermals and updrafts just as vultures and birds of prey do now.

To carry out this research, the scientists used flight simulation software to learn more about the ancient bird's flight parameters by providing it with the dimensions of the bird's bones. This analysis revealed that Argentavis magnificens, similar to most large soaring birds, was too large to sustain powered flight, but could soar efficiently, reaching speeds of up to 67kph (41mph) under the right conditions.

Apparently, Argentavis relied on updrafts in the foothills of the Andes, known as thermals, which are columns of heated air that are deflected upward over a ridge or a cliff. Thermals provide lift for small aircraft as well as for soaring birds, such as modern-day condors, eagles and storks. It's likely that Argentavis circled upwards on a thermal and then soared from one thermal to another over long distances in what the researchers refer to as "slope soaring". Even though the bird's huge wingspan gave it a 100-foot turning radius, this was small enough that it could continue circling within a thermal as it rose high above the plains to search for its prey.

"But once it was on a thermal, it could easily rise up a mile or two without any flapping of its wings -- a free ride, just circling. Then at the top, the bird could simply glide to the next thermal and in this way it could certainly travel 200 miles a day," Chatterjee explained.

But how did this huge bird become airborne in the first place?

"The hardest part would be taking off from the ground," observed Chatterjee. "It would have been impossible to take off from a standing start."

The bird probably used some of the same techniques used by modern-day hang-glider pilots such as running on sloping ground to get thrust or energy, or running with a headwind.

Analysis of the region's ancient climate suggests that thermals were present on most days. Thus, the bird probably spent most of its time gliding and foraging for prey, such as rabbit-sized mammals, which it would have swallowed whole with its formidable beak.

"Its jaw mechanics were not suited for tearing flesh from carcasses, as in vultures, nor for tearing prey animals apart for swallowing, as in eagles and owls," said co-author Kenneth Campbell, of the Natural History Museum of Los Angeles County.

Argentavis is a member of the extinct bird family Teratornithidae within the avian order, Accipitriformes, which is a predatory group of birds related to storks and New World vultures.

The great kori bustard, Ardeotis tardi, is the heaviest modern flying bird weighing approximately 40-pounds (18-kilograms) and the wandering albatross, Diomedea exulans, has the longest wingspan at over 10-feet (3-meters).

The study appears in the Proceedings of the National Academy of Sciences.

Sources

National Geographic (quotes)

BBCNews (quotes, graphic)

Yahoo (quotes)