Could P. sandersi fly?

To find out how P. sandersi could take off and stay aloft despite its giant size, Ksepka fed data about the bird's mass, wingspan and wing shape into a computer program designed to predict flight performance. The researchers estimated the bird weighed from 48.2 to 88.4 lbs. (21.9 to 40.1 kilograms).

The model suggested the bird was an incredibly efficient glider, whose long, slender wings helped it stay aloft despite its enormous size. It was probably too big to take off simply by flapping its wings and launching itself into the air from a standstill — instead, like Argentavis, P. sandersi may have gotten off the ground by running downhill into a headwind or taking advantage of air gusts to get aloft, much like a hang glider.

"Pelagornis sandersi could have traveled for extreme distances while crossing ocean waters in search of prey," Ksepka said in a statement. "That's important in the ocean, where food is patchy."

By riding on air currents that rise up from the ocean's surface, P. sandersi was able to soar over the ocean without flapping its wings. Once P. sandersi reached adulthood, it may have been able "to live flying over the ocean for most of the year, coming back to land only to nest, flying for thousands of kilometers over the course of the year," Ksepka said. "It probably landed on islands or remote areas where they could avoid predators when they nested."

Unusually, "it's quite likely it had to molt all its flight feathers at the same time," Ksepka said. Flight feathers need to get molted once they no longer become flightworthy, and the bigger they get, the longer they take to grow back. To deal with this problem, they may have done what birds known as grebes do nowadays, and shed all their flight feathers simultaneously — "at the size they reached, it's very difficult to do anything else," Ksepka said.

Future research can analyze how these birds took off and landed, and how maneuverable they were in the air, Ksepka said. He detailed his findings online today (July 7) in the journal Proceedings of the National Academy of Sciences.