How Soaring Birds Tackle Turbulence: Collapsible Wings

How does a bird deal with turbulence? The answer may be in their collapsible wings. By placing a "black box" flight recording on an eagle's back, scientists have found how birds manage to deal with turbulent winds.

In this case, the researchers wanted to see how soaring birds such as eagles, vultures and kites manage to fly in gusty, turbulent conditions that would keep a light aircraft grounded. In order to find that out, they placed a flight recorder backpack on a captive steppe eagle. This flight recorder consisted of a 75 g black box that incorporated GPS and measured acceleration, rotation rate and airspeed.

In all, the researchers analyzed 45 flights. They found that in windy conditions, the eagle collapsed its wings in response to particularly strong gusts rather than hold them out stiffly as an aircraft would. During these moments, the eagle's wings were briefly tucked beneath its body that that it was effectively "falling."

"Soaring flight may appear effortless, but it isn't a free ride," said Graham Taylor, one of the authors of the new study, in a news release. "Soaring may enable a bird to travel long distances but it also puts an enormous strain on its flight muscles. The nature of rising air masses, such as thermals, is that they create lots of turbulence and buffeting that jolts a bird's wings and could knock it out of the sky."

In the past, researchers have suggested several theories to explain why birds perform wing tucks. Now, scientists seem to have our answer.

"Our evidence suggests that wing-tucking (collapsing the wings) is a direct response to a substantial loss of lift that occurs when a bird flies through a pocket of atmospheric turbulence," said Taylor. "We think that, rather like the suspension on a car, birds use this technique to damp the potentially damaging jolting caused by turbulence."

The findings are published in the Journal of the Royal Society Interface.