Collapsible wings help eagle fight air turbulence

 Soaring eagles tuck in their wings when encountering turbulence to avoid damaging their muscles, scientists suggested on Wednesday, AFP reports.

Zoologists at Britain's Oxford University attached a tiny "black box" flight recorder to a captive steppe eagle (Aquila nipalensis in Latin), a bird of prey with a 1.9-metre (6.1-feet) wingspan.

Housed in a backpack, the 75-gramme (2.6-ounce) gadget monitored the eagle's acceleration, speed and position as it soared over a remote part of Wales while a team filmed the bird from the ground.

Data from 45 flights showed that when the bird was tossed upwards by a hefty gust, it responded by briefly lowering its wings below its body, a move called a wing tuck.

The manoeuvre caused the eagle to dive nose-first, which in turn reduced the aerodynamic load on its wings.

The "wing tuck" lasted for just about a third of a second but was used up to three times a minute in the windiest conditions.

"Soaring flight may appear effortless but it isn't a free ride," said Graham Taylor, a zoology professor.

"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."

Collapsing the wings thus acts like suspension on a car -- a dampener to prevent the bird from being hurt by big gusts.

Eagles are a part of a category of soaring birds that includes vultures and kites. So far, experiments have been carried out with only one bird, so it remains unclear whether other species also resort to wing tucks.

The trick may be of interest to aircraft designers, Taylor said.

While it is unlikely to be adopted by jetliners or other big fixed-wing planes, it may be useful for microlight craft vulnerable to turbulence.