When a bird hits turbulence while flying, it can’t turn on the “fasten seatbelt” sign. Instead, new research shows that it tucks its wings to stabilize its flight.
Scientists were studying the flight of a captive Eurasian steppe eagle (Aquila nipalensis) when they noticed a curious behavior. While soaring, the bird would often briefly fold its wings before resuming its normal flight.A Eurasian steppe eagle. Photograph by Christina Krutz, Radius Images/Corbis
Called wing tucks, these behaviors are not new to scientists: In fact, one of the Wright brothers, Wilbur, coined the term while spending many hours watching bird flight to improve aircraft design in 1908. (See “Wright Brothers Flight Legacy Hits New Turbulence.”)
But the scientists began to wonder if the eagle’s frequent wing tucks somehow influenced its aerodynamics. So the team fitted the eagle with a customized, backpack-like harness equipped with a tiny, super-lightweight data recorder—actually a repurposed autopilot device from a drone aircraft. In this sense, the recorder served as the eagle’s black box, recording speed, altitude, pitch and roll, and a host of other information.
The researchers sent the bird on 45 flights through Brecon Beacons National Park in southern Wales, where they recorded 2,594 wing tucks. The data from their recorder revealed that the bird tucked its wings in response to atmospheric turbulence, according to the new study, published October 14 in Journal of the Royal Society Interface.
In other words, during pockets of bumpy air, the eagle’s wing tucks help keep it from crashing.
“When an aircraft hits turbulence, the whole thing moves. But a bird just tucks its wings and keeps a pretty smooth flight,” said study senior author Graham Taylor, a biologist at Oxford University in the U.K.
It’s Going to Be a Bumpy Ride
Airplanes, Taylor explained, have fairly rigid bodies. When they encounter turbulence, they just bounce around, much to passengers’ chagrin.
An eagle’s wings, however, are much more flexible, and an upward gust of wind can create tremendous stress and pressure on the wings. As a result of this pressure, the eagle’s wings tuck briefly. When the gust abates, the bird continues on. (See “Albatross’s Effortless Flight Decoded—May Influence Future Planes.”)
Managing turbulence is especially important for the Eurasian steppe eagle, which migrates each year from Central Asia to Africa on thermals, or rising columns of warm air, the scientists noted. (See National Geographic’s pictures of birds of prey.)
Though these air columns save energy for the birds, they make for an especially bouncy ride.
The new study is “extremely innovative work with the latest technology,” said Alan Wilson, a researcher at the Royal Veterinary College in London who wasn’t involved with the study.
However, the research was conducted in one bird and should be repeated to show if it’s true in other species, the study authors cautioned.
“One should not blindly assume that the same conclusions will necessarily hold in other species, or indeed in other individuals of the same species,” study author Taylor noted.
On the other hand, wing tucking has been observed in other bird species, and “since the laws of physics are the same everywhere, it is reasonable to suppose” that birds also manage turbulence with their wings.