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Flying squirrels can adjust ‘wings’ for complex soaring, speed boost

The Washington Post

For decades, scientists thought that flying squirrels could do little more than glide, controlling their descent from a high point to a low point. But most detailed observations took place in laboratory settings.

The laboratory is not where Alexander Badyaev prefers to be. Badyaev is a University of Arizona professor of evolutionary biology. He was born in Russia, so, when pronouncing the word “squirrel,” he endearingly calls to mind Boris Badenov.

He regularly conducts flying squirrel research in the forests of Montana. A few years ago, he spent night after night staking out a corner of the Bob Marshall Wilderness. It was there that Badyaev saw a female leap up from a tree branch, unfurl her patagia — the winglike material that stretches from front legs to back legs — and soar away in level flight.

It was the start of an aerial demonstration that Badyaev captured with his camera. A pair of squabbling male squirrels glided more than 20 meters with little observable loss in altitude. Others made 180-degree midair turns to escape owls.

Badyaev’s images showed that they were capable of complex aerobatics. But how?

More than 15 years ago, after studying hundreds of specimens, Dick Thorington, the Smithsonian’s resident squirrel expert, had noted an odd bit of cartilage at the end of the wrists of flying squirrels. “What Dick postulated at the time was that these were used for maneuverability in flight,” said Badyaev.

The cartilage is similar to the upturned vertical tips you see at the end of wings on passenger jets.

“By adjusting the angle of the wing tip, the squirrel can generate a substantial lift, modifying the speed, distance and trajectory of its glides midflight,” Badyaev later wrote. What is more, the network of muscles that crisscross the patagium can reshape the squirrel’s “wings,” creating a dynamic surface.

Squirrels can even fly upward and increase their speed. They do this by controlling the air that swirls on either side of their patagia. Vortices of turbulence on top of their patagia are tamed with special hairs on their shoulders that they raise and lower. Squirrels can also direct air under their patagia, giving them lift.

Badyaev made other observations. Since flying squirrels are clumsy and vulnerable on the ground, they are able to leave it quickly. They use their muscular hind legs to leap into the air, gaining altitude before gliding away. “Their jump up is incredibly powerful,” Badyaev said. They routinely leap vertically 2 meters, bursting from the snow and creating a popping sound like opening a bottle of Champagne.