The Cellar - June 9th, 2018: Flying Squirrels

There are 50 species of Flying Squirrels, two in North America, the Northern and Southern.
I told my high school biology teacher they ought to be called gliding squirrels and she agreed.
It turns out we were wrong but not alone, in that the scientific community agreed with us until recently.

http://cellar.org/2017/fly1.jpg

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Until recently, flying squirrels were assumed to be passive gliders, using their expansive patagium—the furry wing membrane that spans from the squirrel’s neck to its forelimbs and back to its hind limbs—to simply prolong jumps across canopy gaps, and to lessen impacts upon landing. During passive gliding, travel occurs along a declining linear path.

Once scientists began studying flying squirrels in the lab, it didn’t take long to discover that there is nothing passive or constant about the species’ flight. Researchers would ultimately document in flying squirrels a wider variety of aerodynamic modifications and flight types than had been described in any other species of animal glider. In a single flight episode, a flying squirrel might use a dozen separate flight-control techniques and—frustratingly for the graduate students and research assistants tasked with documenting the patterns—different squirrels would use different combinations of these techniques. Ironically, the one type of flight that has never been observed in this species is passive gliding.

http://cellar.org/2017/fly2.jpg

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As more and more squirrels flew through wind tunnels and along blocked-off biology department corridors, it became clear that flying squirrels have a marked disregard for basic aerodynamic constraints. For example, the squirrels were frequently recorded moving through the air with extraordinarily high “angles of attack,” which is the angle between the wing—in this case the patagium—and the direction of oncoming airflow. Aircraft typically stall when their angle of attack reaches 15 to 20 degrees. Flying squirrels routinely reach 60 degrees, far exceeding values that would result in the stall and crash of even the most advanced military jets.

In the lab, the squirrels are routinely observed generating lift forces up to six times their body weight, a feat that makes it possible for them to take flight with such things as stolen peanut-butter sandwiches—or, under more natural conditions, enormous pine cones.

Laboratory studies also found that the squirrels fly at remarkably high speeds and have a puzzling ability to control their acceleration throughout the flight. However, the recorded speeds vastly exceed those that could be generated by a glide itself. Somewhere in the flying squirrel’s little body resides a mysterious mechanism that, without the power of flapping or internal combustion, generates exceptional lift, comparable to that of powered flight.

http://cellar.org/2017/fly3.jpg

These photographs were taken during the February full moon which marks the beginning of mating season for the Northerns in Montana.
Strobe lights, high speed cameras, 30 below zero, and every female being chased by a “squabbling squadron of ardent males”.

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