How Squirrels Fly

Fascinated by the graceful gliding of these mammals with "wings," scientists take a close look.

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 Stafford is creating several variations of models that will mimic the different characteristics of flying squirrels. "There are many differences. For example, we will test one model with the winglets bent upward, and another with the winglets held flat. By comparing the results of these tests we will be able to determine the function of the winglets. We will know what they do. We are building 26 different models, designed to test our hypotheses about the function of different wing structures."

As I listen to all of this, a larger question occurs to me: Why glide at all? "Gliding may save energy getting from tree to tree," Stafford said. "Predator avoidance may also be a factor. Gliding may simply be the fastest way for these animals to get from one place to another, or get to widely scattered food sources."

Looking for answers, Stafford has been videotaping local gray squirrels—the non-gliders—in the wild to compare their behavior with that of gliders.

Being nocturnal, flying squirrels must have good eyesight, he said. "Even so, they often triangulate distance. You can see how their heads bob just before they take off."

The flying squirrel’s eyes are off to the sides of the head so the animal can spot attackers coming from any direction. But this fact, plus the small size of the head, does not make for great depth perception. That’s why the intended flight path has to be checked out from several angles to establish a workable parallax.

Sometimes a squirrel will drop like a stone for a few frightening yards after takeoff to gain speed. It turns by lowering one arm, just like a kid playing pilot. I thought it must be exciting to watch a creature seemingly in the middle of an evolutionary change, and I wanted to know where all this was leading: Would squirrels someday fill the sky like birds?

Stafford had to smile. "Evolution is not necessarily directional. There are all kinds of gliding animals—mammals, lizards, fish—but their development isn’t necessarily going anywhere. Gliding may be an end in itself."

By Michael Kernan


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