When Squirrels Fly

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The basic mechanism behind — or, rather, beneath — the animal’s aeronautic engineering is a loose, fur-covered flap of skin called a patagium that extends along each side of its body from front ankle to rear ankle. Coming out to commence its nocturnal, tree-to-tree travels in search of food, the flying squirrel flings itself from a branch and plummets earthward to gather speed, then spreads all four legs apart, stretching out the flaps of skin. The result is a flat, squarish “wing” surface that extends continuously from its feet on one side and across its belly to the feet on the other side. Picture a tiny, furry flying carpet with a head in front, a tail behind and a foot at each corner.

Now in a glide, the animal steers right or left toward its destination — usually a tree trunk — by raising or lowering its “arms” and leaning, like a child imitating Superman. Its flat tail serves as a stabilizer, much like the tail on a kite. Hardly limited to a straight descent, the flying squirrel can veer right or left, or even spiral 180 degrees, to maneuver around trees, limbs or other obstacles.

As it approaches its destination, the little squirrel may be traveling between 5 and 10 mph (some have been clocked at 30 mph). To brake, it raises its forepaws and the front of its flat “wing,” much like a cancan dancer lifting her skirt, and lands vertically with a click of grasping claws. Immediately, the little squirrel scampers to the other side of the trunk — an instinctive defense mechanism to avoid owls and other predators. From there, the rodent may run to the ground to dig for food, or climb upward and continue its journey to the next tree and the next, sometimes running along limbs, more often jumping and gliding.

Just how far can a flying squirrel fly in a single bound? Most flights are relatively short, between 30 and 80 feet, but glides of 150 to 200 feet aren’t uncommon. Logistically, it all depends on the height from which a squirrel jumps. Upon encountering flying squirrels in the New World in 1743, the English naturalist/explorer Mark Catesby got it about right when he wrote in his journal:

“When I first saw them, I took them for dead Leaves … They will fly fourscore Yards from one Tree to another. They cannot rise in their Flight, nor keep in a horizontal Line, but descend gradually, so that in Proportion to the Distance the Tree they design to fly to is from them, so much the higher they mount on the Tree they fly from.”

Just why flying squirrels glide rather than perambulate on terra firma is likely a matter of energy economics — and survival. The squirrels don’t store energy as fat, so they must forage for food more or less continually during their waking hours. Gliding is a faster and more energy-efficient way to move between widely scattered food sources. For its size, a flying squirrel can cover a lot of ground in a few hours of foraging — far more than it could on foot. What’s more, traveling by air at night is simply safer for a little squirrel — especially for one with baggy pants. Because of its floppy patagium, a flying squirrel isn’t able to run much better on the ground than you can in a sack race. In the air, however, it is a swift and elusive target.

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