July/August 2009

Flying squirrels are so important to the forest that a forestry professor at UAF once called them “the spotted owls of the boreal forest,” after another old-growth loving species that has shut down a few logging operations in the Pacific Northwest. 

To appreciate the northern flying squirrel, tie a bed sheet to your wrists and ankles. Then climb to the top of your house. Leap.

Leading with your nose, glide toward a telephone pole. On the way to the pole, swerve around power wires and tree branches. Just before you smack into the pole, lean back and flare your legs so that your feet and hands land at the same time. And do it all on the blackest night of January.

“It’s pure aeronautical engineering,” said Sanjay Pyare, who has watched flying squirrels glide through tall trees in the Sierra Nevada of California and on Prince of Wales Island in Southeast. He has trapped and later released them, allowing him to enjoy one of the more spectacular shows put on by a small mammal.

“When you turn them loose, they scamper 150 feet up a spruce tree, get their bearings, then drop 70 to 80 feet in a free fall,” he said. “Then, they bank left, bank right, and nail the tree they’re looking for. Then, you throw in the fact that they’re doing it in complete darkness.”

Pyare is professor at the University of Alaska Southeast who has tracked the northern flying squirrel through the towering Sitka spruce, hemlocks and red cedar of Tongass National Monument. He studies them because people know the squirrels are important to the forest—so much so that a forestry professor at UAF once called flying squirrels “the spotted owls of the boreal forest,” after another old-growth loving species that has shut down a few logging operations in the Pacific Northwest.

Supple, cuddly looking Glaucomys sabrinus might be as plentiful in Alaska as the chattering red squirrel, though no one seems quite sure about that. The most frequent encounters with them come at bird feeders after dark. Marten trappers sometimes find they have caught flying squirrels instead of the species they were hoping for.

Most of the flying squirrel’s work in the forest is done under cover of darkness. Though the squirrels will eat meat scraps and a wide variety of other things, they seem to prefer the truffle, the fruiting body of a fungus. Truffles are tubers, some the size and texture of potatoes. By examining the scat of flying squirrels, Pyare has found spores of truffles he didn’t know existed in Southeast. Flying squirrels are skillful at finding those subterranean fungi, sometimes digging as deep as a foot to extract them.

Unlike other fungi that have mushrooms as their fruiting bodies, truffles depend on something—like a flying squirrel—to dig them up, eat them and then deposit their spores elsewhere. Those spores have a symbiotic relationship with tree roots, clinging to the roots and gaining nutrients, while their size and shape helps trees take up water and minerals.

“There might be some kind of a co-evolutionary relationship between these small mammals, fungi and trees,” Pyare said.

Biologists have recognized the flying squirrel’s special role in the forest for years, and Pyare studies them in the Tongass because part of the Tongass Land Management Plan was to set aside reserves of old-growth trees to accommodate this exceptional little creature.

“They’re a strong indicator of forest integrity and how a landscape is functioning,” Pyare said. “They don’t do so well in clearcuts—their movement capability there is basically nothing.”

Flying squirrels live anywhere in North America with coniferous forests and they exist in Alaska as far north as there are tall trees. On Prince of Wales Island, flying squirrels use the plentiful cavities in the ancient rainforest trees for denning.

In Interior Alaska, where nights are bitter cold in winter (and often in fall and spring), flying squirrels seem to prefer the witch’s broom, a spruce tree’s reaction to a rust fungus. A witch’s broom resembles a tangle of dead twigs the size of a basketball.

One of the few biologists to study flying squirrels in the Interior was Bob Mowrey. In the early 1980s, he and John Zasada tracked flying squirrels during the summer, finding that a few hunkered during the day in woodpecker holes or other cavities in birch and aspen trees. But when the temperature dropped sharply at the beginning of November, they noticed that nine out of 10 flying squirrels moved to witch’s brooms, and, to the biologists’ surprise, flying squirrels would pile in together on cold nights. People outside Alaska have also noticed the unique grouping behavior of flying squirrels, something other squirrels don’t do.

“There’s been nest boxes with 10 or 12 adults, with both sexes,” said Pyare.

One reason the squirrels probably group up is to stay warm. Pyare said they remind him somewhat of bats when he’s holding them.

“They’re almost all skin, totally exposed, with very little body mass,” Pyare said, “Heat loss, I’m guessing, is a huge issue in the winter.”

Though they may reduce their activity when they’re huddled up in extremely cold weather, flying squirrels don’t hibernate. During the constant light of summer, they keep a similar activity schedule, even though it remains light enough to read a book outside for 24 hours. The best flying-squirrel show I have ever seen occurred when I came home from the Midnight Sun Baseball Game in Fairbanks one summer solstice. In the dusky light of 2 a.m., I watched three squirrels glide over the house and around the forest, landing on spruce trunks and scampering up the trees again to gain elevation for their next launch. Some of the glides were 50 feet, and I cringed until they flared. The soft landing was pure magic.

How did these unlikely creatures of the night evolve? Pyare said flying squirrels are closely related to tree squirrels. Red squirrels, especially nervous young ones pursued from below, will vault from tree to tree for impressive distances (I’ve heard you should place a platform bird feeder nine feet away from trees to keep red squirrels out). It’s not too much of a leap to imagine squirrels slowly evolving flaps of skin (called the patagia), and a flat, rudder-like tail to glide around in a manner less vulnerable to ground predators. And perhaps their big, teddy-bear eyes help the flying squirrel see at night, thereby avoiding direct competition with other squirrels that are active only in daytime.

Though these hang gliders of the night aren’t rare in Alaska, relatively few people have seen them perform, because most of us keep the same hours as red squirrels. It took me a decade of living in Alaska before one scratched at the window feeder one night, and I had a new favorite creature—one that glides through the dark while we sleep, the dream-catcher of the boreal forest.

Ned Rozell is author of Alaska Tracks: Footprints in the Big Country from Attu to Ambler. Read his blog at alaskatracks.com