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Flying through the Forest

Newts from the Field is a seasonal installment written by Wildlands Ecologist Shelby Perry, bringing you the wonders of nature from out in the wilderness.

A number of years ago I took a winter ecology class from emeritus University of Vermont Professor Bernd Heinrich in Maine. My small class of ten or so students followed the renowned naturalist around in the woods by day, and sat around a scarred old table at night recounting our tales of adventure over meals we cooked from scratch on a wood-fired cookstove, also our sole source of heat. That entire week the temperature in the cabin never got above 20 degrees, and indeed when it got that high we all stripped down to our long underwear, so accustomed had we become to the cold. It was during that week, one morning dawning at a frosty -22 degrees Fahrenheit, that I began to really consider what it takes to survive winter as a wild animal in the Northeast.

Each day touring the trails of Bernd’s frozen forest I donned long johns under a bulky sweater, a down vest and wool coat, a scarf, hat, and wool-lined leather mittens, wool pants, and tall neoprene and rubber boots rated to withstand arctic temperatures. The whole class put together was probably toting around a few hundred pounds of winter gear to search the woods for signs of comparatively naked wildlife. One animal, in particular, began to capture my imagination: the elusive flying squirrel.

A flying squirrel forages on a downed log at NEWT’s Woodbury Mountain Wilderness Preserve in Vermont.

Tromping around those winter woods I vigilantly searched for standing dead trees with visible holes in them. I wanted more than anything to see a flying squirrel. Bernd’s book “Winter World” held tantalizing stories of four flying squirrels huddling together for warmth in a hole made by a downy woodpecker, and of one occasion when he discovered ten of them sharing a birdhouse.

“Fly” is a fun, but perhaps inexact word for how flying squirrels travel. They are more accurately described as gliders, and can cover as much as 300 horizontal feet from a high enough perch. This is an efficient method of travel in many ways, but as with everything, there are trade-offs. A grey squirrel can sit at your bird feeder and eat roughly their own body weight in seeds each week, building up an insulating layer of fat. They also have fluffy tails to wrap around themselves for insulation when curled up for a winter nap. Flying squirrels enjoy neither of these conveniences.

They stay thin and agile during winter months, likely a result of their need to “fly” to evade predators. It is fortunate, I might add, that I didn’t have to evade any predators that winter week, as my diet of eating everything I could get my hands on, combined with my heavy layers of winter gear, would have made me easy pickings. Flying squirrel tails are also thinner and flatter than those of their grey and red cousins because they are used as brakes and a rudder when gliding.

A close-up of a flying squirrel looking down from a tree trunk.

Their need to glide may well have exerted even greater pressures on their lifestyle, when you consider that across the globe all of the roughly 50 species of flying squirrels are nocturnal, while none of the 100+ species of day-active squirrels have gliding capabilities. Though it is not fully understood why this might be, one can assume that the very adaptations that make gliding a breeze—extra skin flaps between the fore and hind legs—would subsequently make running an awkward and rather ungainly affair. So, it seems likely that these squirrels shifted their active periods to nighttime to be less visible to those that might chase (and eat) them during the day. Nocturnal hunters, like owls, often use sound cues rather than visual ones. In this environment, a silently gliding squirrel is likely to live longer than one scampering noisily across the forest floor.

The Northeast is home to two species of flying squirrels, the Northern Flying Squirrel (Glaucomys sabrinus) and the Southern Flying Squirrel (Glaucomys volans). However, their nocturnal lifestyles, small size, and tendency to travel higher up in the tree canopy means we humans rarely see them.  Though they can live in a lot of places, Flying Squirrels have specific habitat needs that benefit greatly from wild forests including: nesting cavities, gliding perches of many heights, mature nut-producing trees like oak and beech for food, as well as dark nights away from artificial light.

A flying squirrel sitting on a tree branch.

One good way to spot the elusive flying squirrel is to head out into the darkened forest with a UV flashlight. These are often used to locate caterpillars and lichens, which fluoresce by absorbing the higher energy UV light of the flashlight re-emitting it as lower energy wavelengths. Only very recently did scientists discover that flying squirrels do this too, their bellies glowing a bright bubblegum pink under UV light. This adaptation is still not well understood, but we do know that their large eyes see more wavelengths of light than ours do, allowing them to see into the UV spectrum. Additionally, the bellies of many local owl species have biofluorescent feathers, raising the question of whether mimicry might explain this phenomenon—though it is impossible to say whether the owls are mimicking the squirrels to better hunt them, or the squirrels are mimicking the owls to better evade being hunted. Their florescence may also aid them in locating one another and sticking together.

Much to my chagrin, I never did see a flying squirrel during my Winter Ecology class. In fact, I still haven’t seen one despite almost certainly having walked by dozens of them sleeping snuggled together in tree-cavities during countless walks through sunlit woods. I did, however, finally get to see one on video last October, after setting up a wildlife camera on a large log at NEWT’s Woodbury Mountain Wilderness Preserve in Vermont. Over the coming year we’ll be using these cameras to try to better understand how wild animals interact with downed logs of large and small diameters. Hopefully through this inquiry we’ll learn about some of the more intangible benefits provided by large downed logs to all the denizens of the forest. This will in turn help Northeast Wilderness Trust support a future with more wild forests…and more homes for flying squirrels.

Photography: Larry Master,