Nestled in hollow tree crevices at the highest elevations of the Great Smoky Mountains National Park is one of the park’s more elusive mammals—the Carolina flying squirrel, Glaucomys sabrinus coloratus. A subspecies of the Northern flying squirrel, the Carolina flying squirrel is listed as federally endangered and is found in the southern tip of the species’ range in the highest mountains of western North Carolina, east Tennessee, and southwest Virginia. 

The Carolina flying squirrel can trace its roots back to the last ice age when sheets of ice covered much of northern North America and forced cold-climate plants and animals south. As warming temperatures melted ice sheets, the cold-climate species migrated north and found refuge in the high elevation of the southern Appalachia mountain range. For thousands of years, isolated populations of flying squirrels became increasingly distinct. That evolution resulted in the Carolina flying squirrel subspecies, which biologists first discovered in the early 1950s.

Carolina flying squirrels are small creatures that live in the cavities of high-elevation mixed hardwoods, such as eastern hemlock, northern hardwood-red spruce and red spruce-Fraser fir. Adults range from approximately 10 inches to 14.5 inches, which is just shy of the height of a bowling pin. They have thick fur in three different colors—a light brown or cinnamon on their upper body, greyish fur on the side, and white fur on their bellies. 

Little is known about the mating systems of flying squirrels, but courtship typically begins in March and continues to late May. They have one litter each year with two to four kits in each litter. Raised solely by the female, newborns weigh approximately five or six grams (about the weight of a quarter), have closed eyes and ears, fused toes and a cylindrical tail. Their eyes open after 31 days, and by day 40 they leave the nest. The new litter may, however, stay with their mother another month, but typically breed in the first summer after their birth. Most northern flying squirrels live less than four years in the wild, but can live up to 15 years in captivity.

Food and flight simulation

Their secretive nature has a lot to do with the fact they are nocturnal creatures and usually leave their homes in the treetops to hunt for about two hours after sunset and again an hour before sunrise. Large eyes and long whiskers help them locate their food sources, which range from fungi and lichens to nuts, insects and carrion. 

One particular food they tend to favor above others is the truffle, which is the fruiting body of a subterranean fungus. Truffles are critical to forest health because they form a mycorrhizal relationship—a symbiotic or mutually beneficial relationship—with trees. Truffles colonize the root system of the tree, typically a spruce, and provide an increase of water and nutrient absorption for the tree, which in turn provides the truffle with carbohydrates. Trees with this relationship to truffles grow larger and faster and are less susceptible to drought and disease. The Carolina flying squirrel is a fungivore that first feasts on the earth-flavored treats and then distributes the truffle spores throughout the forests it inhabits.

Despite its name, the Carolina flying squirrel does not actually fly; it glides. A membrane structure created by a fold of skin called a patagium assists the squirrel in gliding and ‘flight.’ From their homes in the treetops, flying squirrels get a running start and leap from the branches. Sometimes they also propel themselves from a stationary position by bringing their limbs under their bodies and retracting their heads before leaping into the air. 

Once in midair, the squirrel forms an “X” with its limbs, which causes the patagium to stretch into the shape of a square. These graceful, gliding creatures move with great efficiency in the air. Their tails act as rudders and help them make sharp turns to maneuver their bodies and take full advantage of their time in what appears to be actual flight. They usually glide between 20 and 30 feet.

When they are ready to land, the squirrels raise their flattened tails and change their trajectory upward. They point all four limbs forward, which creates a parachute effect with the patagium. Their thick paws provide cushion for landing. When they land, they do not stay in the same place for long. They immediately run up or around the tree to escape the eyes of a potential predator. 

Flying squirrels may be graceful in its simulated flight, but when it comes to walking on solid ground, they are extremely clumsy creatures. If they encounter a predator or any type of danger outside of the treetops, they prefer to hide rather than attempt an escape. 

Northern flying squirrels are important prey for the Eastern Screech Owl. The Great Horned Owl and various hawks are among other large birds that prey on the nocturnal flying squirrel. Four-legged predators include the red fox and, outside the park, the domestic housecat. 

Protecting a delicate species

Predators, however, are not the Carolina flying squirrel’s greatest survival challenge. Due to the fact they are so habitat-specific, the increased loss of forests over the years is what led biologists with the United States Fish and Wildlife Service to list it as endangered in 1985. Habitat loss has fragmented the Carolina flying squirrel population, which now lives on ‘sky-islands’ on nine isolated mountain peaks in the southern Appalachians. 

“The population of Carolina flying squirrels is one of many mammals we are tasked with managing in the park,” said Bill Stiver, supervisory wildlife biologist in the Great Smoky Mountains National Park. “Because it is an endangered species, the measures we take usually have to do with compliance work associated with any activities that would occur within the flying squirrels’ habitat.”

Several years ago, park officials partnered with researchers from North Carolina Wildlife Resources Commission to conduct a survey of the Carolina flying squirrel in order to get an approximate location of habitats. Using nest-box surveys, researchers determined what kind of habitat these elusive creatures seek.

“In the park, we usually find them in yellow birch or large beech trees with hollow crevices and cavities,” Stiver said. “If we are going to try and clear some vistas and need to cut down some trees, we monitor the trees to see if they are important habitat. If we think it is, we will survey it to make sure there are no squirrels living in it. We do not want to impact the squirrels directly or indirectly by harming them or destroying their habitat.”

According to Paul Super, science coordinator for the Appalachian Highlands Science Learning Center at Purchase Knob, Corrin Diggins of Virginia Tech and the United States Geological Survey is currently piloting a study in the park to determine if microphones that detect the squirrel’s ultrasonic calls can help determine if a squirrel is using an area. This work is funded in part by Great Smoky Mountains Association. 

A few years ago, researchers with the USGS published a study in Endangered Species Research that provides resource managers with a predictive map based on USGS modeling efforts, which will help to better define, protect and enhance the endangered squirrels’ habitat. 

“The strength of our modeling is that it allows resource managers and other researchers to account for Carolina northern flying squirrels without having to catch them in traps or artificial nest boxes, activities that are time consuming and logistically difficult to undertake,” said W. Mark Ford, an USGS scientist at the Virginia Cooperative Fish and Wildlife Research Unit at Virginia Tech and lead author on the study. “Our findings can be used by resource managers to prioritize forest areas that are habitat for this subspecies.”

A plan for recovery

Decades before the establishment of the park, logging and fires reduced southern forests in size and quality. Forest recovery efforts have helped several species of trees recover, but new threats face these high-mountain forests inhabited by the endangered squirrel. Human-induced threats include the introduction of exotic insects, forest fragmentation and development on private land. Climate change and air pollution contribute to decline of tree species such as the hemlock and red spruce tree.

The red spruce is of particular interest to wildlife biologists working to protect the Carolina flying squirrel. “Southern Appalachian red spruce-Fraser fir forests are among the most imperiled forest ecosystems in North America and are believed to be highly vulnerable to climate change impacts,” Ford said. “The squirrels need red spruce forests for their habitat, where they persist, largely consuming truffles. Conversely, the red spruce forests need the squirrels to help disperse the spores of these truffles that the trees need for nutrients.”

A partnership between the Southern Highlands Reserve and The Nature Conservancy in 2013 established the Southern Appalachian Spruce Restoration Initiative with a focus on the restoration of the endangered high elevation spruce-fir forests by reintroducing red spruce to the mountain environments. 

“The huge decline of spruce due to logging and fires triggered the future impacts we now see on the Carolina flying squirrel,” said Sue Cameron, an endangered species biologist with the U.S. Fish and Wildlife Service and the lead biologist on the recovery plan for the Carolina flying squirrel. The plan outlines steps to recover the species with the goal of eventually removing it from the endangered species list. Included in the plan are actions that are needed in order to recover the species and specific activities biologists and researchers need to take to get to that point, such as surveying potential habitat to locate the species.

Keeping track of the populations after locating them, however, is another challenge.

“These are very secretive, elusive animals,” Stiver said. “That’s part of the problem we face with management. It’s easy to put a radio collar on a big ol’ bear, but trying to put something on a squirrel is challenging.”

For now, Cameron, Stiver and researchers with the Southern Appalachian Spruce Restoration Initiative will have to make do with the information they already know about the habitat the Carolina flying squirrel prefers. “For this particular species’ survival, it really is all about habitat,” Cameron said. 

Out of sight, not out of mind

Most people will never see the Carolina flying squirrel because of its nocturnal nature and high-elevation habitat. It may not ever be a mammal people stop their cars to observe, but it will always play an important role in the ecosystem. 

“This is a species that sometimes spends time in shelters along the Appalachian Trail,” said Super. “I’ve been kept up at night in a shelter by flying squirrels running back and forth across the roof.”

Stiver thinks people should care about the squirrel just like they care about bears and elk and everything else in the park. 

“It’s part of the high-elevation spruce fir northern hardwood forest ecosystem,” he said. “We are mandated to protect all the resources here in the park, including small mammals like flying squirrels and large mammals like bears. They are just part of what makes the Smokies so unique.”

For Cameron, just having a species like the Carolina flying squirrel that exists in the ecosystem is an important fact for people to know. 

“One of the things that makes this world an interesting place is the huge amount of plant and animal diversity. Sometimes you get a glimpse,” Cameron said. “For me, it’s pretty fascinating to know there’s an animal living in our forest that glides through the sky at night and eats truffles.”

Originally published in Smokies Life Magazine, Volume 12, #2