The Northern flying squirrel (Glaucomys sabrinus) is one of three species of the genus Glaucomys, the only flying squirrels found in North America. They are found in forests across North America. They are proficient gliders but uncoordinated walkers on the ground. They usually breed once a year in a cavity lined with lichen or other soft material. Except when they have young, they change nests frequently, and in winter a number of individuals may huddle together in a shared nest.
Northern flying squirrels have thick light brown or cinnamon fur on their upper body greyish fur on the flanks and whitish fur underneath. They have large eyes and a flat tail. They can also be identified by their long whiskers, common to nocturnal mammals. Flying squirrels do not actually fly, they glide using a patagium created by a fold of skin. From atop trees, flying squirrels can initiate glides from a running start or from a stationary position by bringing their limbs under the body, retracting their heads, and then propelling themselves off the tree. It is believed that they use triangulation to estimate the distance of the landing as they often lean out and pivot from side to side before jumping. Once in the air, they form an "X" with their limbs, causing their membrane to stretch into a square-like shape and glide down at angles of 30 to 40 degrees. They maneuver with great efficiency in the air, making 90-degree turns around obstacles if needed. Just before reaching a tree, they raise their flattened tails, which abruptly changes their trajectory upwards, and point all of their limbs forward to create a parachute effect with the membrane to reduce the shock of landing. The limbs absorb the remainder of the impact, and the squirrels immediately run to the other side of the trunk or to the top of the tree to avoid any potential predators.
Endemic to North America, Northern flying squirrels are widely distributed throughout much of the continent from Alaska, eastwards to Canada and the eastern provinces, southwards to interior regions of the United States, reaching southern California. They prefer to live in areas with an abundance of conifer trees. They occur in large numbers in deciduous and mixed coniferous/deciduous forests. Other suitable habitats include areas, dominated by spruce, fir, and mixed hemlocks; beech-maple forests; areas with abundant growth of white spruce and birch, alternating with aspen groves.
Northern flying squirrels are social animals. They often form groups of 8 individuals, typically including mature squirrels and juveniles. In addition, multiple individuals have been known to live in the same nest. During the winter months, they gather in same-sex units in order to keep warm. Northern flying squirrels are strictly nocturnal animals. They have two periods of activity during the day: one occurs an hour after sunset, lasting around 2 hours, whereas the other begins 2 hours before sunrise, lasting for 1.5-2 hours. Northern flying squirrels are terrestrial feeders, spending a lot of time looking for food. During the year, each individual may have several dens. Their winter dens are usually cavities in conifer trees. Since they don't hibernate, multiple individuals may live in a single den during this period to conserve heat. These rodents are one of the most aerodynamically sophisticated gliding mammals. They are able to glide for as long as 5-45 meters at a time (20 average), though flights as long as 90 meters have been recorded. Although graceful in flight, they are very clumsy walkers and if they happen to be on the ground in the presence of danger, they will prefer to hide rather than attempt to escape. Primary forms of communication include vocalizations, scent, and touch. The most commonly heard calls are soft, low chirping sounds and a cluck, which is emitted when the animal is feeling danger. These squirrels also emit sharp squeaking calls, chuckling noises, 'churring', 'whining' as well as various musical whistles.
Northern flying squirrels are herbivores (mycophage, granivores). They mainly eat fungi of various species, although they also eat lichens, all mast-crop nuts, tree sap, insects, carrion, bird eggs, nestlings, buds, and flowers. The squirrels are able to locate truffles by olfaction, though they also seem to use cues such as the presence of coarse woody debris, indicating a decaying log, and spatial memory of locations where truffles were found in the past.
Little information is known about the reproductive system of this species. They most likely have different mates during each breeding season, which means they may exhibit either polygynous (one male mates with multiple females) or polygynandrous (promiscuous) (both males and females have multiple mates) mating systems. They breed from March to late May. The gestation period lasts for 37-42 days, yielding 1-6 young with an average of 2-4 per year. Males usually don't participate in rearing the offspring. The babies are born undeveloped with closed eyes and ears, fused toes as well as a cylindrical tail. They are extremely tiny and weigh only 5-6 grams at birth. Their fused toes separate by the 6th day of their lives, while their eyes open after 31 days old. At about 40 days old, young squirrels leave the nest. Complete weaning occurs after 2 months of age, but they often continue living for their mother until 3 months old. They are ready to produce offspring during the summer following their birth.
Being widely distributed and quite common throughout its range, this squirrel is not currently threatened. However, in 1985, the U.S. Fish and Wildlife Service classified the Northern flying squirrel as Endangered due to sharp population decline as a result of habitat loss, caused by forest clearing and recreational activities. In addition, the population in the Appalachians has suffered from the introduction of non-native species.
According to IUCN, the Northern flying squirrel is common and widespread throughout its range but no overall population estimate is available. Today, this species’ numbers are stable and it is classified as Least Concern (LC) on the IUCN Red List.