Glaucomys sabrinus
northern flying squirrel

Glaucomys sabrinus ranges from the treeline in Alaska and Canada southward in the west to northern California and Colorado, in the middle of the continent to central Michigan and Wisconsin, and in the east to northern North Carolina and Tennessee. Island populations exist in areas of high elevation in other parts of the United States, including the southern Appalachian Mountains, the Black Hills, and the Sierra Nevada.

Most often found in areas dominated by conifers, northern flying squirrels can also be relatively abundant in deciduous and mixed coniferous/deciduous forests. Glaucomys sabrinus has been found in diverse areas including regions dominated by spruce, fir, and mixed hemlocks, in beech maple forests, and in areas dominated by white spruce and birch with interspersed aspen groves. The northern flying squirrel often nests in conifers 1 to 18 meters above the ground. The nests are made of twigs and bark, and they are softened with feathers, fur, leaves, and conifer needles.

Glaucomys sabrinus weighs between 75 and 140 grams, and ranges from 275 to 342 mm in length. It has silky grey and cinnamon brown fur, with white tipped and grey based belly hairs. Northern flying squirrels have a furred patagium (fleshy membrane) that extends from the wrist of the foreleg to the ankles of the hindleg. The tail is furred, flattened, rounded at the end, and long (80% of the length of the head and body). Glaucomys sabrinus has large black eyes, which it uses for nighttime activity. Southern flying squirrels, which appear similar to the northern flying squirrels, can be distinguished because they are smaller and the hairs on the belly are often white all the way to the base of the hair. The dental formula for Glaucomys sabrinus is 1/1, 0/0, 2/1, 3/3 = 12/10 = 22.

Not much information is available on the mating system of northern flying squirrels. Individuals most likely have different mates each breeding season.

Courtship begins in March and may continue until late May. One litter is born per year, and the female raises the young without the help of the male. Copulation occurs in early spring and is followed by a gestation period of 37 to 42 days. Usually, 2 to 4 young are born, though litters as small as 1 and as large as 6 have been recorded. Newborns are poorly developed; they weigh 5 to 6 grams, and they have closed eyes and ears, fused toes, and a cylindrical tail. By the sixth day the toes are separated, and the eyes open after 31 days. Young leave the nest at 40 days and are totally weaned after two months, though they may remain with the mother another month. Flying squirrels breed in the first summer after their birth.

Young flying squirrels are born helpless and are nursed and cared for by their mothers until they reach independence.

Most northern flying squirrels live less than four years in the wild.

Glaucomys sabrinus is clumsy on the ground, but can glide gracefully from tree to tree. Northern flying squirrels sometimes share nests and may live in groups of up to 8 adults and juveniles. Individual Glaucomys sabrinus aggregate into single-sex groups for warmth during the winter. Strictly nocturnal, northern flying squirrels are active for about two hours beginning an hour after sunset, and again for an hour and a half to two hours before sunrise.

Depending on the habitat, the home range of northern flying squirrels ranges from 0.8 hectares to 31 hectares. Female northern flying squirrels are territorial, but males are not. The population density can be as high as 10 squirrels per hectare in favorable conditions.

Northern flying squirrels emit a soft low chirp, and they cluck when distressed. They also use scent and touch to communicate with one another.

They have excellent senses of hearing, smell, vision, and touch.

Glaucomys sabrinus has a characteristic squirrel diet. They eat nuts, acorns, fungi, and lichens, supplemented by fruits, buds, sap and the occasional insect and bird egg. Northern flying squirrels diverge from many squirrels in that lichens and fungi are a large portion of the diet and are not just supplements. It is thought that northern flying squirrels hoard food for the winter, though this has not been confirmed.

The main predators of northern flying squirrels are owls, hawks, martens, weasels, coyotes, and the domestic cat. They avoid predation mainly by being active at night and through their vigilance and agility in the trees.

Glaucomys sabrinus may be important in the dispersal of spores of mycorrhizal fungi. Northern flying squirrels may also be important in the dispersal of conifer cones, though some wonder if their activity actually impedes forest reproduction through their predation on seeds.

Northern flying squirrels sometimes select den sites in houses and barns, which is undesireable due to the noisy activity at night and the litter from nests and seed caches. Northern flying squirrels can also cause problems for professional trappers in the winter, as the squirrels enter traps set for martens and minks.

The subspecies Glaucomys sabrinus coloratus and G. s. fuscus are threatened populations in the Appalachians. Glaucomys sabrinus coloratus, North Carolina flying squirrels were designated as endangered in 1985. Between the 1880's and the 1920's, 500,000 acres of forest supporting the two subspecies were reduced by timbering to 200 acres. Conservationists are concerned that further habitat destruction, fragmentation, and pollution will eliminate the small and vulnerable islands of high elevation habitats. The plan being implemented through the U.S. Fish and Wildlife office is the following: 1) determine the exact distribution of the two subspecies 2) protect areas with suitable habitat 3) explore the ecology of the two subspecies 4) test the response to various habitat modifications, concentrating on enhancement measures and compatible timber harvest methods. Some argue that many other populations of subspecies are also endangered, but none have been listed as of yet.

The wing-loading coefficient of northern flying squirrels is about 50 Newtons/square meter, 2-3 times that of most bats. An average 'flight' of G. sabrinus is 20 meters, though flights as long as 90 meters have been recorded. Northern flying squirrels have also been seen making full semi-circles in a single flight.