Northern flying squirrels weigh between 75 and 140 grams, and range from 275 to 342 mm in length. They have 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). Northern flying squirrels have large black eyes, which they use for nighttime activity. Southern flying squirrels, which appear similar to 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.
Northern flying squirrels range 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. Small populations live in the mountains in other parts of the United States, including the southern Appalachian Mountains, the Black Hills, and the Sierra Nevada.
Usually found in areas with mostly conifers, northern flying squirrels can also be relatively abundant in deciduous and mixed coniferous/deciduous forests. Northern flying squirrels have been found in diverse areas including regions made up of spruce, fir, and mixed hemlocks, in beech maple forests, and in areas of white spruce and birch with interspersed aspen groves. Northern flying squirrels often nest 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.
Little 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. Mating occurs in early spring and is followed by a pregnancy 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.
Northern flying squirrels are clumsy on the ground, but can glide gracefully up to 48 m (160 feet) from tree to tree. Northern flying squirrels sometimes share nests and may live in groups of up to 8 adults and juveniles. Individual northern flying squirrels gather into single-sex groups for warmth during the winter. Coming out only at night, 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 (0.008 square kilometers) to 31 hectares (0.31 square kilometers). Female northern flying squirrels are territorial, but males are not. Up to 10 squirrels can be found per hectare when there is plenty of food and shelter.
Northern flying squirrels give 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.
Northern flying squirrels have a typical squirrel diet. They eat nuts, acorns, fungi, and lichens, supplemented by fruits, buds, sap and the occasional insect and bird egg. Northern flying squirrels differ 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 proven.
The main predators of northern flying squirrels are owls, hawks, martens, weasels, coyotes, and the domestic cat. They avoid predators mainly by being active at night and through their alertness and agility in the trees.
Northern flying squirrels may be important for spreading spores of fungi. Northern flying squirrels may also be important in the spreading conifer cones, though some wonder if their activity actually hurts forest growth because they feed on the 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 seeds. Northern flying squirrels can also cause problems for professional trappers in the winter, as the squirrels enter traps set for martens and minks.
There are no known direct positive effects of northern flying squirrels on humans. Because they are may disperse seeds and spores and are prey to a variety of predators, they help maintain a thriving ecosystem.
Two types of northern flying squirrels, North Carolina northern flying squirrels and West Virginia northern flying squirrels, are threatened populations in the Appalachians. North Carolina northern flying squirrels were listed as endangered in 1985. Between the 1880's and the 1920's, 500,000 acres of forest where these two type of squirrels live were reduced by logging to 200 acres. Conservationists are concerned that further habitat destruction and pollution will wipe out what remains of vulnerable mountain habitats. The plan being carried out through the U.S. Fish and Wildlife office is the following: 1) figure out the exact range of these two types of squirrel 2) protect areas with suitable habitat 3) explore the ecology of the squirrels 4) test the response to various habitat changes, focusing on how to make the habitat better and harvest trees in a way that won't disturb the squirrels. Some argue that many other populations of northern flying squirrels are also endangered, but none have been listed as of yet.
Tanya Dewey (editor), University of Michigan-Ann Arbor, George Hammond (editor), Animal Diversity Web Staff.
Allison Poor (editor), University of Michigan-Ann Arbor.
Eldad Malamuth (author), University of Michigan-Ann Arbor, Michael Mulheisen (author), University of Michigan-Ann Arbor.
Annapolis field office of the U.S. Fish and Wildlife Office and the Northern Flying Squirrel Recovery Team. 1990. Appalachian Northern Flying Squirrels Recovery Plan. Annapolis, U.S.A.
Baker, Rollin H. 1983. Michigan Mammals. Michigan State University Press, East Lansing, pg 236-243.
Kurta, Allen. 1985. Mammals of the Great Lake Region. University of Michigan Press, Ann Arbor, pg 131-134
Wells-Gosling, Nancy. 1985. Flying Squirrels. Smithsonian Institution Press. Washington, D.C.
Wells-Gosling, Nancy, and Heaney, Lawrence R. 1984. Glaucomys sabrinus. Mammalian Species No. 229. American Society of Mammalogists. North Hampton, Ma.