Fig. 91. Northern flying squirrel (Glaucomys sabrinus), probably from near Seattle, in Woodland Park Zoo, Seattle, Washington, January 28, 1941. (Fish and Wildlife Service photo by Victor B. [Scheffer], No. 1137.)
Description.—The northern flying squirrel is slightly smaller than the red squirrel (Tamiasciurus). The head and body measure about 7 inches and the tail about 5 inches. The most distinctive feature is the loose fold of skin that stretches from the wrist of the foreleg to the ankle of the hind leg. The fur is extremely soft and plushlike. It is not separated into guard hair and underfur, and because all hairs are of approximately the same length, the fur appears extremely sleek. The fur of the tail is of the same texture as that on the body but is dorso-ventrally compressed. The eyes are large and dark. The color of the upper parts varies from reddish brown in some races to brownish gray in others. The underparts are buffy gray.
Flying squirrels range over the forested parts of North America from Guatemala to Alaska and northern Canada and from the Atlantic to the Pacific. A closely related genus (Pteromys) occurs in Europe. Two species are found in North America. The small volans ranges in eastern United States, Mexico, and Guatemala, while the larger sabrinus occurs in parts of the western United States, most of Canada, and central Alaska. Near the Great Lakes the two species occur in the same area, probably in different habitats.
[Howell] (1918: 16) recognized 18 subspecies of sabrinus, five of which were recorded in the state of Washington. One of these (olympicus) proves to be a synonym of an earlier-named subspecies but another form (bangsi), not recorded for Washington by [Howell], has been found in the Blue Mountains in the southeastern corner of the state ([Taylor] and [Shaw], 1929: 18).
Flying squirrels are strictly arboreal and occur only in woods and forests. They prefer areas where trees grow close together and to considerable heights. Older woods with dead stubs and hollow trees are preferred. They occasionally invade attics of cabins and other habitations of man. The old Forestry Building on the University of Washington Campus, later the home of the Washington State Museum, was inhabited by flying squirrels for many years. Several specimens preserved in the Museum prove the poor judgment of the animal in choosing a natural history museum as a home.
Relatively little is known of the detailed habits of Glaucomys sabrinus although the life history of the eastern Glaucomys volans has been described. Flying squirrels are active all winter, even in the high mountains. They are often caught in traps set for fur bearers and, where trapping is an important means of livelihood, they are serious pests. Flying squirrels do not actually fly but only glide through the air. The loose fold of fur between their limbs is stretched by extending the legs. With it the flying squirrel is able to sail 50 yards or more. The flat tail serves as a rudder and allows the squirrel to change direction while in flight. Glides end with an upward swoop, allowing the squirrel to alight, head upwards, on a tree trunk slightly lower than their starting point.
Unlike other members of the squirrel family, flying squirrels are completely nocturnal. They are seen in the daytime only when frightened from their retreats. Homes consist principally of old woodpecker holes or other cavities in trees. They are said to build outside nests, similar to those of tree squirrels, but I have found none of these in Washington. The animals can be frightened from their holes by pounding on the bases of trees in which their nests are situated. Certain holes seem to be preferred nesting places. Near Cottage Lake, King County, two flying squirrels were taken from a woodpecker hole in succeeding years. [Cowan] (1936B: 58) discovered remains of 14 nests of flying squirrels in a single hollow tree near Alta Lake, British Columbia. According to [Cowan], hollow trees are used in winter but the young are born in outside nests of shredded bark and lichens. The young usually number 3 and are born in May and June.