(Glaucomys sabrinus fuscus)
This species is larger than G. volans, with a browner dorsal pelage, distinguished by the belly hairs being slate-colored at the bases,the coat is dense, soft and the sides grayish-brown, sometimes washed with cinnamon. The tail is broad, horizontally flattened, and there are membranes (patagia) between the fore and hind legs. The eyes are prominent, large and blackish. The total length is 11-12 in. (290 mm), and weight 4-6.5 ounces. This species usually lives in small family groups in nests in tree holes, and old bird nests. One litter of 2-4 young are born in May and June each year. They are nocturnal, usually active even in the severest winter weather. The voice is high-pitched insect-like chirps. They are on the verge of extirpation in Virginia. There has been a major push since being declared endangered leading to nest box placement in 10 counties of western and southwestern Virginia.
G. sabrinus fuscus has been confirmed in Highland and Montgomery Counties from capture data. South of Pennsylvania, this species occurs in small, isolated, relict populations at high altitudes. This subspecies is typically found in conifer-hardwood ecotones or mosaics consisting of mature beech, yellow birch, sugar maple, hemlock, and black cherry associated with red spruce and balsam or Fraser fir.. This species often lives near streams and rivers.
In the winter, this species feeds from caches in crevices, crotches of trees. They can survive on a diet of lichens and fungi, and may thus be less dependent on seeds and nuts than G. volans. It spends more time foraging on ground than the southern flying squirrel.