Habitat
Prefers coniferous and mixed forest, but will utilize deciduous woods and riparian woods. Optimal conditions have been reported as cool, moist, mature forest with abundant standing and down snags. Often most abundant near surface water; that is, swamps or streams (Heaney, in Wilson and Ruff 1999). In the Oregon Cascades, Rosenberg and Anthony (1992) concluded that flying squirrels are habitat generalists and are not more abundant in old growth than in younger, second-growth stands. Occupies tree cavities, leaf nests, underground burrows; uses large number in alternate den sites in Alaska (Austin et al., no date). See Payne et al. (1989) for habitat characteristics of endangered Appalachian populations. Prefers cavities in mature trees as den sites. In winter in British Columbia, squirrels appeared to select nest trees more for suitable nest sites than for tree size: diameter at breast height was 16.7-79.0 cm, age was 42-174 years, and height was 11.2-32.7 m (Cotton and Parker 2000). Small outside twig nests sometimes are used for den sites. Sometimes uses bluebird boxes.
Ecology
Highly social, especially in winter when nests may be shared. Apparently lives in family groups of adults and juveniles.
In western Oregon, population density was 0-0.24/ha (mean 0.12) in second growth forest and 0.52-1.28/ha (mean 0.85) in old-growth forest (Witt 1992). Density averaged 2.0-2.3/ha in Douglas-fir habitats in western Oregon (Rosenberg and Anthony 1992). In Utah, density was 0.2-1.8/ha in POPULUS-dominated forest, 1.2-5.8/ha in ABIES-dominated forest, and 0.2-2.1/ha in PICEA-dominated forest (see Witt 1992). Sciurid mycophagy may play an important role in forest ecology (Maser and Maser 1988).
Reproduction
Breeding season: February-May; July. Gestation lasts 37-42 days. One or two litters of 2-6 young (average 4-5) are born March-early July, and late August to early September (apparently one litter in spring or summer in the southern Appalachians). Weaned at about 2 months. Sexually mature at 6-12 months.