Part of the mosaic must be old coniferous forest with den trees containing witches' brooms, woodpecker cavities, and natural cavities for nesting sites. Riparian zones provide excellent habitat in all coniferous forest associations. The female can breed before 11 months of age and give birth at about 1 year of age. Gestation requires about 37 days, so the young are born from May to early July. One litter of two per year is probably the usual case for Alaska, but they are known to have litters ranging from one to six in other parts of their range.
Development is slow in comparison with other mammals of similar size.
Their eyes open at about 25 days, and they nurse for about 60 to 70 days. By day 240, the young are fully grown and cannot be distinguished from adults by body measurements and fur characteristics. Mortality rate for flying squirrels 1 and 2 years old is about 50 percent, and few live past 4 years of age. Complete population turnover can occur by the third year. Individual flying squirrels nest in tree cavities, witches' brooms, and drays.