Courtship of flying squirrels 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. Usually, 2 to 4 young are born, though litters as small as 1 and as large as 6 have been recorded. Flying squirrels breed in the first summer after their birth.
The Northern Flying Squirrel eats nuts, acorns, fungi, and lichens, supplemented by fruits, buds, sap and the occasional insect and bird egg. Northern Flying Squirrels diverge 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 confirmed.