The mating season begins late March and early April. It is common for the male to be driven off by their mate before their young are born since the female northern flying squirrel is territorial, whereas the male is not (Mammath and Mulheisen, 1996). At night the adults may feed and play together, but there is no evidence that the males ever get to be with their offspring. The squirrels give birth in late April to June, and one litter is born a year. The average litter size is three, but the range is from as little as one to as many as six (Malamuth and Mulheisen 1996). The gestation period is 37-42 days, and the newborns are naked, deaf, blind, hairless and weigh about 5-6 grams. In about a month they have grown some fur, and may weigh four times as much as when they were born. At about nine weeks they are weaned and become more and more independent. By the twelfth week they try gliding. At four months they become good gliders and are able to take care of themselves.
Northern Flying Squirrels moult once a year in autumn. They are clean animals and spend part of their day grooming. Their active period is pretty short, just a couple of hours after sunset and the last hour or so before sunrise (Savage, 1981). They have a call that is typical for squirrels a “chuck chuck,” but sometimes they chirp notes like a bird. Their main predator is the Great Horned Owl, but the marten, lynx, bobcat, weasel, fox, ermine, and fisher are also their predators (Woods, 1980).