The majority of ground and tree squirrels are diurnal, meaning they are active during the day and sleep at night. Flying squirrels, however, tend to be nocturnal and are active at night.

The grey squirrel is one of the most common squirrels to North America and is diurnal. It has a lifespan of one to two years in the wild, but some have been known to last 10 years. Grey squirrels do not hibernate in the winter but do build nests to go to when weather is especially inclement.

Flying squirrels glide between trees at distances up to 300 feet. They tend to be nocturnal because they are less susceptible to predator attacks at night.