The eastern gray squirrel, the type commonly seen in trees, does not hibernate during the winter, but the ground squirrel does hibernate in the winter. Both types of squirrel are common in North America, with the main difference being that the ground squirrel does not make its nests in trees, but creates burrows in the ground.
Gray squirrels are active throughout the winter. These squirrels store food in little pockets all around the forest floor and within trees to help sustain them through winter when food is scarce. Gray squirrels will hunker down in their nests for warmth and use the act of shivering to raise their body temperature.
Ground squirrels begin fattening up in the summer. When winter sets in, the ground squirrel will burrow down and sleep for 5 to 7 months. These squirrels awaken every few weeks, but quickly return to a state of hibernation.