The fox squirrel (Sciurus niger) is the largest species of tree squirrel native to North America. It is recognizable by its robust size and variable coat, which often features buff, orange, or rufous coloration on its underside. These animals are found across the eastern and central United States, typically inhabiting open forests, woodlots, and urban environments with mature trees. Fox squirrels do not hibernate in the winter; instead, they employ behavioral and physiological strategies to survive the coldest months.
Winter Dormancy vs. True Hibernation
Fox squirrels remain active throughout the winter, setting them apart from true hibernators like groundhogs or marmots. True hibernation is a profound, extended state of deep sleep lasting for months. During hibernation, an animal’s heart rate, breathing, and body temperature drop dramatically to near-ambient levels. The animal relies solely on stored body fat for energy without waking to eat or excrete waste.
The state a fox squirrel enters during severe cold snaps is better described as a deep sleep or short-term torpor. This is a much milder form of dormancy, involving only a slight, temporary reduction in the animal’s metabolic rate and body temperature. Fox squirrels are homeotherms, meaning they maintain a relatively constant body temperature. They wake frequently—sometimes every few days—to feed on cached food or relieve themselves. Constant access to a food supply is a necessity for their survival.
Preparing for Winter: Food Caching and Foraging
Since they do not enter a long-term dormant state, a reliable food source is paramount for winter survival. In the fall, they gather food to build up internal fat reserves and external caches. They focus on high-energy, high-fat items like acorns, hickory nuts, and walnuts, which they test for quality before storage.
Fox squirrels are known as scatter-hoarders, burying individual food items in shallow holes across a wide territory. This strategy differs significantly from larder-hoarding, which involves creating a single, large food pile. Their ability to relocate these hidden caches, even under a layer of snow, relies on excellent spatial memory combined with a highly developed sense of smell. This behavior ensures they have numerous, accessible food sources when they awaken during the winter months.
Staying Warm: Shelter and Nesting Habits
To conserve the energy they gain from their cached food, fox squirrels utilize specialized structures to shield themselves from the harsh winter weather. Their preferred shelter is a natural tree cavity, or den, found within the trunk or large limbs of a mature tree, which offers the best insulation. These tree dens are often used year after year and provide superior protection from wind and moisture.
When natural tree cavities are scarce, they construct large, spherical nests called dreys high in the branches. Dreys are built using a dense framework of twigs and leaves, then carefully lined with soft materials like moss and dried grass to create an insulated inner chamber. During periods of extreme cold, multiple fox squirrels may engage in communal nesting, huddling together to share body heat and maximize energy conservation.