The familiar North American tree squirrel, such as the Eastern Gray squirrel, does not disappear completely when winter arrives. Unlike many other small mammals that enter a state of deep, sustained hibernation, tree squirrels remain active throughout the cold season. Their survival strategy is centered on meticulous preparation and an ability to conserve energy while still making periodic foraging trips.
The Winter Activity Level
Tree squirrels are not true hibernators, meaning they do not enter the profound, weeks-long physiological shutdown seen in animals like groundhogs. Instead, they operate on a strategy of short-term energy conservation known as torpor. This state involves a temporary and limited reduction in the squirrel’s metabolic rate, heart rate, and core body temperature.
Torpor is typically used during the harshest periods of winter weather, such as intense cold snaps or heavy snowstorms. It allows the animal to conserve the stored energy needed to maintain its normal body temperature. Unlike a true hibernator, the squirrel can be easily roused from torpor within a few hours to find food or respond to a threat.
The decision to use torpor is opportunistic and based heavily on external conditions, lasting only for a few hours or a few days at a time. This intermittent rest allows them to minimize energy expenditure when foraging is difficult or dangerous. When the weather moderates, the squirrel will become active again to access its hidden food supplies.
Shelter and Nesting Locations
The primary winter residence for a tree squirrel is a structure called a drey, which is a round, messy-looking nest high in a tree canopy. Dreys are usually constructed from interwoven sticks and leaves, often built in the forks of branches or close to the trunk for stability.
These nests are engineered for insulation, featuring a thick exterior layer and a fine interior lining of soft materials like moss, grass, and shredded bark. This layered construction provides a significant thermal advantage. A well-insulated winter drey can be much warmer inside than the outside air temperature.
When available, squirrels prefer the greater protection of a tree cavity, such as a hollowed-out section of a trunk or a hole excavated by a woodpecker. These natural dens offer superior protection from wind and moisture compared to a drey. Multiple squirrels may share a nest during the coldest periods to maximize warmth through collective body heat.
Foraging and Food Storage
The ability to survive winter hinges on the massive amount of food cached during the preceding fall months. Tree squirrels primarily employ a strategy known as scatter-hoarding, which involves burying individual food items, mostly nuts and acorns, across a wide territory.
This method minimizes the risk of losing the entire winter supply to a single theft, unlike the larder-hoarding strategy used by some other species. To retrieve these scattered resources, gray squirrels rely heavily on a detailed spatial memory combined with a keen sense of smell.
The squirrel’s saliva, deposited on the nut before burial, may also act as an olfactory signpost, helping the animal locate the cache under snow and frozen ground. Over the winter, a successful scatter-hoarder will recover between 40 to 80 percent of its hundreds of caches. These recovered nuts provide the necessary calories for the squirrel to sustain brief foraging trips and maintain its body temperature until spring.