Gray and Red Squirrels do not retreat into deep, months-long hibernation when snow blankets the landscape. They remain active throughout the winter, requiring immediate, reliable shelters to survive sudden temperature drops and heavy snowfall. Their response to winter weather is purely behavioral, involving a quick dash to shelter to conserve energy needed for later foraging.
Immediate Winter Shelters
When a winter storm hits, squirrels seek refuge in one of two arboreal dwellings: the natural tree cavity or the constructed nest, known as a drey. The tree cavity, often a hollow space formed by wood rot or an old woodpecker hole, is the preferred winter home. These dens offer superior protection from wind and moisture, providing the most stable and warmest environment. Squirrels line these cavities with soft materials like leaves, moss, and shredded bark to maximize insulation.
If a suitable tree cavity is unavailable, the squirrel retreats to a drey, a round nest built high in the branches near the trunk. A winter drey is a meticulously engineered structure, typically the size of a football, constructed from an interwoven frame of twigs. This frame is packed with layers of dry leaves, grass, and bark strips, creating a robust and well-insulated shelter. Research shows the temperature inside a drey can be significantly warmer than the air temperature outside.
Winter Activity and Energy Conservation
The active winter lifestyle requires tree squirrels to balance the need for warmth with the need for food. Unlike true hibernators, which enter a prolonged state of deep metabolic shutdown, squirrels employ a survival strategy called torpor. Torpor is a temporary state of reduced metabolic activity where body temperature, heart rate, and breathing slow down to conserve energy.
A squirrel may enter torpor for several hours or days, particularly during severe storms or extreme cold. This metabolic slowdown minimizes the use of stored fat reserves, but it is not a deep, involuntary sleep. They can wake easily to forage once the worst of the weather passes, which is why they are often seen even on cold, sunny winter days. This ability to quickly emerge distinguishes their strategy from the long-term hibernation of animals like groundhogs.
Finding Food Under Snow
A blanket of snow poses a significant challenge to a squirrel’s primary food source: the caches of nuts and seeds buried during the fall. To locate these hidden reserves, squirrels rely on acute spatial memory and their sense of smell. Spatial memory is the primary tool, allowing the squirrel to recall the precise location of thousands of caches relative to nearby landmarks. This cognitive map guides the squirrel to the correct general area, even when visual cues are obscured by snow.
Once in the correct location, their keen sense of smell takes over, enabling them to detect the scent of buried food through several inches of snow. This olfactory detection is important for pinpointing the exact spot for excavation. The squirrel then digs a tunnel or “midden” through the snow layer to retrieve the cache. Retrieving up to 95% of hidden nuts demonstrates the effectiveness of this combined sensory strategy for winter survival.