As colder weather arrives, many people wonder how these active rodents manage to survive the winter months. Their strategies involve more than just finding food; they encompass unique physiological adaptations, carefully constructed shelters, and clever food management.
Winter Activity and Torpor
Tree squirrels, such as the common gray squirrel, do not hibernate in the traditional sense. Unlike animals that enter a deep, prolonged sleep, tree squirrels remain active throughout winter, though their activity levels decrease. Instead of true hibernation, they employ a survival mechanism called torpor. Torpor is a state of reduced metabolic activity where an animal’s heart rate, breathing, and body temperature drop, conserving energy during extreme cold or food scarcity. Squirrels can enter and exit torpor easily for short periods, from a few hours to several days, especially when temperatures fall below 50 degrees Fahrenheit, waking to forage before returning to a torpid state.
Shelter and Keeping Warm
To endure the cold, squirrels rely on well-insulated shelters. They primarily use nests called dreys, built high in trees, often 20 to 45 feet off the ground, within forks of branches or close to the trunk. Dreys are spherical structures, about 12 inches in diameter, constructed from interwoven twigs, dry leaves, and grass, with an inner core lined with softer materials like moss, feathers, shredded bark, or pine needles, creating a warm, dry haven. Squirrels also utilize natural tree cavities, which offer greater protection from wind and snow, adapting existing holes for warmth. In severe weather, multiple squirrels may share a drey or cavity to benefit from communal body heat, and their thick winter fur provides insulation.
Food Storage and Foraging
Preparing for winter’s food scarcity is a primary concern for squirrels. They spend autumn gathering nuts, seeds, and other edibles, a behavior known as caching. Most tree squirrels, like the gray squirrel, engage in “scatter hoarding,” burying individual food items in numerous shallow holes across their territory. This strategy ensures that if one cache is discovered, not all their food supply is lost. When winter arrives, squirrels retrieve their buried stores using memory and a keen sense of smell, detecting nuts even under a foot of snow. Studies suggest they recover a high percentage of buried nuts, between 40% and 95%, with unrecovered nuts often germinating and contributing to forest regeneration.
Different Squirrel Survival Strategies
The term “squirrel” encompasses various species, and their winter survival strategies differ significantly. While tree squirrels primarily rely on torpor and active foraging, ground squirrels exhibit true hibernation. Ground squirrels, such as the 13-lined or Arctic ground squirrel, enter a much deeper state of dormancy, with body temperature, heart rate, and metabolism dropping for extended periods, sometimes for months. They rely on fat reserves built up during warmer months. This distinction is important because while you might see a tree squirrel out on a mild winter day, a ground squirrel will likely remain hidden in its underground burrow until spring.