Squirrels are a common sight, busily scampering and gathering. As colder months arrive, many wonder if these active rodents hibernate. The answer is not a simple yes or no, as the term “squirrel” encompasses diverse species with varied winter behaviors.
Not All Squirrels Are The Same
The squirrel family, Sciuridae, includes many species with differing winter survival strategies. The distinction lies between ground squirrels and tree squirrels.
Ground squirrels, such as marmots, chipmunks, and prairie dogs, are true hibernators. They spend winter months in a prolonged state of inactivity underground.
Tree squirrels, like grey and red squirrels, do not truly hibernate. These species remain active throughout winter, though their activity may decrease during the harshest weather. This difference in behavior helps explain how various squirrels cope with cold temperatures and limited food.
Winter Survival Strategies
Tree squirrels employ several strategies to survive winter. A primary method is food caching, where they bury nuts and seeds in autumn for later retrieval. Grey squirrels, for example, “scatter hoard” by burying individual food items in many locations. They possess spatial memory, allowing them to recover 40-80% of their buried caches.
Beyond food storage, tree squirrels rely on well-insulated nests, known as dreys, or seek refuge in tree cavities. Dreys, built high in trees from twigs and leaves, provide insulation against cold and wind. During severe cold, squirrels may huddle in these nests to share body warmth and conserve energy. They also grow a thicker fur coat in winter for natural insulation.
Tree squirrels engage in periods of torpor, a state different from true hibernation. This involves a temporary reduction in metabolic activity and body temperature, conserving energy during short cold snaps or food scarcity. While in torpor, they can be roused and periodically wake to access food caches.
Hibernation Versus Torpor
Hibernation and torpor both describe states of reduced activity and metabolism, but they are distinct physiological processes. True hibernation is a prolonged state of inactivity, lasting weeks or months, characterized by a significant drop in body temperature, heart rate, and metabolic rate. For example, a hibernating ground squirrel’s heart rate can decrease to just a few beats per minute, and their body temperature can fall to 4-8°C. Metabolic rates can be suppressed by over 90% of their normal resting rate. Animals in this state periodically awaken before re-entering torpor.
Torpor is a shorter, less extreme reduction in metabolic activity. It lasts from a few hours to several days, often a response to daily temperature fluctuations or temporary food shortages. While body temperature and metabolic rate decrease during torpor, the reduction is not as profound or sustained as in hibernation. Animals in torpor remain more responsive to external stimuli and wake more frequently, enabling them to forage when conditions improve.