Many people wonder if squirrels truly hibernate during colder months. The answer is more nuanced, as squirrel winter behaviors vary significantly. While some species enter a deep, prolonged sleep, many common types employ different strategies to endure the winter season.
Not True Hibernators
Most common squirrels, such as grey and red squirrels, do not truly hibernate. True hibernation involves a sustained, deep sleep where an animal’s body temperature, heart rate, and metabolism drop dramatically for weeks or months, making them difficult to rouse. Instead, these squirrels may enter torpor, a temporary reduction in metabolic activity, body temperature, and heart rate, which conserves energy during cold spells.
Unlike true hibernators, squirrels in torpor can wake up quickly to forage or respond to threats. This state can last for a few hours, several days, or even a few weeks, depending on environmental conditions. Squirrels may enter torpor when temperatures drop below approximately 50 degrees Fahrenheit. This physiological adjustment is a flexible energy-saving mechanism, distinct from the long-term shutdown seen in true hibernation.
How Squirrels Survive Winter
Squirrels that do not truly hibernate rely on behavioral adaptations to survive the winter. A primary strategy is food caching, where they bury or store nuts and seeds. They often use “scatter hoarding,” distributing food in numerous shallow holes across their territory, which they later locate using memory and a keen sense of smell. This ensures a readily available food supply when natural resources become scarce.
Denning behavior also plays a significant role in winter survival. Tree squirrels construct nests, called dreys, from twigs, leaves, and moss, often high in tree branches or within tree cavities. These insulated dens provide shelter from harsh weather, with the interior of a well-built drey being significantly warmer than the outside air. For additional warmth, multiple squirrels may huddle together in a single den. They also build up fat reserves by eating more in the fall, which provides energy and insulation.
Species-Specific Winter Behaviors
Whether squirrels hibernate depends on the specific species. While most common tree squirrels, like Eastern Grey and Red Squirrels, remain active year-round and do not hibernate, many ground squirrel species are true hibernators. Ground squirrels, such as the Arctic ground squirrel, spend months in a deep sleep within underground burrows, significantly slowing their heart rate and metabolism. The Arctic ground squirrel’s body temperature can even drop below freezing during hibernation.
Flying squirrels, another tree squirrel type, also do not hibernate. They remain active throughout winter but adapt their behavior to colder conditions. These nocturnal creatures often form communal nests, huddling in groups of up to 19 individuals in tree cavities or abandoned nests to conserve body heat. They rely on stored food from the fall and forage for tree seeds, nuts, and fungi during milder periods.