hibernating

Hibernating refers to a state of prolonged, energy-conserving inactivity used by some endothermic animals during winter. In true hibernation, the animal's metabolic rate falls dramatically, body temperature drops toward the surrounding environment (often to near ambient temperatures), and physiological processes such as heart rate and breathing slow considerably. Hibernation is distinct from daily torpor and from estivation, though all are forms of reduced metabolic activity.

During hibernation, the animal relies on stored body fat for energy. The winter period is partitioned into bouts of deep torpor with occasional arousals, during which the animal briefly returns to a warmer, more active state before resuming hibernation. Arousals may serve purposes such as waste clearance, immune surveillance, or rehydration. Because metabolic demands are so low, hibernating animals can survive months when food is scarce.

Hibernation behavior and physiology vary by species. True hibernation is seen in many small mammals such as ground squirrels, bats, and some hedgehogs and marmots. These animals typically seek sheltered dens called hibernacula, where environmental conditions are stable. The timing of hibernation is influenced by seasonal cues such as daylight and temperature, and by the animal’s fat reserves and feeding prior to winter.

The term hibernation is sometimes used loosely to describe extended sleep in animals, including reduced nocturnal activity in non-hibernating species. In humans, research into therapeutic hypothermia and related methods draws on principles of hibernation to extend metabolic protection in medical or spaceflight contexts, but true seasonal hibernation is not known to occur in humans.