Hibernation is a survival strategy employed by certain animals to endure environmental adversity. This physiological state allows creatures to conserve energy when food sources become scarce and temperatures plummet, typically during winter months. Instead of migrating or constantly searching for sustenance, these animals enter a prolonged period of inactivity. This adaptation involves significant changes within the animal’s body, enabling them to survive challenging conditions until more favorable times return.
Animals That Hibernate
Many animal species engage in hibernation to overcome winter’s challenges. Groundhogs, also known as woodchucks, spend up to five months in their burrows. During this time, their body temperature drops considerably, and their heart rate slows dramatically, allowing them to rely on stored fat reserves. Marmots also hibernate in underground burrows for extended periods, sometimes as long as eight months.
Arctic ground squirrels hibernate for seven to eight months, with their body temperature dropping to below freezing, sometimes as low as 27°F (-3°C). Bats often seek cool, constant-temperature roosts like caves or abandoned mines for winter. They prepare for hibernation by consuming large amounts of insects in the fall to build up fat reserves.
Some hamster species also hibernate, though their patterns can vary. Hedgehogs, too, enter a state of torpor during winter, preparing by accumulating significant fat reserves.
The Biology of Hibernation
Hibernation involves physiological transformation, allowing animals to drastically reduce their energy expenditure. A key change is a significant drop in body temperature, which can fall to near ambient levels in some species, such as the Arctic ground squirrel, whose core body temperature can reach -2.9°C (26.8°F). This cooling is accompanied by a dramatic reduction in metabolic rate, sometimes by as much as 95%. The heart rate also slows considerably; for instance, a groundhog’s heart rate can plummet from around 80 beats per minute to just 5-10 beats per minute.
Breathing becomes shallow and infrequent during hibernation, with some bats taking only a few breaths per minute. These physiological changes reduce the animal’s need for calories, allowing them to survive on fat reserves accumulated before hibernation. Animals become hyperphagic, eating large amounts of food to store energy as fat. Brown fat provides quick bursts of energy to warm vital organs during periodic arousals.
Hibernation differs from other forms of inactivity like torpor and brumation. Torpor is a shorter-term state of reduced metabolic activity, often lasting only a few hours or days, and can occur at any time of year. Animals like some bats and chipmunks may enter daily torpor to conserve energy between foraging bouts. Brumation is a dormant state primarily seen in ectothermic (cold-blooded) animals such as reptiles and amphibians. Unlike hibernators, brumating animals cannot control their body temperature internally and may periodically wake to drink water.