Hibernation is one of the most extreme survival strategies in nature. It’s not just deep sleep. A truly hibernating animal slows almost every body function down to a tiny fraction of normal - its heart rate, breathing, body temperature, and metabolism all crash to levels that would kill almost any non-hibernating animal.
Ground squirrels are the extreme example. A waking ground squirrel has a heart rate around 200 beats per minute. Hibernating, that drops to 5 beats per minute. Its body temperature falls from 37°C down to nearly freezing - sometimes 1°C. Its breathing slows to maybe one breath every few minutes. The animal looks essentially dead. It can stay this way for weeks at a time, with brief warmer interludes, all winter long.
Bears do something a bit different - their body temperature drops only about 10°C, and they can wake up much more easily. Strictly speaking, scientists sometimes call bears’ winter sleep “torpor” rather than true hibernation. Either way, the strategy is the same: dramatically lower energy needs during a season when food is scarce, by basically pausing the body until conditions improve. When spring returns, hibernators slowly warm back up and resume their normal lives - a real-life Sleeping Beauty trick repeated every year.
