Lots of animals hibernate, like frogs, mice, squirrels, hedgehogs, and even skunks! You might think that they hibernate—a.k.a. take cover in a warm, sheltered environment during the long, cold winter months—to simply sleep away the season and avoid extremely low temperatures. But there’s actually a lot more to it than that.
Take bears, for example. While it’s true that bears don’t need to eat or drink (or even urinate or defecate!) while they hibernate, they actually aren’t asleep the whole time. Hibernating bears will, on occasion, leave their dens—particularly when the dens are damaged or flooded. And even while they’re still in the den, hibernating bears will go through a lot of posture changes and movements, and will even get up and move around from time to time.
For most animals, the act of hibernation isn’t considered sleep, per se, because the physiological changes that they go through vary drastically from a normal sleep routine. For instance, during hibernation, animals have reduced heart rates and blood flow, and they survive without eating because their bodies drastically reduce their metabolism. Some animals may even experience a temperature drop by as much as 63 degrees Fahrenheit.
So if it’s not about catching up on some much-needed zzz’s or avoiding freezing weather, then why do animals hibernate? It’s actually a survival tactic. During cold winters, it’s harder for crops to grow, so food is scarce. Animals’ bodies adapted to hibernate and conserve energy so they would need less grub to live.