As we pile on layers, many other mammal species, and even some fish, are hanging out in hibernation until springtime. A season-long slumber is a practical means of energy conservation for hundreds of thousands of creatures, from lizards to bears, who otherwise might struggle to survive the cold months. Food sources are much scarcer in winter, and competition for food taxes the ecosystem. So, by necessity, animals take to dens, caves or tree holes to sleep away winter on low-energy mode. This enables them to stay in a deep sleep and wake up trimmer, though weaker, than when they started hibernating.
To hibernate, most animals gorge on excessive amounts of food beforehand; they store fat deposits that will slowly burn off as energy. (Some smaller animals will instead store food in their den so that they can periodically wake to eat in a process referred to as “food caching”.) All hibernating animals are able to survive like this becasue their bodies enter a slowed-down metabolic state, marked by changes including decreased heart rates and breathing rates. This way, they burn less energy and require little-to-no food intake to stay alive.
Slowed-down metabolic rates vary among species. Woodchucks’ heartrate, for example, drops from 80 beats per minute to just four or five, while their body temperate plummets as much as 60 degrees below the usual level. Some animals, however, aren't "true" hibernators. Bears, for instance, experience “torpor” instead, meaning they're easier to wake up and their body temperature drops less dramatically, due to their large size. Many small animals practice daily torpor, and not just in cold months: Bats, hummingbirds and rodents, for example, spend only the active part of each day in a deep slumber. Daily torpor differs from normal sleep metabolism and body temperature drops so significantly.
Haven't gotten your fill of hibernation facts? Well, here are some more:
It's good to be the queen
Many species of bees and wasps die out each winter, while one sole survivor carries on the family name: the HBIC. After all the males die, the queen finds a small hole in the ground to take residence for half the year. She then emerges to start her empire anew.
Frogs are the future
Many wood frogs actually stop breathing during hibernation; they crawl into logs or hide under rocks and freeze entirely. Their blood crystalizes, their heart stops and, when everything thaws out, they jump right back to life. Anyone chasing cryogenic sleep solutions should take note.
Bears know how to “back it up”
How do some animals last so long without having to use the bathroom? Well, for starters, keep in mind that most of them aren’t consuming more food; they’re just burning off fat deposits. And many can recycle any produced urea as amino acids; despite not drinking any water, these animals won’t get dehydrated because the can again rely on their fat deposits for sustenance. However, bears do block up their butts in order to keep those initial digestions are bay. To do so, they swallow a mixture of pinecones, bark, and their own hair; this creates a natural digestive cork that they are then able to forcefully pass once permanently awakened.
Many amphibians hibernate in summer
Certain species need to avoid high heat and drought, so they hibernate in the hottest months of the year. This is known as estivation, and is most common for reptiles and amphibians. Estivation is similar to torpor in that these animals are more easily awakened, should any threat arise; their muscles stay limber and their physiological changes aren’t usually as steep.
Snails are basically tiny, parked Volkswagens
In some extremely dry climates, native snails can hibernate for years (though many will estivate all summer). They curl up inside their shells—thanks, mobile home—and their bodies create a film of chalk and slime to cover the exposed hole. As if they aren’t sluggish enough, they can stay dormant like that while burning almost no energy, and requiring no food whatsoever.
Fish hibernate, too
Well, at least one type does. British Scientists discovered that Notothenia coriiceps, a species of Antarctic Cod goes into a sleep-like state during the darkest, dreariest months of the year. Its “hibernation” is not trigged by seasonal changes in temperature, but rather light levels. The question of what they’re saving their energy for is still a head scratcher.
Dormice will doze for 11 nonths straight
After implanting tracking chips inside Australian Dormice, scientists from the University of Veterinary Medicine in Vienna, Switzerland found that some of the tiny creatures remain in hibernation for 11 months at a time. The reason, it seems, is that if it’s not time to mate, it’s safer for them to remain asleep then run the risk of going out into the world while foraging.
But the longest hibernator is the Pygmy Possum
The mini marsupial has been recorded dozing for more than a year — 367 days to be exact. It seems that the creature remains curled up for such lengthy periods of time to prevent getting gobbled up by predators. That, or it just really loves sleep.