In cold weather, various species of animals fall into a night of long winter sleep. It’s not just bears that hibernate. Today we know them closely.
Many of us imagine hibernation with the image of animals huddled in a dark, quiet, and cozy place and sleeping peacefully for a few months until spring returns. But it is not so. Hibernating animals enter a state of inactivity by slowing down their heart rate and respiration and lowering their body temperature and metabolism.
All of this means that they can survive long periods without eating, but they need to get up from time to time to find food and relieve themselves. Hibernating carries risks, because if an animal cannot store enough fat or cannot find enough food after waking up, it may not survive. And if a hibernating creature wakes up too early, it can burn off its fat stores too quickly and die.
Which animals spend the winter hibernating?
Surely the first that comes to mind is the bear. And it is that, in common ideology, most people immediately think of bears. So, for example, black and brown bears are just two of seven mammals that huddle in burrows or sleep during Alaska’s cold, dark season, but bears are not the only animals that hibernate in winter.
Perhaps the most amazing species that falls into a deep sleep when temperatures drop too low is the Arctic ground squirrel. For hibernation, Arctic ground squirrels burrow up to three feet above the ground with an insulating layer of snow on top. These squirrels survive in a catatonic state by reducing their metabolism and core body temperature to approximately -2.7 ° C, the lowest known body temperature for a hibernating mammal.
Arctic ground squirrels can hibernate for up to eight months, but increase their metabolic rates and body temperature for periods of 12 to 14 hours every 20 days or so. Why this pause? Scientists do not know why they wake up periodically but suspect that they may need to warm up to replenish or remove substances that have been depleted or accumulated during hibernation.
When the weather is cold and food is scarce, animals become inactive to save energy. This is the main reason for going into this deep state of inactivity. During hibernation, the heart rate and respiration slow down and the body temperature drops, as we have seen.
Animals hibernate in many different ways, from snails, which cling to a surface, cover themselves with their slime and thus wait all winter, to hedgehogs, who like to build nests out of grass, leaves, and straw, often underground.
For example, unlike bats, bears are unusual hibernators due to their large size. They also stand out because they do not precisely fall into a “lethargy” or a decrease in consciousness, like most animals that do hibernate. Bears are aware of their surroundings and can even get up and attack when disturbed in winter.
10 animals that hibernate in the winter
Let’s take a closer look at the top 10 animals that hibernate in the winter:
Bears move their dens for hibernation depending on climate changes. They usually hibernate for six to seven months and during this stage, they do not decrease their body temperature as much as other species that also hibernate (they usually lower their body temperature by about 10 degrees).
They do reduce their respiratory rate from 6 to 10 breaths per minute to one breath every 45 seconds, and their heart rate drops from 40 to 50 to just 8 to 19 beats per minute.
While hibernating, bears live off the fat they accumulate during the warmer months and do not eat, drink or excrete anything in these months.
For females, the level of fat is especially important because they will give birth during hibernation and will spend months nursing their cubs without eating anything. Having eaten nothing for months, they are at greater risk of coming into conflict with humans with certain food sources.
The arctic ground squirrel goes through a curious hibernation process. They are buried one meter from the ground with an insulating layer of snow that covers them and survive by reducing their metabolism and body temperature to the lowest known body temperature for a mammal in hibernation: -2.7 ºC.
In this supercooling state, they conserve energy by lowering their body temperature, as if we were lowering the thermostat at home. However, your body fluids do not freeze even though they lower your body temperature below freezing.
These squirrels can hibernate for up to eight months. All other squirrels, like red squirrels, do not hibernate because they cannot accumulate enough body fat. During the summer, they keep food in different places, and in winter, they sleep up to 20 hours a day, going out only to eat.
The flat-tailed dwarf lemur is the only primate to go through a combined state of hibernation and torpor for an extended period. Endemic to Madagascar, this lemur hibernates during the dry season when water is scarce. It is nocturnal, and during the hibernation period, it also lowers its temperature and increases the heart rate.
Do snails hibernate? That’s right, although not all of them hibernate. They adhere to a surface, cover themselves with their slime, and under this slimy mantle that is sealed with a dry layer of mucus called the epiphragm, they wait for the winter to end. They only do it when the weather is extreme. Depending on the species, snails can hibernate for several months.
Hedgehogs love to build nests out of grass, leaves, and straw, often underground. And, of course, to prepare for hibernation, hedgehogs eat as much as they can during the fall to build up good fat reserves for the winter. They eat all the beetles, caterpillars, and earthworms they can find.
Then, they look for a quiet place to rest for the next several months, making use of whatever materials and hiding places they can locate. If found in urban areas, they can be installed on logs, compost heaps, or under garden sheds.
Creatures like the African hedgehog go into estivation, which represents a shorter period than hibernation.
Regular bees don’t hibernate, but bumblebees do. Queen bees will gorge on pollen and nectar to store fat before digging deep into the ground in early fall to prepare for winter. They can stay there for up to nine months.
Regarding butterflies, most species overwinter in the larval stage, but some hibernate as adults, such as the peacock butterfly. They are installed in outdoor structures such as sheds and farm buildings and go into a dormant state when the weather turns cold.
In Alaska, for example, not much is known about how insects survive the cold winters in this area, but a series of recent studies indicated that at least some insects are extremely adept at surviving freezing temperatures. Some figure out how to freeze without dying or use strategies to avoid freezing even in extreme cold.
Reptiles, such as snakes, lizards and turtles, in cold weather, seek an unused hole and settle to expect lower temperatures because they are cold-blooded since their body temperature is controlled by the environment.
This type of hibernation is called brumation. And the duration of this brumation will depend on the location of its habitat, going from months to a few weeks. During this time, snakes experience waking periods when they go out of their resting place to hydrate.
Most species of marmots that live in Alaska, for example, tend to hibernate in family groups in rock piles or rock fields. They insulate rocky burrows with snow and dry foliage and wait for the good weather to return. Groundhogs are the stars of hibernation.
Their hibernation period can last up to five months, during which time they will lose a quarter of their body weight. During this state, heart rate drops from 80 to 100 beats per minute to just 5 to 10, body temperature drops from 99° to 37° C and breathing drastically slows from 16 breaths per minute to just 2.
In addition to the lack of food and shelter during winter, small mammals such as rabbits, shrews, and mice have to deal with more accelerated heat loss due to their higher surface-to-volume ratio and short, thin fur. So instead of hibernating, some of our forest residents, like those mentioned, go into torpor, which is a much shorter but dormant state.
Some bats also hibernate, particularly those in the northernmost areas where insects are rare in winter. They hibernate in caves, tree cavities, wells, old mines, or even attics. Like bears, bats store body fat before slowing down to save energy and while hibernating, they can survive on just a few grams of stored fat for five to six months.
But unlike bears, bats go into true deep sleep hibernation with a heart rate as low as ten beats per minute. (they normally have about 300-400 beats per minute). Their body temperature is a few degrees above air temperature. It is as if they completely ‘turn off’ when winter comes.
Not only wild animals but also pets like hedgehogs and turtles can enter hibernation in the winter or when it’s too cold. It’s a natural state that helps them survive through harsh conditions by keeping a low metabolic rate.
Do you know other animals that hibernate in the winter? How about some interesting facts about animal hibernation that you would like to share with the rest of the world? Feel free to leave us a comment in the section below.