Do polar bears hibernate? Do polar bears hibernate in winter? Which bears hibernate?

Surprisingly, they barely sleep! That is, they sleep normally, just like in the summer (only in the summer they usually sleep more). But they do not fall into winter sleep. (“Hibernation” of bears is more correctly called winter sleep; bears do not have real hibernation, since their body temperature hardly drops, and they can wake up at any moment.) Only females who are pregnant and nursing newborn cubs fall into winter sleep. The rest of the polar bears, if they lie in dens, do so only for a short time and not every year.

And this is surprising because the polar bear is the closest relative of the brown bear. They descended from common ancestors who lived only 150 thousand years ago (this is very recent for the evolution of species). Even in wildlife these species sometimes interbreed. At the same time, in their way of life, polar bears differ sharply from brown bears.

The main food of polar bears is seals. These are such seals. Polar bears hunt them on the ice. They either snatch the seal with their paw from a hole in the ice through which the seal is breathing, or they lie in wait and grab seals that have climbed out onto the ice to rest. In many areas of the Arctic where polar bears live, the ice almost completely melts by the end of summer. They can no longer hunt seals. On land, most Arctic animals are able to escape from polar bear, and into the sea - to swim away from it. It’s good if you can find the carcass of a dead whale or walrus on the shore. And if not, then at the end of summer and autumn the bears sometimes starve for several months. So in winter they do not sleep, but start hunting again as soon as ice appears.

But the females have nowhere to go - they have to lie down in dens. After all, polar bear cubs, like other bears, are born small (their weight is less than a kilogram) and blind; they are covered only with short fluff. Usually females make a den on the shore, sometimes 50 km from the seashore. As a rule, a bear makes a den in a snow dune, but if there is not enough snow, she can dig a hole in frozen ground. The female lies down in a den just when the ice melts and hunting becomes difficult. Cubs are usually born in November-January, and remain in the den until February-March. Before the cubs are born, the mother bear actually sleeps mostly, but during childbirth she wakes up, and after giving birth she has to sleep less. However, before leaving the den, she is still in a state winter sleep: does not eat, does not drink, does not pee or poop.

How does a female manage to accumulate nutrients For long sleep and for feeding cubs (and there are usually two of them)? It turns out that polar bears mate in the spring - in April-May. Immediately after mating, pregnant females begin to feed so intensely that by autumn they become 200 kg heavier - their weight sometimes almost doubles! At the same time, the development of embryos in the bear’s abdomen in the spring stops at early stage and lasts only in autumn; Before this, they are in a state of rest (this is scientifically called embryonic diapause). Apparently, this allows female bears to “adjust” the onset of embryo development to the time they enter the den; after all, this time greatly depends on the conditions in the area and even on the weather in given year.

It’s not very clear why all polar bears shouldn’t eat their fill in the same way. But for some reason they don't do this.

It is interesting that, apparently, at any time of the year, during prolonged fasting, polar bears seem to “sleep on the move.” The concentration of urea in their blood drops sharply, which is typical for other species of bears during hibernation. Bears are able to use urea to synthesize amino acids and proteins in the plasma (liquid part) of the blood. (The concentration of proteins in plasma should be as constant as possible, otherwise various problems with fluid transport and metabolism in the body arise.) In addition, the lower the urea content, the less it needs to be excreted in the urine, which means the less you need to drink. Although water in the form of snow is usually readily available in the Arctic, drinking (or rather, eating) it is energetically unprofitable - a lot of energy is lost to warm it.

If a brown bear's urea concentration has decreased, it becomes lethargic, no longer wants to eat, and falls asleep. But the polar bear, in the presence of food, begins to eat again and raises the concentration of urea to normal level.

It is interesting that during the period of winter sleep, the polar bear somehow manages to lose almost no mass of bones and muscles. Usually in humans and other animals their weight decreases sharply with prolonged immobility, even when there is food; The mass of bones and muscles also decreases in other species of bears during sleep. But the polar bear uses almost only fat. It turns out that in some respects polar bears are better adapted to winter sleep.

Ksenia Kondrasheva answers,

Candidate of Biological Sciences:

They prepare in advance

Bears prepare for hibernation thoroughly, already from the end of summer - when daylight hours begin to shorten, and there is still plenty of food. The process can be compared to fattening a pig: the bear consumes up to 20,000 kcal per day, gaining up to 15 cm of fat per season. In addition to the usual fat - white - there is also brown fat, in which unsaturated fats predominate. fatty acid. Fats will help you survive a long period without food.

Technically, hibernation looks like this:

- tocopherol, which accumulates in adipose tissue and in the liver, inhibits the level of metabolism;

- the level of serotonin increases in the brain, which, having a powerful vasoconstrictor effect, sharply suppresses the activity of the central nervous system, endocrine and other organs, slows down heat formation, which leads to a decrease in body temperature and also a decrease in metabolism;

- in the den where the bear goes before hibernation, the oxygen content decreases, the concentration of carbon dioxide increases and the temperature decreases environment. And each of these reasons also contributes to the animal’s hibernation.

They fall into stupor, but not into suspended animation

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During hibernation, serious changes occur in the bear's body: due to a decrease in body temperature, the concentration of carbon dioxide in the blood increases, and an increase in blood acidity in combination with other factors causes a slowdown in breathing and heart rate. Under the influence of hypoxia (lack of oxygen. - Ed.) and hypothermia (cooling. - Ed.) complete muscle relaxation and slight numbness.

This state of reduced functional activity of living organisms, caused by factors external environment, is called hypobiosis (and this is not the same as suspended animation; suspended animation is the suspension of the body’s vital functions with subsequent restoration under favorable conditions - Ed.).

The breathing and heart rate of a hibernating bear decreases four to five times, body temperature drops by 2-7 °C, and general level metabolism - by 50-70%. Due to fat reserves large bears can exist in a state of sleep for several months. All this time they maintain a constant high temperature bodies and basic physiological processes, retain the activity of most tissues (wounds received before hibernation heal on them and new hair appears where hairline was damaged) and organs, as well as the constancy of the internal environment.

They don't eat or urinate

A hibernating bear uses very little energy to maintain life. Instead of getting it from food, it slowly burns the fat accumulated over the summer. When fat is completely burned, carbon dioxide and water are formed. During hibernation, the bear does not urinate, that is, practically does not lose water. Therefore, even without water, the animal is able to maintain its water balance tolerably by burning fat. Losses in a bear’s body weight over the entire hibernation period range from 15 to 25%.

They are not alone

Just like bears, in winter the badger, raccoon dog and striped raccoon fall into a long sleep. But marmots, gophers, hedgehogs, the bats, some amphibians and reptiles dive into deep hibernation: Their body temperature can drop to sub-zero values, and their heart beats only once or twice a minute.

Many people think that animals hibernate because the weather gets cold where they live. And since the polar bear lives where it is very cold, it must certainly hibernate. But animals hibernate because food supplies become scarce in winter. They do not store supplies for the winter, but instead go to bed. At this time, a reserve of fat is maintained on their body, which they gradually feed on throughout the winter. During hibernation, all life processes almost stop. Body temperature drops, breathing slows, and the heart beats weakly.

Is the same thing happening with polar bears? The answer to this question is negative. In winter, polar bears sleep more than in summer, but this is not the well-known hibernation of animals. The temperature and breathing of polar bears remain normal. They sleep in burrows and caves made of snow and ice. During warmer weather, bears can wander all day and even at night.

Female polar bears sleep more in winter than males. They lie in a den and are covered with snow, sometimes for weeks. During this winter sleep, the young are born. They are very small at birth, weighing between 170 and 230 grams. Therefore, the mother bear takes care of them somewhat winter months. In the spring, hibernating animals wake up from changes in temperature, humidity and hunger. They crawl out of their dens and begin to feed.

Only pregnant females and those nursing newborn cubs fall into winter sleep. The rest of the polar bears, if they lie in dens, do so only for a short time and not every year.

Surprisingly, they barely sleep! That is, they sleep normally, just like in the summer (only in the summer they usually sleep more). But they do not fall into winter sleep. (“Hibernation” of bears is more correctly called winter sleep; bears do not have real hibernation, since their body temperature hardly drops, and they can wake up at any moment.) Only females who are pregnant and nursing newborn cubs fall into winter sleep. The rest of the polar bears, if they lie in dens, do so only for a short time and not every year.

And this is surprising because the polar bear is the closest relative of the brown bear. They descended from common ancestors who lived only 150 thousand years ago (this is very recent for the evolution of species). Even in the wild, these species sometimes interbreed. At the same time, in their way of life, polar bears differ sharply from brown bears.

The main food of polar bears is seals. These are such seals. Polar bears hunt them on the ice. They either snatch the seal with their paw from a hole in the ice through which the seal is breathing, or they lie in wait and grab seals that have climbed out onto the ice to rest. In many areas of the Arctic where polar bears live, the ice almost completely melts by the end of summer. They can no longer hunt seals. On land, most Arctic animals are able to outrun a polar bear, and in the sea, they can swim away from it. It’s good if you can find the carcass of a dead whale or walrus on the shore. And if not, then at the end of summer and autumn the bears sometimes starve for several months. So in winter they do not sleep, but start hunting again as soon as ice appears.

But the females have nowhere to go - they have to lie down in dens. After all, polar bear cubs, like other bears, are born small (their weight is less than a kilogram) and blind; they are covered only with short fluff. Usually females make a den on the shore, sometimes 50 km from the seashore. As a rule, a bear makes a den in a snow dune, but if there is not enough snow, she can dig a hole in frozen ground. The female lies down in a den just when the ice melts and hunting becomes difficult. Cubs are usually born in November-January, and remain in the den until February-March. Before the cubs are born, the mother bear actually sleeps mostly, but during childbirth she wakes up, and after giving birth she has to sleep less. However, before leaving the den, she is still in a state of winter sleep: she does not eat, does not drink, does not pee or poop.

How does the female manage to accumulate nutrients for a long sleep and for feeding her cubs (and there are usually two of them)? It turns out that polar bears mate in the spring - in April-May. Immediately after mating, pregnant females begin to feed so intensely that by autumn they become 200 kg heavier - their weight sometimes almost doubles! At the same time, the development of embryos in the female bear’s abdomen stops at an early stage in the spring and continues only in the fall; Before this, they are in a state of rest (this is scientifically called embryonic diapause). Apparently, this allows female bears to “adjust” the onset of embryo development to the time they enter the den; after all, this time greatly depends on the conditions in a given area and even on the weather in a given year.

It’s not very clear why all polar bears shouldn’t eat their fill in the same way. But for some reason they don't do this.

It is interesting that, apparently, at any time of the year, during prolonged fasting, polar bears seem to “sleep on the move.” The concentration of urea in their blood drops sharply, which is typical for other species of bears during hibernation. Bears are able to use urea to synthesize amino acids and proteins in the plasma (liquid part) of the blood. (The concentration of proteins in plasma should be as constant as possible, otherwise various problems with fluid transport and metabolism in the body arise.) In addition, the lower the urea content, the less it needs to be excreted in the urine, which means the less you need to drink. Although water in the form of snow is usually readily available in the Arctic, drinking (or rather, eating) it is energetically unprofitable - a lot of energy is lost to warm it.

If a brown bear's urea concentration has decreased, it becomes lethargic, no longer wants to eat, and falls asleep. But when food is available, the polar bear begins to eat again and raises the urea concentration to normal levels.

It is interesting that during the period of winter sleep, the polar bear somehow manages to lose almost no mass of bones and muscles. Usually in humans and other animals their weight decreases sharply with prolonged immobility, even when there is food; The mass of bones and muscles also decreases in other species of bears during sleep. But the polar bear uses almost only fat. It turns out that in some respects polar bears are better adapted to winter sleep.

Surprisingly, they barely sleep! That is, they sleep normally, just like in the summer (only in the summer they usually sleep more). But they do not fall into winter sleep. (“Hibernation” of bears is more correctly called winter sleep; bears do not have real hibernation, since their body temperature hardly drops, and they can wake up at any moment.) Only females who are pregnant and nursing newborn cubs fall into winter sleep. The rest of the polar bears, if they lie in dens, do so only for a short time and not every year.

And this is surprising because the polar bear is the closest relative of the brown bear. They descended from common ancestors who lived only 150 thousand years ago (this is very recent for the evolution of species). Even in the wild, these species sometimes interbreed. At the same time, in their way of life, polar bears differ sharply from brown bears.

The main food of polar bears is seals. These are such seals. Polar bears hunt them on the ice. They either snatch the seal with their paw from a hole in the ice through which the seal is breathing, or they lie in wait and grab seals that have climbed out onto the ice to rest. In many areas of the Arctic where polar bears live, the ice almost completely melts by the end of summer. They can no longer hunt seals. On land, most Arctic animals are able to outrun a polar bear, and in the sea, they can swim away from it. It’s good if you can find the carcass of a dead whale or walrus on the shore. And if not, then at the end of summer and autumn the bears sometimes starve for several months. So in winter they do not sleep, but start hunting again as soon as ice appears.

But the females have nowhere to go - they have to lie down in dens. After all, polar bear cubs, like other bears, are born small (their weight is less than a kilogram) and blind; they are covered only with short fluff. Usually females make a den on the shore, sometimes 50 km from the seashore. As a rule, a bear makes a den in a snow dune, but if there is not enough snow, she can dig a hole in frozen ground. The female lies down in a den just when the ice melts and hunting becomes difficult. Cubs are usually born in November-January, and remain in the den until February-March. Before the cubs are born, the mother bear actually sleeps mostly, but during childbirth she wakes up, and after giving birth she has to sleep less. However, before leaving the den, she is still in a state of winter sleep: she does not eat, does not drink, does not pee or poop.

How does the female manage to accumulate nutrients for a long sleep and for feeding her cubs (and there are usually two of them)? It turns out that polar bears mate in the spring, in April-May. Immediately after mating, pregnant females begin to feed so intensively that by autumn they become 200 kg heavier - their weight sometimes almost doubles! At the same time, the development of embryos in the female bear’s abdomen stops at an early stage in the spring and continues only in the fall; Before this, they are in a state of rest (this is scientifically called embryonic diapause). Apparently, this allows female bears to “adjust” the onset of embryo development to the time they enter the den; after all, this time greatly depends on the conditions in a given area and even on the weather in a given year.

It’s not very clear why all polar bears shouldn’t eat their fill in the same way. But for some reason they don't do this.

It is interesting that, apparently, at any time of the year, during prolonged fasting, polar bears seem to “sleep on the move.” The concentration of urea in their blood drops sharply, which is typical for other species of bears during hibernation. Bears are able to use urea to synthesize amino acids and proteins in the plasma (liquid part) of the blood. (The concentration of proteins in plasma should be as constant as possible, otherwise various problems with fluid transport and metabolism in the body arise.) In addition, the lower the urea content, the less it needs to be excreted in the urine, which means the less you need to drink. Although water in the form of snow is usually readily available in the Arctic, drinking (or rather, eating) it is energetically unprofitable - a lot of energy is lost to warm it.

If a brown bear's urea concentration has decreased, it becomes lethargic, no longer wants to eat, and falls asleep. But when food is available, the polar bear begins to eat again and raises the urea concentration to normal levels.

It is interesting that during the period of winter sleep, the polar bear somehow manages to lose almost no mass of bones and muscles. Usually in humans and other animals their weight decreases sharply with prolonged immobility, even when there is food; The mass of bones and muscles also decreases in other species of bears during sleep. But the polar bear uses almost only fat. It turns out that in some respects polar bears are better adapted to winter sleep.