Hibernation is a period of slowing down of life processes and metabolism in homeothermic animals during periods of low food availability, when it is impossible to maintain activity and high level metabolism. Characterized by a decrease in body temperature, slowing of breathing and heartbeat, inhibition nervous activity(so-called “deep sleep”) and other physiological processes.
Hibernation can last from several days to several months depending on the species, external temperature and other environmental conditions. During hibernation, there are periods when body temperature is restored to normal values. During hibernation, the animal’s body is nourished by the reserves of nutrients accumulated the day before (fat, etc.).
The animal traditionally considered capable of hibernation is the bear. But the degree to which a bear's metabolic processes slow down in winter is much less than that of rodents, insectivores and other animals, so biologists usually believe that this cannot be called hibernation in the true biological sense. Also, during hibernation, a bear’s body temperature does not decrease very much (from 37° to about 31°C), and is easily and quickly restored; while in ground squirrels (genus Xerus) the body temperature during hibernation can drop to −2°C. A process similar to hibernation is known in several species of reptiles, but it is not yet known whether it is true hibernation.
For several decades it was believed that giant shark in winter, descending to the bottom horizons northern regions ocean, hibernates. But research conducted in 2003 by David Sims refuted this, showing that sharks are actively moving at this time in search of places with the largest number plankton.
Causes of hibernation
Bears are large animals. To feed themselves, they need a lot of food. These predators are omnivores, but some prefer animal food, while others prefer plant food. In the cold season, it becomes difficult to get a second one, and to hold out for a long time Only eating other living creatures is difficult for bears. The lack of opportunity to eat normally leads to the fact that they hibernate.
Polar bears having no problems with food all year round, because their diet consists of seal meat and fish, it is for this reason that they do not need long sleep. Moreover, in winter it is easier to hunt them strong ice. But polar bears also sleep. On the go and more sensitively and briefly, in the spring and winter. Their brown relatives hibernate due to lack of food. Sleep ensures the saving of oxygen in the den, as well as the consumption of useful substances that animals accumulate during the period of activity. It is unknown what prevents them from stocking up on acorns, roots, nuts and other food. Move to warmer climes It’s also difficult for bears: they lead a sedentary lifestyle, making migrations only when necessary to find new places for food. All this together forces us to look for a different way to survive in cold and hungry times.
Preparation
Bears prepare for hibernation thoroughly, starting at 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 fatty acids predominate. Fats will help you survive 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 and the concentration increases carbon dioxide and the temperature drops environment. And each of these reasons also contributes to the animal’s hibernation.
What does a bear eat before hibernation?
Before going into a den, the owner of the taiga needs to accumulate nutrients. The bear is an omnivore, but most his diet in Kuznetsk Alatau, as in many other places, consists of food of plant origin: berries, herbaceous plants, acorns, nuts.
Pine cones are one of the favorite delicacies of bears and one of the best fattening foods. Young animals can climb trees behind them and break off branches. But mostly they collect fallen cones from the ground. To get to the nuts, the bear collects the pine cones in a pile and crushes them with its paws, from where it then, lying on the ground, picks out the nuts along with the shell with its tongue. The shells are partially discarded during the meal and partially eaten.
Often the attention of bears is attracted by the stocks of nuts made by chipmunks. By digging up the animals' burrows, bears get to the nuts and eat them, often together with the owner. They do not miss the opportunity to feast on ant larvae, bird eggs or fish; they also hunt small rodents and ungulates. A brown bear rarely kills wild ungulates itself; it mainly devours them as carrion or takes the prey of other predators (wolves, lynxes, wolverines).
There are known facts of predators eating such species of wild ungulates as elk, deer, and roe deer. He covers the prey or found carrion with brushwood and stays nearby until he eats the carcass completely. If the animal is not very hungry, it often waits several days until the meat becomes softer.
It is very important how productive the year was for fattening feed. Lean years can greatly delay the time for bears to go to dens, and animals can continue to feed even in twenty-degree frosts and almost half a meter of snow cover, digging out cones from under the snow, trying to gain the fat reserves necessary for wintering. In years favorable for food, adult bears accumulate a layer of subcutaneous fat up to 8-12 cm, and the weight of fat reserves reaches 40% total weight beast. It is this fat accumulated over the summer and autumn that the bear’s body feeds on in the winter, surviving the harsh winter period with the least deprivation.
These are animals that have not had time to gain sufficient fat reserves, which is why they cannot hibernate. Connecting rods, as a rule, are doomed to death from hunger and frost or from a hunter. But not every bear encountered in the forest in winter will be a crank. During “after-hours,” bears appear in the forest, whose sleep in their den is disturbed. Normally well-fed, but torn from hibernation the bear is forced to look for a new, quieter place to sleep. Animal sleep is often interrupted by human disturbance.
Bear's den
Before heading to the den, the bear diligently confuses its tracks: it meanders, walks through windbreaks, and even walks backwards along its own tracks. For dens, they usually choose remote and reliable places. They are often located along the edges of impassable swamps, along the banks of forest lakes and rivers, in windfalls and in logging areas. The brown bear makes its winter home in depressions under uprooted roots or tree trunks, sometimes on a pile of brushwood or near an old woodpile. Less often, he chooses a cave for his home or digs deep earthen burrows - ground dens. The main condition is that the home should be dry, quiet and isolated from the presence of unexpected guests. One of the signs of the proximity of a den is large bald spots in the moss, gnawed or broken trees. The animal insulates its shelter with branches and lines the bedding with layers of moss. Sometimes the layer of litter reaches half a meter. It happens that several generations of bears use the same den.
How does a bear sleep in a den?
In the den, in warmth and safety, bears sleep throughout the long and cold winter. Often the bear sleeps on its side, curled up in a ball, sometimes on its back, less often it sits with its head lowered between its paws. If an animal is disturbed while sleeping, it easily awakens. Often the bear itself leaves the den during prolonged thaws, returning to it at the slightest cold snap.
Animals hibernating (for example, hedgehogs, chipmunks, etc.) become numb, their body temperature drops sharply, and, although vital activity continues, its signs are almost invisible. In a bear, the body temperature decreases slightly, by only 3-5 degrees and fluctuates between 29 and 34 degrees. The heart beats rhythmically, although slower than usual, and breathing becomes somewhat less frequent. The animal does not urinate or defecate. Any other animal in this case would have experienced fatal poisoning, and the bears begin a unique process for recycling waste in healthy proteins . A dense plug forms in the rectum, which some call a “plug.” The predator loses it as soon as it leaves the den. The cork consists of tightly compressed dry grass, the fur of the bear itself, ants, pieces of resin and pine needles.
Brown bears sleep alone, and only females who have young yearlings sleep together with their cubs. The duration of hibernation depends on weather conditions, health and age of the animal. But usually this is the period from the second half of November to the first half of April.
Bears fall into stupor, but not into suspended animation
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) and hypothermia (cooling), 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 activity with subsequent restoration under favorable conditions).
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.
Why does a bear suck its paw?
There is a legend among the people that during hibernation the clubfoot sucks its paw. Supposedly this helps him survive the cold winter while he sleeps it off in his lair. But about which paw? we're talking about, no one can really say. Moreover, if you try to find such a picture on the Internet, it is unlikely that you will succeed and this is strange, considering that there is a camera in any mobile phone. So where is the truth?
In fact, everything is much simpler. As scientists have found, the surface of the bear's paws is covered with a very thick layer of skin, which allows it to move on rocky surfaces without feeling any pain. However, after the clubfoot hibernates, under the old layer of skin begins to grow new layer. In order for molting to occur as quickly as possible, the bear moves its paw to its face and begins to bite the old skin. It is also believed that this process can cause some inconvenience to the animal, as the sole begins to itch very much.
There is another, no less interesting version, only it concerns bear cubs that suck their paws if they live in captivity. What is this connected with? The fact is that the baby spends the whole winter with his mother, feeding on her milk. It is worth noting that her nipples are not located along the abdomen, like most animals, but in the groin and armpits. The cub does nothing for several months, feeding on mother's milk and holding the nipple in its mouth. In captivity, it is customary to fatten them from the papilla, like little children. But after eating they are released, and, apparently, they lack contact with their mother, so they begin to suck their paw. This is very rare in nature.
Features of hibernation
- Since it can last up to six months, the bear must have a reserve of the energy it needs. Where can I get it? In fact, it is deposited in subcutaneous fat, which the animal gains during the warm season. In addition, when an animal falls asleep, its body is completely rebuilt. Thus, the rhythm of the heartbeat noticeably decreases, in addition, the bear breathes much less frequently. All this allows him to save both oxygen in the den and reserves of valuable substances in subcutaneous fat, which last for many months. By the way, during this time the animal can lose up to half of its own body weight!
- The clubfoot's sleep is very light; one can say that he sleeps all these long months. Therefore, if a pack of wolves are running near the den and barking loudly, then the bear can easily wake up. And there is nothing good about this, since he turns out to be sleep-deprived and, in search of food, often goes into villages and destroys rural warehouses.
- Bear cubs are also born in dens. There are up to five individuals in one litter, and they weigh only a few hundred grams. They are helpless and blind and suck their mother's milk for the first few months. In the spring, having become a little stronger, they climb out of the den with their mother. They all stay with her for about a year and a half. By the way, you wouldn’t even wish on your enemy to be next to a bear who is on a walk with her babies, because in any danger she is ready to literally tear her opponent to pieces.
Top 5 Animals That Hibernate
Alpine marmot
“Sleeps like a groundhog” - they say about a person sleeping soundly. This is both true and false at the same time. The groundhog is truly one of those animals that prefer to wait out the winter, plunging into sweet dreams. Hibernation lasts about six to seven months, during which the groundhog does not eat or drink, making do exclusively with internal reserves accumulated over the summer. Marmots spend the winter in burrows as a whole family: in the center, where it will be warmest, young individuals go to sleep, and adult animals are located around them. Typically, marmots wake up at the same time every two weeks to get themselves in order, and also fall asleep synchronously again. But if it gets very cold, animals wake up out of schedule in order to use the heat of their bodies to increase the air temperature in the hole.
Gray mouse lemur
Situated in the tropics, Madagascar would hardly be suspected of having such a harsh climate that animals would be forced to hibernate. Still gray mouse lemur so gentle that it resorts to this adaptation mechanism, completely atypical for primates, during the relatively cold and dry Madagascar winter. These animals prefer to get food alone, but relax in the company of their own kind. It is interesting that only females gather in groups to hibernate, but males spend the winter in splendid isolation.
American White-throated Nightjar
The White-throated Nightjar is also called the “sleeper” because it is the only bird that is capable of true hibernation. Nightjars are found throughout the area North America, from British Columbia in the north to central Mexico in the south, where they migrate for the winter. This is what most people do white-throated nightjars, but populations in the states of California and New Mexico prefer to wait out the cold in hibernation, huddled in recesses between stones.
Forest hedgehog
Ordinary forest hedgehogs They hibernate only in places with harsh climates. Moreover, if in females the duration of hibernation depends on air temperature and the availability of food, as in other animals, then males are more sensitive to the level of testosterone in the blood. A decrease in the level of this hormone provokes hibernation, and an increase - a return to an active state. Moreover, in hedgehogs, the level of testosterone is tied to the level of melatonin, which, in turn, depends on the duration daylight hours. However, it is not yet entirely clear how hedgehogs, being deep underground, assess the situation on the surface: daylight hours, ambient temperature and the availability of food. Perhaps this is why they take breaks from hibernation.
American wood frog
In winter, wood frogs that live in Canada and the northern United States look more like skillfully carved figures from variegated jasper, covered with openwork lace made of ice and snow. It's hard to believe that they will come to life once you warm them up. The main threat that cold poses to animals is that fluid in the body turns into ice crystals, which destroy cells. Warm-blooded animals solve the problem by simply maintaining their body temperature above 0 °C, but cold-blooded animals had to turn into real chemical factories for the production of cryoprotectants. Thus, on the eve of winter, the American wood frog not only increases the level of urea in the blood, known for its antifreeze properties, but also accumulates glycogen in the liver. When it gets colder, glycogen begins to turn into glucose. The frog is literally soaked in sugar syrup, which lowers the freezing point (as you know, jam does not freeze). Thanks to these tricks, ice forms only around the cells, and not inside them, which allows wood frogs to successfully tolerate low temperatures.
Video
Sources
- https://www.moya-planeta.ru/travel/view/top10_zhivotnyh_vpadajushhih_v_spyachku_17557/ http://www.nexplorer.ru/print/news__11884.htm https://ru.wikipedia.org/wiki/Hibernation
Every autumn, bears of temperate and polar latitudes (in particular brown and black) begin to prepare for hibernation. All spring, summer and autumn, these animals actively fed, fattening up their fat reserves for the winter. And now, when the cold weather sets in, they are looking for suitable shelter to spend the winter. After the shelter has been found, the bear hibernates.
Hibernation of bears in some cases lasts up to six months. During hibernation, some species, such as the black bear (Ursus americanus), reduce their heart rate from 55 beats per minute to about 9. Their metabolic rate decreases by 53%. Naturally, all this time the bears do not eat, drink or produce waste. How do they do this?
To understand what happens in a bear’s body during hibernation, it is necessary to immediately clarify what hibernation itself is. And why is this not “anabiosis” in the literal sense of the word. In the literal sense of the term, “anabiosis” is the process of complete inactivity of an animal. At this time, the metabolic rate decreases to levels that are incompatible with life for most higher animals.
Some species of amphibians (some newts and frogs) freeze in cold weather, thawing without harm when the warm season begins. This “freezing” is literally painless for them due to the production of a specific substance that has the properties of antifreeze, which prevents the water in their body from freezing.
Bear Den
Bears don't freeze. Their body temperature remains high enough during hibernation, which allows them to wake up in case of any danger, leaving the den. By the way, bears that woke up ahead of time are called “connecting rods.” They pose a significant danger to humans, since in winter the bear cannot find enough food and is always hungry and aggressive.
Some researchers claim that bears do not go into suspended animation, as mentioned above. But there are also scientists who call bears “super hibernators,” since not eating, drinking, or defecating for six months, while remaining able to quickly emerge from hibernation, is unique phenomenon in the animal world.
“In my opinion, bears are the best suspended animals in the world,” says Brian Barnes of the Institute of Arctic Biology at the University of Alaska, Fairbanks.
This scientist spent three years studying the hibernation patterns of black bears.
"Their body is closed system. They can spend the entire winter using only oxygen to breathe, which is all they need,” says Barnes.
Why don't bears defecate during hibernation? In short, it is because a fecal impaction forms in their body at this time. This is a special mass that researchers have long found in the esophagus of hibernating bears.
Previously it was believed that bears eat food before entering their den. a large number of plant material, hair from other bears and other materials that are not digested and which then form a plug in the animal's intestines. The scientists who came to this conclusion relied heavily on information received from bear hunters. They argued that the method of feeding mentioned above led to “fastening of the intestines” and the animal simply could not perform an act of defecation during sleep.
In fact, this is not true. Bears don't eat anything special before hibernation. They, like omnivores, try to consume any food available to them, including fruits, vegetables, nuts, meat, fish, berries and much more.
And during hibernation, the animal’s intestines continue to work. Not in the same activity mode, but it still works. Cells continue to divide and intestinal secretion occurs. All this forms a small amount of feces, which accumulate in the animal’s intestines. A “plug” with a diameter of 3.8 to 6.4 centimeters is formed.
“A fecal impaction is waste material that sits in an animal’s intestines for so long that the intestinal wall absorbs fluids from the mass, leaving it dry and hard,” the North American Bear Research Center says on its website. Thus, the bear’s body does not lose the water it needs, the reserves of which in the den are almost impossible to replenish.
Experts placed cameras in the bears’ dens that recorded everything that happened during hibernation. As it turns out, plant fibers and wool are often integral part traffic jams because a bear, even during hibernation, can pick up something from the ground in its den, and can even lick its fur.
After the bear leaves the den, they clean out the intestines, which begin to function normally. Usually defecation occurs already at the threshold of the den. Therefore, there is no mysticism or mystery, as some hunters or even scientists say, in a bear jam. All this is a product of the body’s vital activity. By the way, the bear in the den does not suck its paw at all. The fact is that in January and February there is a change skin on the pads of the paws. The old skin bursts and itches, which causes the bear certain discomfort. To relieve the itching, the bear licks its paws.
In order to clarify the details of the hibernation process in bears, I requested comments from scientists from Krivoy Rog State Pedagogical University.
How do bears maintain their bodies in a state of hibernation?
Each animal exists due to metabolism and energy, which are provided by the food consumed. Naturally, the more active the lifestyle and the more intense the physiological processes, the more “fuel” in the form of food needs to be introduced into the body. In an organism that is at rest in the form of hibernation, the intensity of all metabolic processes is reduced to a physiological minimum.
That is, exactly as much energy is expended to ensure that the animal remains alive and that degenerative processes do not occur in tissues and organs due to lack of energy. In general, this state can be compared with what happens during normal sleep, but, naturally, it is more “exaggerated”.
The main consumer of energy in the body is the brain and muscles (at least 2/3 of the body’s total energy). But since the muscular system is inactive during sleep, its cells receive exactly as much energy as is necessary to maintain their existence. Therefore, at “low speed” other organs also begin to work, also receiving very little energy.
The digestive system essentially has nothing to digest (since the intestines are almost empty, as mentioned above). Where then does this minimum amount of energy come from, which the beast still needs? It is extracted from fat and glycogen reserves accumulated during the active period of the year. They are used up gradually and usually last until spring.
A gorged bear in autumn
By the way, quite often those bears that “ate poorly” in the summer become connecting rods. There are many oral stories that there are more connecting rods in lean years. So, fat and glycogen reserves are the main source of energy. Another vital substance is oxygen. But since the body is inactive, much less oxygen is needed. Thus, the respiratory rate is significantly reduced.
And if the tissues of the body during hibernation require a very small amount of oxygen and nutrients, then the blood that carries them can move much more slowly. Therefore, the heart rate decreases significantly, and accordingly, the heart also consumes less energy. Saving water is associated not only with “clogging” of the intestines, but with the actual suspension of kidney activity.
Are there other examples of hibernation among warm-blooded animals?
An adaptation such as hibernation in bears is a very unusual phenomenon for warm-blooded animals, but not at all unique. Hedgehogs also have it temperate latitudes, marmots, inhabitants of the Eurasian steppes, and some representatives of the Mustelidae (badger) family.
In particularly cold and hungry winters, squirrels and raccoon dogs can fall into a similar state, but not for long, and their vital processes do not slow down as much as they do in bears. In addition to winter hibernation (hibernation), there is also summer hibernation (estivation). Some inhabitants of hot deserts (some insectivores, rodents, marsupials) fall into the latter.
This happens during the hottest periods of the year, when the extraction of food and water becomes much more energy-intensive and, in fact, ineffective. Therefore, it is easier for the animal to hibernate and wait out unfavorable conditions. In addition to seasonal hibernation, there is also daily hibernation. It is characteristic of some flying warm-blooded animals - hummingbirds and bats.
The fact is that both of them flap their wings very quickly during flight. Thanks to this, their flight has become more maneuverable, and food production has become more efficient. But for everything in nature you have to pay. Their flight muscles consume a lot of energy, which is not enough for a full day (despite the fact that both hummingbirds and the bats During the active phase of the day they consume food weighing more than half of their own weight).
As you can see, their metabolic rate is simply colossal. Therefore, during sleep (and rest in the form of sleep is necessary for every animal - this is also a normal and obligatory physiological process), their vital activity decreases to parameters comparable to those observed in bears.
How does the hibernation state of bears differ from, for example, suspended animation of frogs?
In warm-blooded animals, physiological processes cannot be completely “turned off” during hibernation. That's why they are warm-blooded - they need self-produced heat. A different picture can be observed in poikilothermic animals - their vital processes are almost completely suspended.
That is, the body's cells remain in a practically preserved state until better times come - when the sun warms up and gives enough heat to warm up the body. This happens in all amphibians of temperate and more northern latitudes.
It is a known fact that individuals of the tailed amphibian Siberian salamander, after being literally frozen into ice for several decades (!), after thawing, “came to life” and felt quite normal. Wintering snakes and lizards also go into suspended animation, but their bodies are not so tenacious (they will not survive freezing).
Another example is fish living in drying up water bodies in Africa, South America and Australia, and buried in silt during periods of drought. The processes occurring in their body during this period are close to those that occur in amphibians - an almost complete suspension of vital activity until better times.
As for the reptiles of hot countries, it must be said that, although they are cold-blooded, the experience unfavorable conditions they are more similar to those of warm-blooded animals - a significant decrease in the intensity of physiological processes, but not a stop (there is enough solar thermal energy). Large reptiles(crocodiles, pythons and boas) thus “rest” for up to a year, digesting the large prey they eat.
Is it possible to artificially create a hibernation regime for animals that do not hibernate?
No. It will be an abnormal state like a coma.
How could such a wintering mechanism appear in bears? Was such a mechanism developed over many hundreds of thousands of years or did it appear spontaneously?
All physiological processes are controlled genetically. During the course of evolution certain group individuals, a certain physiological feature could have arisen, consisting in a special sleep pattern (daily, normal) in cold period year, accompanied by a slight decline in physiological activity and a drop in body temperature by 1-2 degrees.
This feature gave these individuals a certain advantage in terms of more economical energy consumption in conditions with less food. At the same time, it began to provide such a great advantage in survival that gradually only such mutants remained in the population.
Subsequently, selection for this trait continued - sleep became longer and deeper, and the intensity of body processes decreased more and more. Finally, the animals learned to make dens.
By the way, this feature could provide a significant advantage also because just during hibernation the female gives birth to cubs and at this time they are warm and protected, hidden from prying eyes. In general, the evolution of the phenomenon of hibernation continued (and maybe continues) for, of course, no less than several hundred thousand years.
Every autumn, bears of temperate and polar latitudes (in particular brown and black) begin to prepare for hibernation. All spring, summer and autumn, these animals actively fed, fattening up their fat reserves for the winter. And now, when the cold weather sets in, they are looking for suitable shelter to spend the winter. After the shelter has been found, the bear hibernates.
Hibernation of bears in some cases lasts up to six months. During hibernation, some species, such as the black bear (Ursus americanus), reduce their heart rate from 55 beats per minute to about 9. Their metabolic rate decreases by 53%. Naturally, all this time the bears do not eat, drink or produce waste. How do they do this?
To understand what happens in a bear’s body during hibernation, it is necessary to immediately clarify what hibernation itself is. And why is this not “anabiosis” in the literal sense of the word. In the literal sense of the term, “anabiosis” is the process of complete inactivity of an animal. At this time, the metabolic rate decreases to levels that are incompatible with life for most higher animals.
Some species of amphibians (some newts and frogs) freeze in cold weather, thawing without harm when the warm season begins. This “freezing” is literally painless for them due to the production of a specific substance that has the properties of antifreeze, which prevents the water in their body from freezing.
Bear Den
Bears don't freeze. Their body temperature remains high enough during hibernation, which allows them to wake up in case of any danger, leaving the den. By the way, bears that woke up ahead of time are called “connecting rods.” They pose a significant danger to humans, since in winter the bear cannot find enough food and is always hungry and aggressive.
Some researchers claim that bears do not go into suspended animation, as mentioned above. But there are also scientists who call bears “super-anabiotics”, since not eating, drinking or defecating for six months, while remaining able to quickly emerge from hibernation, is a unique phenomenon in the animal world.
“In my opinion, bears are the best suspended animals in the world,” says Brian Barnes of the Institute of Arctic Biology at the University of Alaska, Fairbanks.
This scientist spent three years studying the hibernation patterns of black bears.
“Their body is a closed system. They can spend the entire winter using only oxygen to breathe, which is all they need,” says Barnes.
Why don't bears defecate during hibernation? In short, it is because a fecal impaction forms in their body at this time. This is a special mass that researchers have long found in the esophagus of hibernating bears.
It was previously believed that before entering a den, bears ate large amounts of plant material, the hair of other bears and other materials that were not digested and which then formed a plug in the animal's intestines. The scientists who came to this conclusion relied heavily on information received from bear hunters. They argued that the method of feeding mentioned above led to “fastening of the intestines” and the animal simply could not perform an act of defecation during sleep.
In fact, this is not true. Bears don't eat anything special before hibernation. They, like omnivores, try to consume any food available to them, including fruits, vegetables, nuts, meat, fish, berries and much more.
And during hibernation, the animal’s intestines continue to work. Not in the same activity mode, but it still works. Cells continue to divide and intestinal secretion occurs. All this forms a small amount of feces, which accumulate in the animal’s intestines. A “plug” with a diameter of 3.8 to 6.4 centimeters is formed.
“A fecal impaction is waste material that sits in an animal’s intestines for so long that the intestinal wall absorbs fluids from the mass, leaving it dry and hard,” the North American Bear Research Center says on its website. Thus, the bear’s body does not lose the water it needs, the reserves of which in the den are almost impossible to replenish.
Experts placed cameras in the bears’ dens that recorded everything that happened during hibernation. As it turned out, plant fibers and wool are often an integral part of cork because a bear, even during hibernation, can pick up something from the ground in the den, and can even lick its fur.
After the bear leaves the den, they clean out the intestines, which begin to function normally. Usually defecation occurs already at the threshold of the den. Therefore, there is no mysticism or mystery, as some hunters or even scientists say, in a bear jam. All this is a product of the body’s vital activity. By the way, the bear in the den does not suck its paw at all. The fact is that in January and February the skin on the paw pads changes. The old skin bursts and itches, which causes the bear certain discomfort. To relieve the itching, the bear licks its paws.
In order to clarify the details of the hibernation process in bears, I requested comments from scientists from Krivoy Rog State Pedagogical University.
How do bears maintain their bodies in a state of hibernation?
Each animal exists due to metabolism and energy, which are provided by the food consumed. Naturally, the more active the lifestyle and the more intense the physiological processes, the more “fuel” in the form of food needs to be introduced into the body. In an organism that is at rest in the form of hibernation, the intensity of all metabolic processes is reduced to a physiological minimum.
That is, exactly as much energy is expended to ensure that the animal remains alive and that degenerative processes do not occur in tissues and organs due to lack of energy. In general, this state can be compared with what happens during normal sleep, but, naturally, it is more “exaggerated”.
The main consumer of energy in the body is the brain and muscles (at least 2/3 of the body’s total energy). But since the muscular system is inactive during sleep, its cells receive exactly as much energy as is necessary to maintain their existence. Therefore, at “low speed” other organs also begin to work, also receiving very little energy.
The digestive system essentially has nothing to digest (since the intestines are almost empty, as mentioned above). Where then does this minimum amount of energy come from, which the beast still needs? It is extracted from fat and glycogen reserves accumulated during the active period of the year. They are used up gradually and usually last until spring.
A gorged bear in autumn
By the way, quite often those bears that “ate poorly” in the summer become connecting rods. There are many oral stories that there are more connecting rods in lean years. So, fat and glycogen reserves are the main source of energy. Another vital substance is oxygen. But since the body is inactive, much less oxygen is needed. Thus, the respiratory rate is significantly reduced.
And if the tissues of the body during hibernation require a very small amount of oxygen and nutrients, then the blood that carries them can move much more slowly. Therefore, the heart rate decreases significantly, and accordingly, the heart also consumes less energy. Saving water is associated not only with “clogging” of the intestines, but with the actual suspension of kidney activity.
Are there other examples of hibernation among warm-blooded animals?
Dormouses set a record for the longest hibernation period among mammals in natural conditions
The most well-fed rodents belonging to the species of dormouse (Glis Glis), able to sleep for up to 11.4 months in bad years for reproduction. The standard hibernation period for these animals is approximately 7-8 months.
An adaptation such as hibernation in bears is a very unusual phenomenon for warm-blooded animals, but not at all unique. It is also found in hedgehogs of temperate latitudes, marmots inhabiting the Eurasian steppes, and some representatives of the Mustelidae (badger) family.
In particularly cold and hungry winters, squirrels and raccoon dogs can fall into a similar state, but not for long, and their vital processes do not slow down as much as they do in bears. In addition to winter hibernation (hibernation), there is also summer hibernation (estivation). Some inhabitants of hot deserts (some insectivores, rodents, marsupials) fall into the latter.
This happens during the hottest periods of the year, when the extraction of food and water becomes much more energy-intensive and, in fact, ineffective. Therefore, it is easier for the animal to hibernate and wait out unfavorable conditions. In addition to seasonal hibernation, there is also daily hibernation. It is characteristic of some flying warm-blooded animals - hummingbirds and bats.
The fact is that both of them flap their wings very quickly during flight. Thanks to this, their flight has become more maneuverable, and food production has become more efficient. But for everything in nature you have to pay. Their flight muscles consume a lot of energy, which is not enough for a full day (despite the fact that both hummingbirds and bats consume food weighing more than half of their own weight during the active phase of the day).
As you can see, their metabolic rate is simply colossal. Therefore, during sleep (and rest in the form of sleep is necessary for every animal - this is also a normal and obligatory physiological process), their vital activity decreases to parameters comparable to those observed in bears.
How does the hibernation state of bears differ from, for example, suspended animation of frogs?
In warm-blooded animals, physiological processes cannot be completely “turned off” during hibernation. That's why they are warm-blooded - they need self-produced heat. A different picture can be observed in poikilothermic animals - their vital processes are almost completely suspended.
That is, the body's cells remain in a practically preserved state until better times come - when the sun warms up and gives enough heat to warm up the body. This happens in all amphibians of temperate and more northern latitudes.
It is a known fact that individuals of the tailed amphibian Siberian salamander, after being literally frozen into ice for several decades (!), after thawing, “came to life” and felt quite normal. Wintering snakes and lizards also go into suspended animation, but their bodies are not so tenacious (they will not survive freezing).
Another example is fish that live in drying up water bodies in Africa, South America and Australia, and bury themselves in mud during periods of drought. The processes occurring in their body during this period are close to those that occur in amphibians - an almost complete suspension of vital activity until better times.
As for the reptiles of hot countries, it must be said that, although they are cold-blooded, their experience of unfavorable conditions is more similar to that of warm-blooded ones - a significant decrease in the intensity of physiological processes, but not a stop (there is enough solar thermal energy). Large reptiles (crocodiles, pythons and boas) thus “rest” for up to a year, digesting the large prey they eat.
Is it possible to artificially create a hibernation regime for animals that do not hibernate?
No. It will be an abnormal state like a coma.
How could such a wintering mechanism appear in bears? Was such a mechanism developed over many hundreds of thousands of years or did it appear spontaneously?
All physiological processes are controlled genetically. During the course of evolution, a certain group of individuals may have developed a certain physiological feature, consisting in a special sleep pattern (diurnal, normal) during the cold period of the year, accompanied by a slight decline in physiological activity and a drop in body temperature by 1-2 degrees.
This feature gave these individuals a certain advantage in terms of more economical energy consumption in conditions with less food. At the same time, it began to provide such a great advantage in survival that gradually only such mutants remained in the population.
Subsequently, selection for this trait continued - sleep became longer and deeper, and the intensity of body processes decreased more and more. Finally, the animals learned to make dens.
By the way, this feature could provide a significant advantage also because just during hibernation the female gives birth to cubs and at this time they are warm and protected, hidden from prying eyes. In general, the evolution of the phenomenon of hibernation continued (and maybe continues) for, of course, no less than several hundred thousand years.
It’s good for those who have wings - they flew away and that’s it. well and brown bear through the thickets and wild forest can’t get to places where the climate is warmer.
And he finds a rather practical solution. In the summer, the bear eats its food and then goes into hibernation until spring. But not everything is as simple as it might seem at first glance. Imagine what you would be like if you didn’t drink or eat for six months. Let's get acquainted with some amazing processes that occur in the body of a bear during hibernation.
Busy summer
To prepare for the six-month “fast,” the she-bear needs to make energy reserves.” So she doesn't worry about her figure. Its main goal is to accumulate more subcutaneous fat (in some places its thickness reaches eight centimeters). Although she likes sweet berries best, she is not picky about food. She eats everything: roots, small mammals, fish and ants. By autumn, she can gain weight up to 130-160 kilograms, a third of which is fat. (The male can weigh up to 300 kilograms.) Before plunging into the world of dreams, she stops eating and emptys her intestines. For the next six months she does not eat anything, does not urinate or defecate.
Bears choose a place for a den in a cave, an abandoned anthill or a depression under the roots of trees. The main thing is that it is quiet there and no one disturbs your sweet sleep. Bears collect spruce branches, moss, peat and other materials to make a warm and cozy bed. The den is not much larger than the massive body of the bear. When winter comes, snow will cover the den and only an attentive observer will be able to see the hole through which air enters there.
Hibernation
Some small mammals, such as hedgehogs, bats and dormouse, fall into real hibernation, that is, they spend most of the winter in a state similar to death. Their body temperature approaches the ambient temperature. But a bear's body temperature only drops by 5 degrees Celsius, so its sleep is not that deep. “You can’t say that a bear ‘sleeps without its hind legs.’ The bear raises its head and turns from side to side almost every day,” says Raimo Hissa, a professor at the University of Oulu in Finland, who has spent many years studying bear hibernation. Yet the bear rarely comes out. from her den in the middle of winter. During hibernation, the animal’s body works “in economy mode.” The heart rate drops to 10 per minute, and the metabolic process slows down. When the bear sleeps sweetly, fats begin to be burned in her body. Fatty tissues are broken down by enzymes and supply the animal's body with the necessary calories and water. Although the processes that support life in the body slow down, a certain amount of waste is generated as a result of metabolism. How can a mother bear get rid of it and at the same time keep her den clean? Instead of removing waste , the body processes them!
Professor Hissa explains: “Urea from the kidneys and bladder is reabsorbed into the blood and transported circulatory system into the intestines, where it is hydrolyzed by bacteria into ammonia.” Even more surprising is that this ammonia goes back to the liver, where it participates in the formation of new amino acids that form the basis of proteins. Converting waste products into Construction Materials, the bear's body feeds itself during a long period of hibernation!
In the old days, people hunted bears sleeping in dens. Sleepy Toptygin became easy prey. First, hunters on skis found a den, then surrounded it. After this, the bear was woken up and killed. Today, winter bear hunting is considered a cruel activity, and it is banned almost throughout Europe.
Studying bear hibernation
The Department of Zoology at the University of Oulu has been conducting research for several years on the physiological processes by which animals adapt to cold. Brown bears began research in 1988, and in total over the years, observations were carried out on 20 individuals. A special den was created for them in the zoological garden of the university. To measure body temperature, study metabolism, vital activity, as well as changes that occur during hibernation in the blood and hormones, scientists used computers, video cameras, and did laboratory tests. Biologists collaborated with specialists from other universities, even Japanese ones. They hope that the research results will be useful for solving problems related to human psychology.
New life
The bear sleeps all winter, turning over from side to side, but what happens in the life of the bear is an important event. Bears mate in early summer, but the fertilized cells inside the expectant mother's body do not develop until the mother hibernates. The embryos then attach to the wall of the uterus and begin to grow. After just two months (in December or January), the expectant mother's body temperature rises slightly and she gives birth to two or three cubs. After this, her body temperature drops again, although it does not become as low as before childbirth. Papa Bear does not see his children being born. But the sight of newborns would probably disappoint him. It would be difficult for a huge dad to recognize these tiny creatures weighing less than 350 grams as his offspring.
Mother bear feeding cubs nutritious milk, this exhausts her already weakened vitality. The cubs grow quickly, by spring they become fluffy and already weigh about five kilograms. This means that the bear’s small “apartment” is full of excitement.
Spring
March. Cold winter has passed, the snow is melting, the birds are returning from the south. At the end of the month, male bears emerge from their dens. But the mother bears remain in their shelter for several more weeks, perhaps because the babies take a lot of their energy.
After a long hibernation, all that remains of a well-fed bear is skin and bones. The snow melted, and with it her fat melted. With all this, the bear is surprisingly mobile - no bedsores, seizures or osteoporosis. Some time after leaving the den, she cleanses the intestines. Typically, bears begin to eat only two or three weeks after waking up, since the body does not immediately get used to the new conditions. But then they develop a remarkable appetite. But since nature itself has recently awakened from winter sleep, then at first there is not much food in the forest. Bears chew larvae and beetles, eat old carcasses, and sometimes even hunt reindeer.
The care of raising cubs falls on the shoulders of the mother bear, and she protects her cubs like the apple of her eye. An ancient proverb says: “It is better for a man to meet a mother bear without children than a fool with his foolishness” (Proverbs 17:12). In other words, it is better not to date either one or the other. “Mama bear has a lot on her plate. If a male bear approaches, she immediately forces the cubs to climb a tree. The point is that the male can harm them, even if he is their father,” explains Hissa.
The cubs spend another winter in the den with their mother. Well, next year they have to look for their own den, since the bear will have new tiny cubs.
We already know a lot about the complex and unusual phenomenon of bear hibernation, but much still remains a mystery. For example, why does a bear become sleepy in the fall and why does it lose its appetite? Why doesn't he have osteoporosis? Uncovering a bear's secrets is not easy, and that's understandable. Everyone has their own secrets!
Loading...
