Why do some animals hibernate and others don't?

Hibernation refers to warm-blooded animals-some mammals and a small number of birds, which will enter a lethargic physiological state by lowering their body temperature in cold seasons. People study animal hibernation, mainly for warm-blooded animals. Because they can control their body temperature accurately and purposefully.

European hedgehog Some mammals (such as bats) hibernate continuously. Hibernation of others (such as Dormouse, Dormouse, Hedgehog, Groundhog or Zoroach) is accompanied by a short awakening.

Winter behavior of hibernating animals

In autumn, hibernating animals have the opportunity to find hibernating places: hollow trunks and caves, which are covered with grass, straw, leaves and hair as cushions. In such a well-arranged shelter, they will curl up in groups of three or five, drooping their eyelids and spend the winter in this low-energy form-torpor (Latin: boring). Their body temperature will drop to 1 to 9 degrees Celsius. All physical functions will be greatly reduced. Breathing is very weak, the heartbeat is slow, and the sensitivity to external stimuli is reduced. If you photograph a hibernating bat with an infrared camera, you will see that the bat's body is dark blue. For example, when a groundhog hibernates, its body temperature will drop from 39 degrees Celsius to 7 degrees Celsius. Heart rate dropped from 100 to 2 or 3 beats per minute. The breathing frequency can be extended to once every hour. Metabolites of the intestine and liver will be collected in the lower part of the intestine and excreted after waking up. Animals stop eating when they hibernate, or eat when they are awake for a short time. Hibernating animals live on their own fat. Especially brown adipose tissue, which is located in the shoulders and neck, is a very important energy source, especially when the outside temperature rises and animals wake up from hibernation, which lasts for several hours. In the second half of the awakening process, animals can raise their body temperature to a normal level by shaking their bodies (flexors and extensors contract at the same time, a high-energy action). The higher the temperature, the faster the animals breathe.

The length of hibernation

The duration of hibernation varies from animal to animal. European hedgehogs are 3 to 4 months old. Hibernating mice can sleep for six to seven months (worthy of the name). But we can't simply think that hibernation is a continuous process for several months. On the contrary, the more common hibernation is intermittent, with a long rest state and a short awakening state inserted in low metabolism. However, animals can't always wake up, because they need to consume energy every time they wake up. Too many times of waking up will lead to premature exhaustion of fat storage, so that when they really wake up next spring, there will be no "fat" available.

Social hibernation

Some hibernating animals such as groundhogs even hibernate in groups. In every hibernating place, as many as 20 adult mice and young mice will be close together, so that they can keep warm with each other and will not be hurt by the sharp drop in temperature. Especially the young rats with less fat storage, they can spend the winter in this hibernation mode.

Possible inducing factors of hibernation

It has always been thought that the inducing factors of hibernation are some external factors, such as the drop of environmental temperature and the lack of food in autumn. However, some experts believe that the gradual shortening of the day is a hibernation signal, which will lead to changes in some internal factors, such as changes in hormone levels and the adjustment of seasonal biological clocks. The biological clock seems to affect animal behavior, such as fat storage and preparation for hibernation. There is also the anesthetic effect of high concentration of carbon dioxide in hibernating places, which may also be the inducing factor of hibernation.

The awakening of spring

The reason for awakening in spring is still unclear. The increase of ambient temperature and the accumulation of metabolites may be awakening signals. When hibernating animals wake up, their body temperature will rise slowly. Hormones can cause brown adipose tissue to decompose, providing energy for the initial increase of body temperature. When the body temperature reaches 15 degrees Celsius, the muscles will start to tremble, further warming the body. In the chest and head with important organs, the temperature will recover faster than other parts of the body.

Negative Effects of Hibernation on Memory

The University of Vienna found in the study of European Citellus dauricus that hibernating for several months will have a negative impact on the memory of hibernating animals. Compared with animals that don't hibernate, European ground squirrels can't solve the tasks they learned before hibernation, such as finding the right route in the maze or controlling the lever of food machines. One possible explanation is that hibernation reduces nerve activity. Scientists have even proved that neuronal connections in the brain will be disconnected during hibernation.

Hibernating bird

Not only mammals hibernate, but also some birds hibernate. Hummingbirds will reduce their metabolism and enter a rigid sleep state when food is scarce and cold. In a state of hunger, the young Louyan will go into a state of temperature change during sleep, so it doesn't need to lower its body temperature as much as a real hibernating animal does. Birds do not hibernate like mammals.

Concept discrimination

winter vacation

The winter rest of brown bears in their nests (German: Winterruhe) is different from hibernation. During the winter break, the body temperature of brown bears will not drop as much as that of real hibernating animals. This winter break without large-scale cooling can also be seen in badgers, squirrels and raccoons. During this winter break, these animals often wake up and change their sleeping posture. Brown bears will spend seven months in their nests, half asleep and half awake, eating, drinking and defecating, and living on their own fat. American scientists have found that this semi-sleep state is caused by a hormone called Hibernation-induced HIT. These substances can make brown bears survive the winter without losing muscle strength. A person in a similar state, such as in a hospital bed, will lose 90% muscle strength.

Winter rest state of deer

Recently, it has been found that the deer will also drop their body temperature to 15 degrees Celsius in winter and enter a dormant state. By reducing the metabolic rate to the night level, deer can survive this cold season. Veterinary research at the University of Vienna found that the richness of food will affect this regulation mechanism of body temperature and metabolism. Protein's abundant food, which is not common in winter, may unnecessarily increase the metabolic rate of animals. Therefore, improper feeding in winter will lead to spring famine, because the metabolism of deer has not decreased in winter, and the consumption of forage in the forest is too large, resulting in a shortage of forage in spring.

Veterinary researchers at the University of Vienna believe that the line between hibernation and winter break is no longer clear. Many animals can lower their metabolism and body temperature through similar regulation mechanisms, and seals and whales may also use the same mechanism during long-term snorkeling.

Frozen state of temperature-changing animals

Contrary to hibernation, it is a frozen state, which can be seen in many warm-blooded animals living in certain climatic regions-snails, some insects, most reptiles (snakes, turtles, lizards) and amphibians (toads, frogs). Newts will last for 3 to 4 months, slow-limbed lizards and dragon vipers will last for 4 to 5 months, and rain frogs and sand lizards will stay frozen for 5 to 6 months.

Summer sleep and dry sleep

There is also summer sleep. Crocodiles and snakes (such as the dead viper) living in tropical areas spend their summers in swamps and other places during the dry season. Burgundy snails living in temperate zones sleep in summer or dry when there is no water. There are also some frogs and toads, such as horned toad or African bullfrog (Pyxicephalus adspersus), who also sleep in summer. The physiological function of summer sleep is to save energy in hot and grain-deficient seasons; Like hibernation, these animals reduce their metabolism when they sleep in summer. The amphibians mentioned above will even reduce the intestinal capacity by 40%. This can reduce the food intake by 60%. When there is no shortage of food, the intestine will return to its original size.