How Do Animals Hibernate? – (Types of Hibernation in Animals EXPLAINED)
How Do Animals Hibernate?
Hibernation is actually a type of state of dormancy seen in a lot of animals like Hedhogs, Bears, Snakes, Snails, etc.
Hibernation can last at least for about 5 to 6 months depending on the species type when a lot of the animal’s physical activities, development, and growth are halted temporarily.
That’s why we say that hibernation is a type of state of dormancy in the animal.
In some animals, hibernation can last for a few hours as well. That is called false hibernation.
Animals have so far well-adapted themselves to perform hibernation during times of extreme coldness in the winter season.
Animals generally perform the biological process of hibernation by entering into a state of dormancy or periodic inactiveness of the biological body for a time period.
Animals perform hibernation by lowering down their metabolic activities by up to 98% than the normal rate. This is generally done by lowering down their normal body temperature, by slowing down their breathing and respiration rate, by reducing their heartbeat (by up to 95%), and also by accumulating lots of body fats.
In simple words, by lowering down their metabolic rate and storing fats they survive with the least requirement of energy during hibernation.
Also note that during hibernation periods, animals don’t urinate and defecate. Instead, they do convert their urea and the water byproducts to produce proteins in order to maintain the muscles and organ tissue growth during this long state of dormancy.
Also that the metabolic breakdown of fats not only produces the little energy they do need but also a little bit of water too.
So, it can now be clearly mentioned that animals stop eating, breathing, urinating, excreting, sweating, and even drinking water to use less energy during the days of hibernation.
And so, we can also say that they conserve energy by hibernating during the harsh winter conditions.
You can also read this post here about “How Do Hibernating Animals Survive?” to increase your knowledge about this topic. Here you will also learn notable physiological and behavioural adaptation of some animals in order to hibernate and a lot more.
2 Types of Hibernation in Animals
1. Obligate Hibernation
Obligate Hibernation is that type of hibernation in which organisms enter into a phase of dormancy or inactiveness annually based on seasonal timing cues.
They are thought to respond to the synergetic influence of external and internal cues, such as photoperiod and the animals’ circannual rhythm as well.
Meaning that, every year when the winter season approaches they will surely hibernate for months till the winter season is over.
Unlike Facultative Hibernation that occurs occasionally, Obligate Hibernation occurs every year spontaneously as the winter season approaches. That’s why Obligate Hibernation is also called Spontaneous Hibernation.
Obligate Hibernators will surely hibernate every year, and they have well-adapted themselves over the course of evolution to remain inactive only during the winter season every year.
The hibernation patterns and the length of hibernation period remain consistent in the case of obligate hibernators. Meaning that, they will hibernate for the same time period during the winter season every year.
Examples of Obligate Hibernators: White-tailed prairie dogs, Ground squirrels, Mouse lemurs, European hedgehogs, etc.
2. Facultative Hibernation
Facultative Hibernation is that type of hibernation in which organisms enter into a phase of dormancy or inactiveness only when they are in an extremely cold-stressed condition, or there’s little to no availability of food, or in both of the cases.
Meaning that they will only occasionally hibernate for months or days till the cold-stressed, or food-deprived, or both of the situations get over.
Unlike Obligate Hibernation that occurs annually every year, Facultative Hibernation only occurs occasionally when the organism gets stressed and is no longer able to tolerate the extreme cold temperature or food deprivation conditions.
Facultative Hibernators may or may or hibernate depending on their surroundings. They are only seen to hibernate when the surrounding becomes cold-stressed, or food-deprived, or both.
So for Facultative Hibernators, the length of the hibernation period of an organism varies on weather conditions and food supplies, and not on any seasonal cues.
Meaning that, till the period of cold-stressed or food-deprived condition or in both of the situations, facultative hibernators will not hibernate until and unless they can’t any longer tolerate such extreme conditions.
Examples of Facultative Hibernators: Bears, Black-tailed prairie dogs, Pocket mice, etc.
How do animals perform Obligate Hibernation?
Obligate Hibernators perform Obligate Hibernation as soon as their control center of the brain mainly the hypothalamus part of the brain starts to receive seasonal cues from its surroundings.
They perform hibernation from the start to the end of the winter season almost for the same time period every year within their warm burrows.
This gives them the ability to hibernate every year regardless of ambient temperature and access to food.
Meaning that they have no control over their hibernation process. All happens involuntarily in order to help them survive the harsh winter conditions with ease and less use of energy.
As seen during hibernation, their body temperature drops drastically to near ambient temperature and this lessens their body heat production, and their heart and respiration rates also slow down drastically.
They become 90% to 98% inactive and their whole round metabolic rates drastically decrease to about 98%.
This makes them seem like dead animals during hibernation because of the drastic decrease in their all-around metabolic rate. It’s because they remain only active with the use of their 10% brain energy and metabolism activities.
It is also to be noted that their limited activity during Obligate Hibernation does not involve feeding, mating, gestation, or other important life processes at all.
Even the processes like urination and defecation get completely stopped during hibernation. It’s because they can convert their urea, urine, and other water byproducts to produce proteins in order to support their body tissue growth during such a long period of inactiveness.
Before hibernation, they have already accumulated lots of body fats (at least 50% more body fats than normal) and this helps them survive the winter season without any food and water requirements. And, also they stay active because of their low body metabolism rate.
Usually, it has been seen that they build up body fats during September and October months and hibernate starting in November as the winter starts. Just like in Bats, etc.
So, during the winters you will find these hibernating animals going into a state of hibernation, and some can also be exposed to temperatures below freezing point while remaining hidden within their burrows, and still surviving.
How do animals perform Facultative Hibernation?
Unlike Obligate Hibernators who hibernate every year only during the winter season, Facultative Hibernators may or may not always hibernate every time.
They are seen to only hibernate when they get in a very cold-stressed environmental condition with very high food scarcity.
They don’t have any definite time period of hibernation and will only hibernate for that following time period till the situation gets to normal conditions with tolerable weather conditions and balanced food availability.
They hibernate due to extreme temperature or food deprivation, and also that their hibernation patterns are not as consistent as obligate hibernators’.
They do only go into a light hibernation-like sleep and stay in their burrows for a few days in order to pass the extreme conditions for survival.
Although they don’t hibernate for a very long time period like Obligate Hibernators, and so they are only seen to reduce their body metabolism rate to up to 20% to 30% only.
Their respiration and breathing rates don’t get significantly reduced and so they can wake as per their wish whenever required in order to eat, and perform other essential life activities as well.
But, it has been seen in the majority of the Facultative Hibernators that they completely stop their mating, breeding, and reproductive cycle during hibernation times.
So, maybe that’s why they are often seen to well-prepare themselves just before the extreme conditions arrive. For doing so they start to store their food products beforehand in the burrows to make up most of their dietary needs.
Also that some of the Facultative Hibernators can also be seen foraging in the wild in search for food.
Unlike Obligate Hibernators who lower down their normal temperature during hibernation, Facultative Hibernators remain normo-thermic throughout winter times meaning that they do maintain a condition of normal body temperature.
Facultative Hibernators can be mostly seen to maintain a normal body temperature and physiological rates during their active period of the day.
However, as they get inactive due to extreme intolerable environmental conditions, they ienter into a lighter to deeper sleep that allows them to conserve energy and survive the harsh conditions of the winter.
Notably, there’s one more thing I must mention here that as the Facultative Hibernators arouse from their sleep then it takes for them at least around half an hour to one hour after violent shaking and muscle contractions to become active again.
Such violent shaking and muscle contractions require energy, and this energy requirement is fulfilled with that energy that the animal has saved while hibernating.
What is True Hibernation & False Hibernation?
1. True Hibernation
True Hibernation is that type of hibernation in which the animals enters into an state of dormancy or inactiveness and go for deep sleep during the whole winter months.
During true hibernation, the hibernating animals are known to decrease their body metabolism rate drastically to upto 90% at least. Their breathing, respiration, circulatory rates decreases drastically as well.
True Hibernators will start to gather body fats months before they hibernate. These body fats will help them fulfill their nutritional and energy requirements during their time of hibernation as they will completely stop feeding during this time.
True Hibernators won’t excrete and urinate as well while hibernating. In fact, you will find these animals to be a dead one with no activity at all while being hidden in their burrows or homes.
In a way, it is not at all easy to wake up a true hibernator from deep sleep if the winter season is not over. This is because they are not actually sleeping but as their brain activity is lowered they get inactive.
They will only arouse from their hibernation when they will get seasonal cues from the surrounding indicating that the winter season is over.
And, if somehow, you are able to wake up a hibernating animal in midwinter, you would be effectively killing it. And, so chances are high that it can die very soon.
So, we can finally conclude that during True Hibernation the animal itself enters into a phase of strict dormancy for passing the winter in a resting state of deep sleep. During that time, they show a considerable decrease in their metabolic rate and in body temperature as well.
So, in terms of biology when we use the word hibernation we technically mean it to be true hibernation to refer to general inactivity and dormancy as stated above.
2. False Hibernation
False Hibernation is a type of hibernation in which the animal enters into a state of lower body temperature, or sometimes normal body temperature also, along with lowered breathing rate, lowered heart rate, and also lowered metabolic rate only a bit (maybe up to 10% to 30%) during times of extreme and intolerable environmental conditions.
Under such a type of hibernation, the animals can go for light sleep for shorter period of times, may be for a few hours or rarely a few days.
Sometimes it has been seen that false hibernation can last just through the night or day depending upon the feeding patterns of the animal.
Unlike true hibernators, false hibernators can woke up every now and then in order to eat, urinate, defecate, or perform other necessary life activities and then, they will again go to sleep.
In simple words you can say that, they remain hidden inside their burrows in order to protect them from the extreme weather conditions and food scarcity situations.
In this way they conserve the little energy they would require to stay during the extreme environmental conditions.
So, one notable feature about false hibernators is that these animals can easily maintain a normal body temperature and physiological rates when they are active.
But while they are inactive, they enter into a deep sleep that allows them to conserve energy and survive the winter.
In some of the books of Zoology, you will find that the authors’ term False Hibernation as Torpor which is also a state of dormancy. Some often refer False Hibernation to Facultative Hibernation as well.
Answered: Why do animals hibernate?
So, from the whole context of this article, we can easily make out that animals hibernate in order to pass the extreme environmental conditions so that they can conserve energy and thrive well by following a reduced rate of their bodies’ overall biological processes.
In the case of Obligate Hibernators, they perform true hibernation process and enter into a phase of long time deep sleep during the whole winter season.
And in the case of Facultative Hibernators, they perform false hibernation process and enter into a phase of light or deep sleep during the extreme cold conditions only for a shorter period of time.
So, in both of the hibernation types they try to conserve energy just in order to survive when food is scarce, and all of this happens during the cold winter season only.
As during food scare conditions, hibernation allows animals like bears, etc. to use their stored energy much more slowly and stay alive.
And so, a lot of animals have well-adapted themselves to hibernate by going into a long deep sleep which helps them bypass this period of extreme coldness and food scarcity completely (for obligate hibernators) or partially (for facultative hibernators).
They only wake up when food becomes more plentiful, and external environmental conditions come back to a normal tolerable rate.
