How Do Hibernating Animals Survive? Here Are Your Answers!

What actually is hibernation? And, How do animals prepare for hibernation?

Hibernation is a physiological and behavioural adaptation of some animals to stay dormant and inactive during periods of harsh conditions in the winters.

The harsh conditions for the hibernating animals can be due to their exposure to extreme cold temperatures, extreme high or low pressures, air deprivation, radiation, dehydration, and starvation due to lack of food availability and cold winters.

The hibernating animals know how and so have evolved themselves to better remain inactive and dormant during such harsh conditions.

And for doing so, they do reduce their body metabolic rates for entering the phase of inactivity till the time their environment becomes normal after a few months.

So, during hibernation, they appear like they have fallen asleep for a few months.

And also, during hibernation the animal’s body temperature, heart rate, and breathing rate, and other metabolic activities, all can drop to significantly lower levels.

Thus, they do need less amount of energy to stay alive during this time period by hibernating as the weather is cold and food is scarce.

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. For example: Frogs, toads, etc.

During such times many of the hibernating animals seems to be almost dead as their heart rates completely stop and also they do stop breathing, but still they are alive and awake as soon as the hibernation period is over.

Just for instance, in frogs, once the weather gets warm and things start to get normal, the frog will also get normal. Its heart and lungs miraculously start working again, and the frog comes back to life.

Yes, and this is what and how hibernation really is. That’s strange but interesting, right?

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How do Hibernating animals survive the long winters without eating?

During hibernation, animals don’t need food because they will reduce their body metabolism drastically.

Metabolism produces heat and endothermic animals use the metabolic heat to keep a stable body temperature.

It is to be noted that during hibernation, their body temperature drops from 35°C to 2°C, and their metabolic rate is reduced by about 98%.

And hibernation is the state of 99% inactivity of the animal’s body that functions to conserve energy when sufficient food is unavailable during the harsh winter conditions.

So, before going to the winter hibernating periods, the animals need to store enough energy as body fats during the normal times of the year.

For doing so, it feeds on food during the normal times of the year, mostly to store enough energy to last through the entire duration of their dormant period of harsh winters.

They eat a large amount of food, and so store the energy in the form of fat deposits in their body. Body fats are actually the future reservoir of energy and they help to maintain the body functions.

And, as they enter their period of hibernation they become dormant and reduce their body metabolism a lot.

And so, soon they will start to utilize the body fats to stay alive during the whole harsh winters without eating and staying inactive.

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How do Hibernating animals survive without water?

During their hibernating periods, animals metabolize their fat reserves to obtain water for the body’s needs.

In simple words, they obtain their water by metabolizing fat reserves, which does produce waste like urine and excreta.

During the normal times, research shows that 84% of fat loss in an animal is exhaled as carbon dioxide, and the remaining 16% of fat is excreted in the form water.

So, in normal times during the conversion of energy, carbon dioxide, and water are byproducts of waste. These wastes are excreted via urine, sweating, exhalation, and excreta.

However, during hibernation periods, instead of urinating and defecating, they convert their urea and the water byproducts to produce proteins in order to maintain the muscles and organ tissue growth during the long sleep.

In easily understandable words, the enough fat that they have gained in their body to burn throughout the winter while maintaining a slower metabolism will not only help them in fulfilling the water requirements but also to gain weight as well.

So, the metabolic breakdown of fats not only produces the little energy they do need but also a little bit of water too.

And, so when you put that little energy and water supply for the need of slow body metabolism, body temperature, and breathing, then they do together end up needing less water than normal.

And as a result they are able to survive during the hibernating conditions without much water.

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So, What actually animals do when hibernating?

Hibernating animals are known to drastically reduce their body metabolism rates by lowering the breathing and respiration rates and body temperatures up to 98% lower than the normal situations.

In general and normal situations during hibernation, the heart rate can drop up to 2.5% of its usual level. And, breathing rate can drop up to 50% to 100% (complete pause on breathing) of its usual level.

During hibernation, they enter into their state of suspended living by becoming dormant and inactive.

Due to becoming dormant and inactive, their breathing and heart rates slow down a lot, and this allows their body temperature to drop drastically, in some cases even below the freezing point.

So, why the temperature of the body drops? We know that metabolism is inefficient and produces heat. And so, as the body metabolism drops, the temperature of the body also drops.

Metabolism is the sum total of all of the catabolic (break down) reactions like glycolysis, the citric acid cycle, the breakdown of muscle protein, etc. and anabolic (synthesis) reactions in the body like the cell growth, mineralization of bone, etc.

The metabolism actually is the rate that measures the amount of energy used to maintain life. And, all of these decreases during the hibernation period a lot and so less energy is required to just keep the body alive but not active.

Animals can also stop eating, breathing, urinating, excreting, sweating, and even drinking water to use less energy during the days of hibernation.

During hibernation, the animals will start to utilize the body fats that they have accumulated by feeding before the hibernation period has started. This fat reservoir in their body provides them the warmth, water, energy, and other nurturing requirements during hibernation.

They subsequently lose 15–27% of their pre-hibernation weight by using their stored fats during their whole period of hibernation. But, they can also gain muscle weight a bit by converting the urea into proteins for muscle building.

It has been also seen that when mammals being warm-blooded animals enters into hibernation, they start acting somewhat like a cold-blooded animal, and so their body temperature starts to vary depending on the temperature around them.

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So, Are animals asleep when they hibernate?

When an animal is hibernating, then it may seem like it is asleep but is actually not if you see it scientifically.

The reason that it is not at all asleep but inactive is that the animal enters into a state of unconsciousness. As consciousness is greatly diminished together with the lowering of body metabolism during hibernation.

Being asleep is a way lot different from hibernating. Hibernating is a long-term state of the body’s inactivity.

However, sleeping is actually a short-term state of taking rest but the body remains active.

During hibernation, the metabolic rate of the body gets lowered down to as low as 98%. However, during asleep the metabolic rates only gets reduced a bit to relax the body.

So, in simple words, the body’s physiological aspects of sleep are similar to hibernation, such as a reduced heart and breathing rate, and lowered body temperature. But these changes during sleep are very slight compared to that of during hibernation.

The brain and the central nervous system are adapted to survive and continue its functioning in a profound state of natural depression by lowering the mammalian brain activity levels. That’s why during hibernation the body gets inactive and unconscious.

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What happens if you wake up a hibernating animal?

Fist of all, as the hibernating animals enter into a phase of unconsciousness so it’s almost impossible to wake them up in the manner you would wake up a sleeping animal.

In fact, they are not actually sleeping but as their brain activity is lowered they get inactive.

You can think of this as an animal that was 100% mentally active but now is 98% mentally active. So, this will cause them to seem like asleep or dead animals.

In fact, the brain waves of hibernating animals closely resemble their wakeful brain wave patterns, though the waves are somewhat suppressed and lowered, so they enter into the activity phase looking like being asleep.

So, it is not so easy to wake it up, as you would need to increase its brain activity a lot.

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.

After being awaken it won’t have that much energy to walk and so it will soon sleep, and the signs will look as if the animals are undergoing sleep deprivation.

The waken up animals need to sleep a lot over the next few days to recover and to again re-enter its hibernation stage.

However, it has also been seen that there’s a huge possibility that it will utilize a lot of its energy to wake itself up. And so, even if it tries to re-enter hibernation it will likely survive because of no energy left in its body for keeping itself alive during hibernation.

There are also animals that show lighter hibernation as they are unable to store enough body fat for their whole hibernating period. So, they wake up periodically for feeding and again re-enters into hibernation.

For example, Hibernating bears are seen to wake up very often during their hibernation months, and so they on occasion can leave their dens.

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How long does hibernation last?

The period of hibernation depends from species to species. Some species can show hibernation for months, some for weeks, and some for a few days.

Hibernation can also depend on various other factors like the surrounding temperature, the time of the year, the individual animal’s body condition, and also on their harsh conditions tolerance level.

Animals that can hibernate for months i.e. anywhere between 100 to 150 days without any wake up in between are better to be considered as true hibernators.

For example: Some animals like groundhogs can hibernate for as long as 150 days or so.

Animals that can go into periods of partial hibernation by getting false response from their environment when kept in captivity are better called false hibernators as they induce a false hibernation attempt.

For example: Hedgehogs in captivity show false hibernation.

False hibernations are not true hibernations and so can continue only for a few days or so.

Some are lighted hibernators like bears that are known to wake up very often after every 15 to 30 days or so, and they again re-enter hibernation.

This wake-up and re-hibernation continue during their whole hibernation period of about 4 to 7 months periodically.

So, true hibernating animals get so inactive that waking for them is difficult and it takes a lot of time and energy.

While light hibernators wake up more often throughout the entire winter and carry on as usual while they are awakened.

In the majority of the cases, you will find that most of the animals hibernate for the entire winter season months. Those are the true hibernators.

Here’s the list of some well-known hibernating animals with their hibernation time periods:

No.	Animal	Hibernation Period
1.	Bats	6 months
2.	Bears	5 to 7 months
3.	Box turtles	3 to 4 months
4.	Ground squirrel	7 to 9 months
5.	Groundhogs	3 to 6 months
6.	Chipmunks	4 months
7.	Bumblebees	6 to 7 months
8.	Hummingbird	3 to 4 months or variable
9.	Prairie Dogs	6 months
10.	Ladybug	3 to 4 months
11.	Skunks	4 months
12.	Common poorwills	1 to 3 months
13.	Hedgehogs	6 weeks to 6 months
14.	Land snails	Up to 3 Years
15.	Marmot	5 to 6 months
16.	Fat-tailed dwarf lemurs	7 months
17.	Lizard	5 months
18.	Geckos	3 to 4 months
19.	Garter Snakes	5 to 6 months
20.	Wood frogs	3 months