Polar Bears occupy a majority portion of the Arctic Circle and its adjacent land masses that include the covering parts of eight countries: Canada, Greenland, Iceland, Norway, Sweden, Finland, Russia, and the US.
In general, many populations of polar bears are spread in various ranges all the way across the Arctic Circle, seen widely in the regions nearby the sea ice of the Arctic Ocean.
It is important to note that the brown and black bears are not true hibernators during the winter months, but they do hibernate.
While the polar bears do not hibernate at all, in fact, they undergo a different process.
Meaning that the male polar bears and non-pregnant polar bears don’t hibernate and can be seen roaming outside with ease during the winters. In fact, these are only the pregnant female polar bears that enter inside their den (a process called denning, not hibernation) in order to give birth to their cubs and stay with them during the harsh winters.
If polar bears don’t hibernate, then why? If they don’t hibernate, then what do they really do?
Just keep reading, and we will learn more about the related concepts regarding the polar bears to clarify them all.
Do Polar Bears hibernate? If No, then Why?
Polar Bears do not hibernate. In fact, these are only the female pregnant polar bears that follow a process called denning which is similar to hibernation but isn’t hibernation.
No male and female non-pregnant polar bears perform hibernation or denning or any such similar processes.
They can only be seen being in a little torpor state while being freely active and roaming by involving a bit physiological changes in their body, related especially to body temperature, metabolism, and water and fat balance.
The purpose of torpor is to slow down the body’s metabolism rate in order to conserve energy in times of insufficient resources and extreme weather conditions.
When torpor is performed in a long-term mode by any biological system then that state is termed hibernation or inactiveness in which the body metabolism is depressed to less than 5% of normal.
And when torpor is performed in a short-term mode by any biological system then that state is not termed as true hibernation or true inactiveness.
So, polar bears do not hibernate. In fact, they enter into a little bit of torpor mode while staying active in order to tackle the extreme winter conditions.
They do so in a variety of means and the various biological studies have suggested that their system of torpor is evolutionarily advanced.
How do Polar Bears survive in the winter?
Yes, it’s true that Polar Bears do not hibernate, but they do enter into a state of a little bit of torpor during the winters in which they do decrease their body activity a bit by decreasing their body metabolism and internal body temperature a bit.
During torpor state, polar bears remain active and free-roaming in search of food and other resources. Meaning that they do not enter into a state of complete hibernation or inactiveness.
They perform torpor by decreasing their body heartbeat rate, respiration rate, and body temperature slightly.
They do also start to deposit a lot of body fats in their adipose tissues prior to extreme winters, and so they do not eat or release bodily waste much during the winters.
Polar bears plan out their fat reserves before they go to sleep for the cold winter months. This helps them to save energy and survive on less amount of food during the coldest weeks of winter when the food is especially scarce.
They do also protect themselves using the two-layer of fur in their body: the first layer consisting of long oily hairs, and the second layer consisting of thick-wooly hairs.
Their two-layer fur works great in terms of attracting and retaining heat. This helps them pass through the harsh winters of the Arctic.
They have a long body with long necks, and their fat deposits increase during the winter season of the year. Their thick layers of fat and two insulated layers of fur help them in insulation against the cold.
Why & How do the pregnant polar bears den?
Pregnant polar bears den (following the process of denning) during the extreme winters for escaping from the harsh winter conditions and low food abundance just in order to give birth to their cubs protectively and comfortably thus increasing the higher chances of cubs survival.
It is during the spring season when they mate, and after mating the female prepares herself for her possible pregnancy by accumulating enough fat reserves in her body thus gaining as much weight as possible by feeding well prior to winter i.e through the summer and fall.
It is very interesting to note here that after mating the fertile eggs don’t implant until the winter season approaches, and it is only if the female has enough fat to sustain herself and her cubs during the long denning period then only implantation takes place in her reproductive system.
This phenomenon causes her to become successfully pregnant sooner in the winter or later in the fall, and this process is called delayed implantation, only occurring if she has enough fat reserves in her body prior to denning.
So later in the fall and sooner in the winter, she starts to prepare dens thus in order to give birth to her cubs.
She does so by digging a small snow cave in a snowdrift which will be large enough for her and her two to three cubs to stay and roam inside.
In many areas in the Arctic, you will also find that the typical conformation of a den consists of an entrance, a tunnel, and the chamber where the bear builds the nest.
In general, you will always find pregnant females preparing their nests by denning directly making a cave in the snowdrift.
The entrance of the den remains open which gets completely hidden later due to snowfall. Thus, the den completely gets hidden under the snow.
Females probably give birth during the winters in the month of December, and they will stay there with their cubs till the Spring while being sincerely devoted to nursing and caring for their cubs.
During the time when she is denning, she won’t eat or drink, and will fully survive using the fat reserves accumulated in her body prior to the winters.