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Winters can be hard on animals with cold temperatures, limited food, difficult access to water, and many other things adding to the challenge. One way that some mammals deal with the winter is by avoiding it entirely through the process of hibernation.
Hibernation means much more than just sleeping a lot. Animals that go through true hibernation have their body temperature drop significantly, reduce their heart rate dramatically, and go into a deep sleep for extended periods of time.
Most people think that bears hibernate, and that isn’t exactly true. Or at least not in the same was as it is for chipmunks, hamsters, and other little mammals. Instead, bears such as the Brown bear and Black bear go through something that is called torpor, which is often described as a light hibernation. Their metabolism slows down, but their body temperature only drops a small amount. They don’t get up to hunt, drink, or use the bathroom nearly as often as normal, but it isn’t non-existent either.
One might think that the polar bear would be an ideal candidate for hibernation because it has to endure such long and harsh winters, but that is not the case. In fact, polar bears typically don’t even go through torpor like other bear species.
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Sure, sometimes they are more active than others, but their cycle is unique. Dr. John Whiteman is the Chief Research Scientist at Polar Bears International. He explained it to IFLScience, saying:
“It is important to recognize that winter hibernation represents a suite of physiological and behavioral changes, many of which can be defined on a spectrum rather than a yes/no categorization. Polar bears seem to be a bit better at coping with extended food deprivation – weeks at a time, even during the productive spring hunting season – than other bear species. And even ‘non-hibernating’ polar bears may curl up in a snow den for weeks, perhaps months, during winter: at high latitudes, some non-pregnant female bears have had radio locations become static for up to several months during winter before they start moving again”
One of the reasons for this may be due to the fact that while the winters are particularly harsh, that can actually be beneficial to them. The frigid temperatures mean that the sea ice is expanding, giving polar bears more stable places from which to hunt. They often take advantage of that new ice to stalk their favorite prey, seals, from above.
As the temperatures take a turn, bears can do even more hunting since that is the time of year when seal pups are born. The ice may be starting to melt, but this is when polar bears need to hunt as much as possible to add on a thick layer of fat that will help them to survive the rest of the year, so they can’t very well hibernate during the spring or early summer.
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During the summer, the bears don’t get nearly as much food and are often forced to forage for the few berries and bird eggs that they can find. Even still, they have not evolved to ‘opt out’ of the summer months by hibernating. Dr. Whiteman said:
“There doesn’t seem to be enough natural selection pressure for them to completely ‘opt out’ of either summer or winter.”
So, to put it simply, there just isn’t a need for polar bears to have ever evolved to need to hibernate. Even during the times when hunting is at its most difficult, survival has apparently been easier for bears who continued to stay at least somewhat active, and that is likely to continue into the future.
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