Most of you probably have some idea of what it is from learning about it in school. And I would guess that the example that comes to mind when you think of an animal that hibernates – especially if you live in North America – is a bear. Am I right? I remember that was the example used when I was in school but it turns out that bears are actually not true hibernators. Surprised?
There are actually different types of hibernation but often science can be thought too complex for the general public (and with good reason sometimes!) so if a term is explained, understood and then used by non-science types, it tends to stick. And for the record, it isn’t wrong – hibernation is the umbrella term for the physiological process - but in recent years more accurate terms have been introduced and are being used more and more.
But let’s start with a definition. Wikipedia defines hibernation as a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. A true hibernator does not wake up during the winter season and due to its lower metabolic rate, lower body temperature and slower breathing, the animal could be mistaken as dead. There is no movement and it takes a long time for the animal to wake up enough to begin moving again. True hibernators are animals like bats, chipmunks, ground squirrels, groundhogs and marmots.
Hibernation is an adaptation to temporary changes in an animal’s environment; in North America it’s associated with winter when an animal’s food source becomes too scarce for it to survive the season. So during the fall, animals that hibernate will eat more food than usual to bulk up so they can live off their extra fat through the winter.
In the case of bears, there are eight different species globally; giant panda, sloth bear, Asiatic black bear, sun bear, spectacled bear, American black bear, brown bear (grizzly) and polar bear. Of these eight species, only four will enter a den during winter months – American black bears, grizzly bears, Asiatic black bears and pregnant female polar bears.
Like a true hibernator, when a bear goes into a den, its heart rate, metabolism and breathing all slow down and they survive the winter months off their fat reserves. The big difference is that bears can and do wake up, and even leave the den for short periods –sometimes looking for food, sometimes stretching their legs. The more specific term for what happens with bears is that they go into a ‘state of torpor’ but because that may sound very complex, when explaining it I say that bears go into ‘a period of dormancy’. Again, they are inactive and live off their fat reserves – like true hibernators – but can wake up and leave the den. If it’s a pregnant female, she won’t leave the den until the spring because she has to stay with her young.
Polar bears are another case altogether. As they live in the Arctic and need the sea-ice from which to hunt seals, they don’t need to go into a period of dormancy in the winter because their food source is abundant. The exception to this, as I mentioned above, is a pregnant female; she enters a den, has her cub(s) and stays put with her young until the spring.
So, question: ‘hibernation’, ‘torpor’ – why does it matter what word is used? I mean, isn’t it just semantics? There are those who would certainly agree with that. But to me, it’s important to know that there is a difference. Many people run, hike and camp during winter months in bear country and may not consider the fact they could encounter one at that time of the year because they were taught bears hibernate for the entire season. In many parts of British Columbia for example, the weather doesn’t get very cold so bears are likely more active during winter months then you might think. I say the more you know, the better prepared you’ll be!
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