Polar Bears - Data, Pictures and Videos

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From the facebook page of Dr. Thea Bechshoft, A Polar bear expert and researcher , On her page she take and answer on any question related to polar bear. Below is a question asked by Geoffrey.

Question from Geoffrey: "Do polar bears hibernate and if yes, how long? Does it depend on which area they live in? And will climate change be a problem?"

Answer by Dr. Thea Bechshoft: Even though some bears hang out in old dens for brief periods during especially nasty snow storms, pregnant females are the only polar bears that hibernate. All other polar bears are active, hunting on the sea ice throughout the winter.

While the other polar bears are out in the cold and dark of winter, the pregnant female will stay in her den, lowering her body temperature and heart rate. By lowering her metabolism, she can reduce the energy she needs to survive by an impressive 60%. As a pregnant female polar bear can be in her den for up to 8 months without eating or drinking being able to survive only by metabolizing her own body fat is an essential physiological ability. Especially since she is not just keeping herself alive off of her own bodily reserves, but must also convert the majority of her fat into milk for her cub(s). The female’s time in the den is generally made up of 2-4 months alone prior to giving birth, and 3-4 months together with her new-born cub(s), nursing. After leaving the den, the family head out towards the ice, looking for seals.

There is a tendency for the more southern-living polar bears to enter and leave the den earlier than those living further north, but if I were to give an “average” it would be October-March (with variations of up to a month or so on either side of this time period). However, the timing of entering into or leaving the den also depends on many other factors – female body condition, female age and experience, weather, growth of the cub(s), snow accumulation, ice condition etc. - and so varies between individual females as well as between years.

Climate change is likely to lead to a number of challenges for the pregnant and hibernating females. First of all, lack of sea ice ultimately leads to worse seal hunting conditions and thus thinner polar bears. A pregnant female in poor body condition is more likely to stay on the ice longer, hoping for extra seals - in other words, she is likely to enter the den at a later point in the year than a heavier female would. In addition, females in poorer body condition have smaller cubs and also have a tendency to leave the den earlier, which can be fatal to the cubs, if they are not yet grown and robust enough for the outside world. Another consequence of climate change is an increase in rain events in the Arctic. Rain changes the texture of snow, which could e.g. make it harder for the pregnant female to find a suitable spot to dig her den and/or cause the den to collapse as the snow roof gets saturated and heavy with rain. Finally, the changing sea ice conditions seem to be causing a shift in where the pregnant females are denning: in areas where they used to den on the ice, they now den on land and in areas where they used to den on land, they are now denning on the ice. Ongoing studies will tell us more about this particular change in the bears’ denning ecology in the years to come.

The picture here shows a female polar bear with her two cubs at their den on the shore of Western Hudson Bay. The family group will often stay near the den for a week or two after their first emergence before finally heading out to the sea ice to look for seals.

*This image is copyright of its original author

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