In the previous post I talked about a possible effect of climate change on Polar Bear fitness. Climate change could also have an effect on the reproductive success of Polar Bears. In October or November pregnant female Polar Bears make a snow den on mountain slopes. At the end of the year they normally give birth to twins and they emerge from their den in March or April. At this time the females haven’t eaten anything for about six months and they quickly need something. If they don’t, first one of the cubs will die of starvation, followed by the second. If the bears get to the pack ice and are able to stay there, like this family, they should be fine. Bears stuck on land have a bigger problem, as stated in the previous post.
However, the problem can start already before they get to their dens. On Spitsbergen the most important denning areas are located in the south-east, with large concentrations on Kong Karls Land and Hopen. In some years the ice doesn’t return to these areas until late November. This means the pregnant females have to swim a distance if they want to reach the denning area. Now, even though bears are very good swimmers and this distance doesn’t pose a big problem, it does cost a lot of energy. Energy they also need to raise their cubs. This means less cubs will be born if the sea ice is further away from the denning areas. Data already shows a slight (but not significant) decrease in average number of cubs.
If I look at my own sightings, I can’t remember seeing any mothers with young cubs last year. This would make sense, as the ice was far away in fall 2013. This year it looked a little better. We saw several young cubs, two families with twins and two with single cubs. This could be a result of the better ice conditions last fall, see this image for a comparison between the ice conditions in november 2013 and 2014. Hopefully these families will make it to the ice and have a good winter, so I can see them again next year…
Well written and a good correlation I think. Thanks for bloggning, I enjoy reading your posts.