Polar bears inhabit the circumpolar regions of the U.S., Russia, Canada, Norway, and Denmark. They exist in the most extreme environment for all bear species. Like the desert, environmental factors change very quickly in the Arctic and can be highly variable. When prey is plentiful, polar bears must hunt as much as possible to store adequate body fat to support them for the periods of time when prey is unavailable, and during the females’ winter denning period. Polar bears are so well adapted to their frigid habitat with thick fur, tough skin, and a thick layer of body fat, that they are likely to overheat during running or other vigorous activities. Since they are so well insulated and only have a few places to dissipate heat (paws, mouth, and nose), swimming is one of the best ways for a polar bear to cool off. That’s why on hot days you can often see the San Diego Zoo’s three polar bears in the pool having fun!
Polar bears are a top predator in the Arctic food web. Their place at the top influences populations that are lower in the web, including their main prey species, the ringed seal. Furthermore, their feeding habits influence several scavenger species, such as the Arctic fox and ivory gull, that are dependent on the seal scraps that may get left behind after a kill. The loss of a top predator in an ecosystem typically has a negative affect resulting in trophic cascades and disease prevalence, exemplified by the removal of wolves from Yellowstone National Park.
Polar bears are completely dependent on their sea-ice environment for survival, and as climate change reduces the amount of yearly sea ice formation, their future is uncertain. Annual sea ice is breaking up earlier and forming later, which means shorter hunting seasons, less body fat, and an increase in cub mortality. More open water between ice flows and an increase in females denning up on the mainland over winter has been observed. Many bears now spend more time on the mainland and are forced to seek out different food sources. However, the best science suggests that opportunistic feeding on birds, lichen, even caribou, is not enough to support the polar bear: it needs the ice and the seals!
The sea ice may help polar bears find mates, too. During the spring before the ice breaks up, these bears with vast and wide home ranges manage to mysteriously find each other out on the ice. Polar bears have home ranges (about 25,000 square miles or 65,000 square kilometers) that vary from year to year. They don’t have rigid territories like other bear species but instead have distinct and predictable home ranges, which they scent mark to advertise their presence. For instance, if you stopped by the giant panda exhibit a month ago, you would have seen Bai Yun or Gao Gao scent marking the ground, rocks, branches, or even doing handstands to mark trees. However, in the polar bear’s habitat at breeding time there are only vast stretches of sea ice, so that is where they leave their scent as they walk. Female polar bears only breed once every three years, yet researchers have seen males sniff tracks in the snow and then follow them for miles and miles to an available female. How do they do that and not waste a lot of time and energy to find the right bear?
Here at the San Diego Zoo Institute for Conservation Research, we have been studying how polar bears accomplish this. As it turns out, they passively track scent on the snow with every step, and during breeding season they can tell if a footprint is from a male or female and if the female is in estrus or not. Who knew toe jams communicate so much about a polar bear? So what will happen if the sea ice melts and the scent trails are lost or broken? Further fragmentation among subpopulations is a concern, and more bears may fail to reproduce because they simply cannot find a mate.
However, while there are reasons for hope, we need to continue to make conservation strides in order to improve the situation for the polar bear! In 2008, the polar bear was officially listed as threatened under the U.S. Endangered Species Act, which should afford them greater protections. However, according to Polar Bears International Scientist Dr. Steven Amstrup, the recent status report that indicated that 3 of the 19 subpopulations of polar bear were stable “compares negatively” with the assessment done in 2005 (where 5 subpopulations were stable) and is in even more striking contrast to 2001 (when only 1 subpopulation was in decline).
This Bear Awareness Week I encourage you to do something proactive on behalf of bears and the issues that affect them. Reducing your carbon footprint is vital to helping polar bears. It sounds silly for the most carnivorous bear, but I am going vegetarian at lunchtime this week to reduce my carbon footprint. There are many simple ways to help polar bears: try putting your on the laundry line, recycling is always important, and walking/biking or even getting a tune-up on your car can help. For more information on ways to help or to get more involved with issues that affect polar bears, visit Polar Bears International.
Christine Slocomb is a research technician at the San Diego Zoo Institute for Conservation Research.
Read more about San Diego Zoo Global’s conservation work with bears…
To help bears and other animals, join our Global Action Team!
Watch the Zoo’s polar bears daily on Polar Cam.