Wednesday, May 11, 2011

White Bear, RIP?

kw: book reviews, nonfiction, natural history, animals, bears

This image (© Monado) is used at for their article on the effects of global warming on polar bears. It does seem quite evocative. Truth to tell, though, the article is short and hortatory rather than explanatory.

For explanation, read The Great White Bear: A Natural & Unnatural History of the Polar Bear by Kieran Mulvaney. The nine chapters in this book present a through summary of the natural history of polar bears, and it becomes clear that his message is the "unnatural history", the story of polar bears' interactions with humans and the human world, and particularly the changing climate, to whatever extent we are responsible for that.

Consider a predator, an obligate carnivore, that can weigh 3/4 of a ton, stands as tall as 13 feet (4m) and has been known to prey on beluga whales. The only seal it is reluctant to tackle is the walrus. Its primary prey is the ringed seal, which is the size of a smallish man or average woman. We "two-legged seals" are just another prey animal, except that we have too little blubber, but we do have guns. This bear moves through its world with the confident swagger of an emperor. If Terry Bisson's semisweet story "Bears Discover Fire" is ever realized, our own status as top predator on the planet will be seriously in jeopardy.

Female bears are about half the size of the males, which do a lot of fighting over them. But the female has to fatten up the most, not to over-winter, but to "over-summer". All polar bears fast for about four months when the ice is offshore and seals cannot be had. Females have the added requirement to nurse cubs in a den dug into the permafrost or icebound snow, for another 3-4 months, fasting all the while. Sometimes the fast lasts eight months. How much would you have to eat, from May to July, if you knew your next meal would be in April? It is no surprise that polar bears are a bit testy while they await ice-up.

This underlies the extreme caution people learn if they live at Churchill, Manitoba, the "Bear Capital of the World". This odd little town sits right on a bear migration route, near an area where they gather while awaiting the November freeze-up. If you meet a polar bear in Churchill in the Fall, and it hasn't eaten since July, guess who is most likely to survive the encounter!

The message the author brings after his chapter on Churchill, though, is that the bears are fasting longer and getting leaner each year. It has been going on for a couple decades at least. The polar bear is really an ice bear. The sea ice in the Arctic is steadily reducing, and if it goes completely, the populations of several animals will crash, including the polar bear and several species of seal, plus the ice-edge ecosystems that supply food to those seals and the fish they eat. A world without polar bears will probably also be a world without walruses.

I think back to the Medieval Warming that occurred between 950 and 1250 A.D. There is some disagreement over whether it was warmer than the present warming, but it was certainly longer (so far; we have 300 years to go). How was the Arctic ice affected in those years? Somehow polar bears survived. It would be instructive to determine if their genetic variability, or lack thereof, would indicate a genetic bottleneck some 1,000 years in the past. So far as I know such a study has not been done.

Whether you believe we are primarily responsible for the current climate change, or only partially responsible (my own position), or not at all, it is a fact that climate is changing and polar bears are being seriously impacted. Author Mulvaney presents a clear and eloquent explanation of just how the bears' livelihood is linked to the timing of sea ice expansion and retreat. The changes seem to be happening too fast for evolutionary changes to allow the bears to adapt effectively. If polar bears survive the 21st Century, those of the coming century will be rather different than the bears of today. Less dependent on particular timings of ice, perhaps having learned to exploit a wider range of prey, they will be as well-adapted as they can be to the conditions they must live with, or die from.

Will the polar bear become extinct in the 21st Century? It is most likely that some of the twenty populations of polar bears will vanish. This assumes that some refugia of sea ice will remain. If all the sea ice goes, year round, then it is likely that no bears will survive. That is a sad prospect.

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