Dear EarthTalk: I read a heart-wrenching story of a polar bear that swam 400 miles with its cub on its back in search of an ice floe to rest on. It survived but its cub did not. What can be done to save these magnificent creatures? Is it too late?--Jerry Bresnehan, Des Moines, IA
It's sad but true that life is getting harder for polar bears due to global warming. Polar bears live within the Arctic Circle and feed primarily on ringed seals. The bears' feeding strategy involves swimming from the mainland to and between offshore ice floes, poaching seals as they come up to breathe at holes in the ice.
But climate change is heating up the atmosphere and substantial amounts of offshore sea ice are melting. The result is that bears must swim further and further out to sea in search of ice floes; some expend all of their energy in doing so and end up drowning. Scientists first noticed this deadly phenomenon in 2004 when they noticed four drowned polar bears in the Beaufort Sea off Alaska's North Slope.
More recently, researchers from the United States Geological Survey (USGS) fitted several Alaskan polar bears with tracking collars to find out the extent of their travels and document how much trouble they are having hunting in a warmer Arctic. One of the bears, a mother with a yearling cub on her back, made what researchers are calling an "epic journey in search of food" during September-October 2008. "This bear swam continuously for 232 hours and 687 km and through waters that were 2-6 degrees C," reports USGS research zoologist George M. Durner. "We are in awe that an animal that spends most of its time on the surface of sea ice could swim constantly for so long in water so cold." During the rest of the two-month tracking period, the bear intermittently swam and walked on ice floes for another 1,200 miles.
But while the mama bear survived the ordeal, she lost 22 percent of her body fat during a crucial time of year for...