Researchers following a group of adult polar bears found a 45 percent mortality rate among the cubs of those adults that swam 30 miles (48 kilometers) or more at a time, as compared with an 18 percent mortality rate among the cubs of other polar bears. And the rapid loss of sea ice is forcing these longer swims, the scientists said.
"This research is the first analysis to identify a significant multi-year trend of increased long-distance swimming by polar bears," study researcher Geoff York, a World Wildlife Fund polar bear expert, said in a statement. "Prior research had only reported on single incidents." [Gallery: Polar Bears Swimming in the Arctic]