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Polar bears are unlikely to physiologically compensate for extended food deprivation associated with the ongoing loss of sea ice, according to one-of-its-kind research. The loss of sea ice in the Arctic, which is outpacing predictions, has raised concern about the future of polar bears, leading to their listing as a globally threatened species under the U.
S. Endangered Species Act in 2008. The bears depend on hunting seals on the surface of the sea ice over the continental shelf, most successfully from April to July. In parts of the polar bears’ range, the lengthening period of sea ice retreat from shelf waters -- caused by increasing temperatures -- can reduce their opportunities to hunt seals, leading to declines in bear nutritional condition. Some earlier research suggested that polar bears could, at least partially, compensate for longer summer food deprivation by entering a state of lowered activity and reduced metabolic rate similar to winter hibernation -- a so-called “walking hibernation.” But the new research shows that the summer activity and body temperature of bears on shore and on ice were typical of fasting, non-hibernating mammals, with little indication of “walking hibernation.”Image credit: Shawn Harper, University of Alaska Fairbanks
