Bruce H. Oakley

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‘Hey, lay off my carcass!’ Grizzlies chase polar bears away from important food source

Each autumn, polar bears and grizzly bears are drawn to Kaktovik, Alaska, to dine on the rotting carcasses of bowhead whales. Discards from the town’s yearly hunt, the remains give biologists a unique opportunity to observe ongoing encounters between apex predators. Polar bears have long been portrayed as solitary and aggressive, but at the bone piles they reach a kind of truce. Researchers have observed as many as 20 of them sharing the carcass at once. When grizzlies arrive, the scene changes. Arctic grizzlies are small, but they don’t hesitate to chase away polar bears twice their size, according to a report in the Journal of Mammalogy. Researchers observed 137 interactions between polar and grizzly bears at the bone pile (like the one pictured above, where a grizzly surveys the carcass as a polar bear feeds). In 124 of those meetings, the polar bears fled, sometimes never to return. Because Kaktovik’s polar bears seem especially susceptible to the Arctic’s shrinking sea ice, researchers are concerned they may start relying more heavily on nutrient-poor food from land. If the area’s grizzlies consistently drive polar bears away from bone piles and other feasts, younger bears and nursing females could suffer. The team hopes future research will clarify the impacts of grizzly bear aggression on the polar bear population.