Polar bears typically hunt seals out at sea, returning to land when springtime temperatures melt the ice floes the bears use as rest stops. But climate change has been causing sea ice to melt earlier each year (pictures), forcing polar bears to come ashore sooner.

(See "Most Polar Bears Gone By 2050, Studies Say.")

In a previous study, biologist Robert Rockwell and his colleague Linda Gormezano documented polar bears in Canada's Hudson Bay area (map) returning to land about two weeks earlier than they'd done in the past, near the end of June instead of the middle of July.

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