The king eider winters in arctic and subarctic marine areas, most notably in the Bering Sea, the west coast of Greenland, eastern Canada and northern Norway. It also happens yearly off the northeastern United States, Scotland and Kamchatka. Breeding areas include the Arctic coastal tundra of the north coast of Alaska. This species dives for benthic invertebrates, such as crustaceans, polychaete worms, and molluscs, with mussels being a favoured food. Wintering birds can form large flocks on suitable coastal waters, with some flocks bigger than 100,000 birds.