The Pacific loon or Pacific diver (Gavia pacifica), is a medium-sized member of the loon, or diver, family. It may be conspecific with black-throated diver/Arctic loon, which it closely resembles.
It breeds on deep lakes in the tundra region of Alaska and northern Canada as far east as Baffin Island, and in Russia east of the Lena River.
Unlike other loons/divers, this bird may migrate in flocks. It winters at sea, mainly on the Pacific coast, or on large lakes over a much wider range, including China, Japan, North Korea, South Korea, United States and Mexico. It has occurred as a vagrant to Greenland, Hong Kong, Great Britain, Spain, and Finland. source