The Arctic Loon is a widely distributed species that breeds on freshwater lakes and ponds in Arctic and Subarctic regions across Eurasia, extending east to westernmost Alaska. After breeding, individuals move south and towards the sea, wintering primarily in sheltered coastal areas of the northeastern Atlantic, south as far as Mediterranean, Black Sea, Caspian Sea, and the western Pacific south to China and Japan. Arctic Loon is a rare visitor along the Pacific Coast of North America and even rarer at large inland lakes.
The nomenclatural history of the Arctic Loon is closely linked with its nearest relative, the Pacific Loon (Gavia pacifica), with which it has been considered conspecific at various times in the past. Since 1985, the American Ornithologists' Union has recognized the Arctic Loon and Pacific Loon as distinct species (1), based in part on sympatric breeding in northeastern Asia and western Alaska. However, because these species were combined for much of the 1900s, much of the literature on the Arctic Loon was published under the name Pacific Loon (as G. a. pacifica). The Arctic Loon is comprised of two subspecies, a widespread Eurasian race, G. a. arctica (the Black-throated Loon or Black-throated Diver) to which most older studies pertain, and a Siberian race, G. a. viridigularis (the "Green-throated" Loon), whose breeding distribution extends marginally eastward to western Alaska.
Although many studies have examined the ecology of the Arctic Loon across much of Eurasia, most published research pertains to European and western Asian populations, with those breeding in northeastern Siberia and western Alaska receiving little attention from researchers. Owing to the species' rarity and remote breeding range, the Arctic Loon is among the least studied regular breeding species in North America. This account summarizes available information on G. a. viridigularis in North America, the only subspecies known to occur (based on specimens). Also included is selected information from studies of Eurasian populations that may be applicable to the North American population. For details of the more extensive work on Arctic Loon across Eurasia, readers should consult Witherby et al. (2), Lehtonen (3), Cramp and Simmons (4), Sjölander (5), and del Hoyo et al. (6).