Nyctea scandiaca (Nyctea: Greek, “nocturnal,” referring to owls in general; scandiaca: Latin, Scandinavia)
None recognized; no geographical variation noticed even in specific dimensions, such as wing length.
Circumpolar, north of the tree line, in areas inhabited by lemmings and voles. Nomadic, following food supply, and will wander regularly in North America as far south in US as line drawn from northern third of Oregon, through northern border of Nebraska, through northern third of Illinois and Indiana, to northern half of New Jersey. In heavy incursion years, vagrants can be found as far south as Florida.
In summer, on open arctic tundra that is peppered with rocky outcrops in areas usually corresponding to distribution of lemmings and other rodents. In winter, during their southern wanderings, they can be found in prairies, fields, marshes, on beaches, broad river banks, dunes, and even around airports and on golf courses, again depending upon the availability of food.
In summer, preys chiefly on lemmings and other arctic rodents; also regularly hunts hares and ptarmigan. When rodents are scarce, ducks, alcids, and small songbirds are also taken. During winter incursions, they are opportunistic, and will catch any available prey, including the above mentioned species, plus muskrats, grebes, gulls, coots, pheasant, grouse, quail, waders, hawks, smaller owls, and ravens. Rarely sits in trees; mostly hunts from exposed sites, such as rocky outcrops, dunes, low stumps, fence posts, telephone poles, haystacks, and buildings. Will also search for prey in manner of large Buteo, flying low, sometimes hovering. Has been observed ground hunting by walking, or hopping, over the snow, listening for prey immediately below the surface.
May-June. Nests on ground in slight depressions, sometimes lining thinly with grass, feathers, or moss. Favors high, well-drained sites, such as gravel banks, rocky ledges, and even boulders, all with wide view and usually unsheltered by wind. Clutch is 3 – 9 eggs, as many as 14 in prey boom years.
In North America, adult birds regularly migrate south of zone of 24-hour darkness. More southerly incursions are erratic and irruptive, and often depend upon availability of food in the north.
In North America, seemingly stable, since its breeding range is well out of contact with the influence of civilization; however, hard to measure with scientific certainty because of its unpredictable wintering wanderings. In Europe, population has decreased, perhaps because of long-term changes in climate.