The snowy owl (Bubo scandiacus) is a bird of prey from the family Strigidae, and found throughout much of the Arctic tundra. Regarded for a long time as the only species of the genus Nyctea and therefore considered taxonomically isolated from the other species of owls, recent molecular studies have shown that it belongs to the genus Bubo, and is closely related to the great horned owl (Bubo virginianus). The external differences, such as the white plumage color and the feathered feet and toes, can be explained as adaptation to the arctic habitat.
The snowy owl is large, nearly as large as the Eurasian eagle owl (Bubo bubo). Adult birds have a length of 21.6 to 25.9 inches, a wingspan of 57 to 61.8 inches, and weigh between 3.52 and 5.5 pounds; females are slightly larger than males.
The plumage is all white marked by brownish or black barring on individual feather tips. Adult females show a heavy amount of these bars; in contrast, adult males are nearly all-white. The face and upper portion of the chest on both is white. The black beak is mainly covered by dense, fine white feathers. The iris of the eyes is golden yellow. Similar to other members of genus Bubo, snowy owls also have ear tufts, but they are markedly less pronounced and are rarely erected. The feet and toes are tightly feathered in dense, snowshoe-like feathers, which serve as heat insulation and prevent the owl from sinking into the snow.
Snowy owls are very silent outside the brewing season. During the breeding season, on the other hand, the male emits a loud, rough croaking and a deep barking "hu", which is used to attract females and can be heard on the tundra over several miles. During this time, the female occasionally makes a croak, which is loud, but much quieter than the male. The birds calls also include hissing sounds, with which the youngsters use on the parent birds for food, cackling "ka ka ka" calls as warning calls, and a mule-like "kjaa" call if disturbed during the breeding.
Range and habitat
Snowy owls have a circumpolar distribution and occur in the tundra areas of Iceland, Northern Europe, Siberia, Alaska, Canada and Greenland. The southernmost deposits, for example in Norway, are found in mountains. From 1967 to 1975, snow-owls brooded on the Shetland Islands.
The snowy owl is a so-called "survival migrant" within its range, that is, it will adapt to the available food supply. Their occurrence in an area is dependent on the fluctuations in the stocks of the lemmings, their main prey. In very cold, snowy winters, or after a collapse of the lemming population, snowy owls migrate southward to Central Russia, Central Asia, Manchuria and the northern United States; occasionally, they also come to the north of central Europe.
The snowy owl lives on clear terrain north of the treeline in the high Arctic. In the Arctic they overwinter in wind-swept, snow-cleared areas of the tundra; in Scandinavia mainly in the mountains. Breeding areas are small patches of elevated ground, in areas which are free of snow early. Owls that have migrated southward often stay and hunt on agricultural land.
Snowy owls hunt from a still position, and since the tundra is generally featureless they scan the area from a rock, a small mound jutting above the landscape, or a stump. The attack is a quick flight and glide, and like other owls it is silent. The spread feathers on wings and tail, in addition to the feathers on the feet, prevent the owl from sinking in soft snow.
The snowy owl is an opportunist hunter, taking as prey whatever is available in the high Arctic. Prey usually consists of small mammals such as mice, but mainly from lemmings; it will also take arctic hares, ptarmigan, ducks, gulls, and fish.
Snowy owls prefer areas with numerous crags, protrusions and small hills. The female digs an earthen trough in an elevated, snow-free place and, depending on the food supply lays 3 to 11 eggs, with each egg laid at every other day. The female alone incubates the eggs, the male supplying her with food. After about one month, the young birds hatch, again at 2-day intervals, with the result of age differences within the brood. If there is not enough food for all chicks, younger and smaller chicks die first. After about 6 to 7 weeks after hatching the young birds are fledged.