The snowy owl (Bubo scandiacus), also known as the polar owl, the white owl and the Arctic owl, is a large, white owl of the true owl family. Snowy owls are native to the Arctic regions of both North America and the Palearctic, breeding mostly on the tundra. It has a number of unique adaptations to its habitat and lifestyle, which are quite distinct from other extant owls. One of the largest species of owl, it is the only owl with mainly white plumage. Males tend to be a purer white overall while females tend to have more extensive flecks of dark brown. Juvenile male snowy owls have dark markings and may appear similar to females until maturity, at which point they typically turn whiter. The composition of brown markings about the wing, although not foolproof, is the most reliable technique for aging and sexing individual snowy owls.
Most owls sleep during the day and hunt at night, but the snowy owl is often active during the day, especially in the summertime. The snowy owl is both a specialized and generalist hunter. Its breeding efforts and global population are closely tied to the availability of tundra-dwelling lemmings, but in the non-breeding season, and occasionally during breeding, the snowy owl can adapt to almost any available prey – most often other small mammals and northerly water birds, as well as, opportunistically, carrion. Snowy owls typically nest on a small rise on the ground of the tundra. The snowy owl lays a very large clutch of eggs, often from about 5 to 11, with the laying and hatching of eggs considerably staggered. Despite the short Arctic summer, the development of the young takes a relatively long time and independence is sought in autumn.
A ghost of the tundra, hunting in daylight that never ends.
Description
The snowy owl is mostly white. They are purer white than predatory mammals such as polar bears (Ursus maritimus) and Arctic fox (Vulpes lagopus). Often when seen in the field, these owls can resemble a pale rock or a lump of snow on the ground. They usually appear to lack ear tufts but very short (and probably vestigial) tufts can be erected in some situations, perhaps most frequently by the female when she is sitting on the nest. The ear tufts measure about 20 to 25 mm (0.79 to 0.98 in) and consist of about 10 small feathers. The snowy owl has bright yellow eyes. The head is relatively small and, even for the relatively simply adapted hearing mechanism of a Bubo owl, the facial disc is shallow and the ear is uncomplicated. 1 male had ear slits of merely 21 mm × 14 mm (0.83 in × 0.55 in) on left and 21 mm × 14.5 mm (0.83 in × 0.57 in) on the right.
Distribution and habitat
The snowy owl is typically found in the northern circumpolar region, where it makes its summer home north of latitude 60° north though sometimes down to 55 degrees north. However, it is a particularly nomadic bird, and because population fluctuations in its prey species can force it to relocate, it has been known to breed at more southerly latitudes. Although the total breeding range includes a little over 12,000,000 km2 (4,600,000 sq mi), only about 1,300,000 km2 (500,000 sq mi) have a high probability of breeding, i.e. breeding at no more than 3–9-year intervals. Snowy owls nest in the Arctic tundra of the northernmost stretches of Alaska, Northern Canada, and the Euro-Siberian region.
Diet and hunting
Snowy owls may hunt at nearly any time of the day or night, but may not attempt to do so during particularly severe weather. During the summer solstice, the owls appear to hunt during "theoretical nightfall". Night-vision devices have allowed biologists to observe that snowy owls hunt quite often during the extended nighttime during the northern winter. Prey are both taken and eaten on the ground. Like other carnivorous birds, Snowy owls often swallow their small prey whole. Strong stomach juices digest the flesh, while the indigestible bones, teeth, fur, and feathers are compacted into oval pellets that the bird regurgitates 18 to 24 hours after feeding. Regurgitation often takes place at regular perches, where dozens of pellets may be found. Biologists frequently examine these pellets to determine the quantity and types of prey the birds have eaten. When large prey are eaten in small pieces, pellets will not be produced. Larger prey is often torn apart, sometimes including removal of the head, with the large muscles, such as the humerus or breast, typically eaten first. The scattering of remains that results from the increment feeding on larger prey is thought to result in under-identification of them compared to smaller prey items.
Behavior
Snowy owls may be active to some extent at both day, from dawn to dusk, and night. Snowy owls have been seen to be active even during the very brief winter daytime in the northern winter. During the Arctic summer, snowy owls may tend to peak in activity during the twilight that is the darkest time available given the lack of full nightfall. Reportedly, the peak time of activity during summer is between 9:00 pm and 3:00 am in Norway. The peak time of activity for those owls that once nested on Fetlar was reported between 10:00 and 11:00 pm.
Breeding
In Utqiaġvik, of 239 recorded breeding attempts, 232 were monogamous, the other 7 social bigamy. On Baffin Island, 1 male bred with 2 females and sired 11 total fledged young. Another case of bigamy was reported in Norway where the 2 females bred to one male were 1.3 km (0.81 mi) apart in nest site location. On Fetlar from 1967 to 1975, a male bred with two females, 1 younger and was possibly his own daughter. In the Fetlar males first time breeding with both females, he did not bring food to the younger female. However, when older female disappeared the following year, the male and younger female producing 4 young, but disappeared the subsequent year altogether in 1975. There are also unconfirmed cases of polyandry, with 1 female being fed by 2 males. Snowy owls can breed once per year but when food is scarce many do not even attempt to breed.