Monday, 15 July 2013

Species Spotlight - Snowy Owl


 
The Snowy Owl (Bubo scandiacus) is a large owl of the typical owl family Strigidae. Until recently, it was regarded as the sole member of a distinct genus, but data now shows that it is very closely related to the horned owls.

This yellow-eyed, black-beaked white bird is easily recognizable. It is 52–71 centimetres (20–28 in) long, with a 125–150 centimetres (49–59 in) wingspan. Also, these birds can weigh anywhere from 1.6 to 3 kilograms (3.5 to 6.6 lb). It is one of the largest species of owl and, in North America, is on average the heaviest owl species. The adult male is virtually pure white, but females and young birds have some dark scalloping; the young are heavily barred, and dark spotting may even predominate. Its thick plumage, heavily feathered taloned feet, and colouration render the Snowy Owl well-adapted for life north of the Arctic Circle.

Snowy Owl calls are varied, but the alarm call is a barking, almost quacking krek-krek; the female also has a softer mewling pyee-pyee or prek-prek. The song is a deep repeated gahw. They may also clap their beak in response to threats or annoyances. While called clapping, it is believed this sound may actually be a clicking of the tongue, not the beak.

Young owl on the tundra at Barrow Alaska. Snowy Owls lose their black feathers with age, though particular females retain some.

The Snowy Owl is typically found in the northern circumpolar region, where it makes its summer home north of latitude 60 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.

This species of owl nests on the ground, building a scrape on top of a mound or boulder. A site with
good visibility such as the top of mound with ready access to hunting areas, and a lack of snow is chosen. Gravel bars and abandoned eagle nests may be used. The female scrapes a small hollow before laying the eggs. Breeding occurs in May to June, and depending on the amount of prey available, clutch sizes range from 5 to 14 eggs, which are laid singly, approximately every other day over the course of several days. Hatching takes place approximately five weeks after laying, and the pure white young are cared for by both parents. Although the young hatch asynchronously, with the largest in the brood sometimes 10 to 15 times as heavy as the smallest, there is little sibling conflict and no evidence of siblicide. Both the male and the female defend the nest and their young from predators, sometimes by distraction displays. Males may mate with two females which may nest about a kilometre apart.[3] Some individuals stay on the breeding grounds while others migrate.

Snowy Owls nest in the Arctic tundra of the northermost stretches of Alaska, Canada, and Eurasia. They winter south through Canada and northern Eurasia, with irruptions occurring further south in some years. Snowy Owls are attracted to open areas like coastal dunes and prairies that appear somewhat similar to tundra. They have been reported as far south as the American states of Texas, Georgia, the American Gulf states, southernmost Russia, and northern China.

In January 2009, a Snowy Owl appeared in Spring Hill, Tennessee, the first reported sighting in the state since 1987. More notable is the huge mass southern migration in the winter of 2011/2012, when thousands of Snowy Owls were spotted in various locations across the United States.

This powerful bird relies primarily on lemmings and other small rodents for food during the breeding season, but at times of low prey density, or during the ptarmigan nesting period, they may switch to favoring juvenile ptarmigan. They are opportunistic hunters and prey species may vary considerably, especially in winter. They feed on a wide variety of small mammals such as meadow voles and deer mice, but will take advantage of larger prey, frequently following traplines to find food. Some of the larger mammal prey includes hares, muskrats, marmots, squirrels, rabbits, raccoons, prairie dogs, rats, moles, and smaller birds entrapped furbearers. Birds preyed upon include ptarmigan, other ducks, geese, shorebirds, pheasants, grouse, coots, grebes, gulls, songbirds, and even other raptors, including other owl species. Most of the owls' hunting is done in the "sit and wait" style; prey may be captured on the ground, in the air or fish may be snatched off the surface of bodies of water using their sharp talons. Each bird must capture roughly 7 to 12 mice per day to meet its food requirement and can eat more than 1,600 lemmings per year.

Snowy Owls, like many other birds, 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.

Though Snowy Owls have few predators, the adults are very watchful and are equipped to defend against any kind of threat towards them or their offspring. During the nesting season, the owls regularly defend their nests against arctic foxes, corvids and swift-flying jaegers; as well as dogs, gray wolves and avian predators. Males defend the nest by standing guard nearby while the female incubates the eggs and broods the young. Both sexes attack approaching predators, dive-bombing them and engaging in distraction displays to draw the predator away from a nest. They also compete directly for lemmings and other prey with several predators, including Rough-legged Hawks, Golden Eagles, Peregrine Falcons, Gyrfalcons, jaegers, Glaucous Gulls, Short-eared Owls, Great Horned Owls, Eurasian Eagle Owls, Common Ravens, wolves, arctic foxes, and ermine. They are normally dominant over other raptors although may (sometimes fatally) lose in conflicts to large raptors such as other Bubo owls, Golden Eagles and the smaller but much faster Peregrine Falcons. Some species nesting near Snowy Owl nests, such as the Snow Goose, seem to benefit from the incidental protection of snowy owls that drive competing predators out of the area.

Info courtesy of Wikipedia