The great grey owl (Strix nebulosa), also known as the great gray owl in American English, is the largest species of owl in the world based on length. It is found across the Northern Hemisphere and is the only species in the genus Strix that is present in both the Eastern and Western Hemispheres. In certain regions, it is referred to as the Phantom of the North, cinereous owl (a name also used for S. sartorii), spectral owl, Lapland owl, spruce owl, bearded owl, or sooty owl.
Description
The great grey owl has a distinctive appearance, with a large, rounded head, a grey face, and yellow eyes circled with dark feathers. Its underparts are light with dark streaks, while its upper parts are grey with pale bars. Unlike many other owl species, it lacks ear tufts but has the largest facial disc of any raptor. There is a white collar or “bow-tie” just below its beak, and its long tail tapers to a rounded end.
The great grey owl is known as the world’s largest species of owl based on length, surpassing even the Eurasian eagle-owl and the Blakiston’s fish owl.[citation needed] However, it is outweighed by several other species, including most of the genus Bubo, due to its light body and fluffy feathers. Females are larger than males, with an average length of 72 cm (28 in) compared to 67 cm (26 in) for males. The wingspan can exceed 152 cm (5 ft 0 in), but typically ranges from 140 to 142 cm (4 ft 7 in to 4 ft 8 in) for males and females, respectively. Adult weight ranges from 580 to 1,900 g (1.28 to 4.19 lb), with females averaging 1,290 g (2.84 lb) and males averaging 1,000 g (2.2 lb).[5]
The great grey owl’s call is a series of deep, rhythmic ‘who’s that is usually heard during territorial or offspring interactions. Adults are typically silent at other times. The young may chatter, shriek, or hiss, while tame owls may produce higher-pitched hoots when given food by humans.
Taxonomy
The great grey owl is distributed across North America and Eurasia and is recognized as two distinct subspecies.[6] S. n. nebulosa (Forster, 1772) inhabits North America, ranging from central Alaska across Canada to southwestern Quebec, and south to northern California, northern Idaho, western Montana, Wyoming, and northeastern Minnesota. Meanwhile, S. n. lapponica (Thunberg, 1798) is found in northern Eurasia, from Fennoscandia through Siberia to Sakhalin and Kamchatka Krai, and also in Lithuania, Lake Baikal, Kazakhstan, Mongolia, Manchuria, and northeastern China.
Habitat
The great grey owl typically breeds in dense coniferous forests of the taiga in northern regions, often near open areas like meadows or bogs. However, in Oregon and California, this species has also been observed nesting in mixed oak woodlands. While it was once believed that the great grey owl required a cold climate, it is now known that this bird can survive in a few areas where summer temperatures can exceed 100°F (38°C).
Range
The great grey owl is a bird that breeds across North America and northern Eurasia. In North America, their breeding habitat ranges from Quebec to the Pacific coast and Alaska. In Europe, they breed in Norway, Sweden, Finland, and Russia. Despite occurring in Europe, the first great grey owl scientifically recognized was found in Canada in the late 18th century.
These birds are permanent residents, although populations in the north may move south and southeast in search of food when resources are scarce. They are found in disjunct areas of appropriate habitat in the Pacific states of California, Oregon, and Washington, with sedentary populations in these regions. In winter, they may move downslope to avoid deep snow and capture prey on the ground.
In Oregon, their breeding range is scattered from the Siskiyou Mountains in the southwest to the Blue Mountains in the northeast. Two bird festivals each May feature field trips to try to spot the species. The Ladd Marsh Festival in La Grande, OR and the Mountain Bird Festival in Ashland, OR.
The great grey owl is listed as Endangered under the California Endangered Species Act, with fewer than 300 birds estimated in California in 2015. Their range in California includes a small extension of the Oregon population, as well as breeding sites in the Tahoe National Forest, the Sierra Nevada foothills, and Yosemite. A study of the Yosemite population revealed they have been genetically isolated from populations in Oregon and farther north for more than 25,000 years. Biologists suggest that the Yosemite population should be considered a separate sub-species, Strix nebulosa yosemitensis. In Washington state, only a handful of great grey owl nests have been found in the southeast in the Colville National Forest.
In the western United States, they breed in Idaho, Montana, and Wyoming, as far south as the Grand Teton and Yellowstone National Parks. In northeastern North America, great grey owls are found year-round in southern Quebec and Ontario, with individuals sometimes moving further south in winter into New York and New England in search of more abundant prey. They are rarely sighted as far south as Pennsylvania and Long Island, New York, but in winter 2017, the birds were recorded in northern New York in Robert Moses State Park and central Maine.
Breeding
Great grey owls typically do not build nests and instead use nests previously used by large birds such as raptors. They may also use broken-topped trees and cavities in large trees. In Oregon, the great grey owl has been using man-made platforms for nest sites since the 1980s. Nesting usually occurs from March to May, and four eggs are the usual clutch size. The incubation period lasts about 30 days, and brooding lasts 2 to 3 weeks. After this, the young will jump or fall from the nest at 3 to 4 weeks and start to fly 1 to 2 weeks after that. The young owls will remain near their natal sites for many months after fledging.
The great grey owl’s reproduction is connected to the fluctuations of small mammal populations, and in years when food is scarce, they may travel far to find prey. They are not migratory but may be nomadic. In one case in Oregon, a landowner named Andy Huber helped a female great grey owl raise her four nestlings after the male was killed by a great horned owl. Huber live-trapped small mammals and released them at the nest site for the female to bring to the nestlings. Huber and the mother owl successfully raised all four owlets.
Feeding
Great grey owls use a variety of techniques to hunt for prey, including waiting, listening, and watching before swooping down on their prey. They may also fly low through open areas in search of prey. Frequently, they hunt from a low listening post such as a stump, low tree limb, fence post, or road sign. Their large facial discs, or “ruffs”, focus sound, and the asymmetrical placement of their ears assists them in locating prey during the late and early hours when there is little light. They are primarily nocturnal and are most active during the night. On nesting grounds, they mainly hunt at night and near dawn and dusk.
Great grey owls have excellent hearing and can locate and capture prey moving beneath 60 cm (2.0 ft) of snow in a series of tunnels solely with that sense. They then crash to a snow depth roughly equal to their own body size to grab their prey. This species and, more infrequently, other fairly large owls from the genus Strix are known to “snow-plunge” for prey, a habit that is thought to require superb hearing not possessed by all types of owls.
Unlike the more versatile eagle and horned owls, great grey owls rely almost fully upon small rodents. The species primarily feeds on the most abundant and available small mammals. In northern Canada and other parts of Scandinavia, they primarily eat lemmings, while in dry parts of California’s Sierra Nevada, they eat mostly pocket gophers. In some areas, voles are the predominant prey. Occasionally, they feed on alternative prey animals such as hares, moles, shrews, weasels, thrushes, grouse, Canada jays, mountain quail, small hawks, and ducks, but this makes up less than 20% of their prey intake. They do not scavenge or steal from other predators. In mated pairs, the male is the primary hunter who provides food for the entire family, while the female guards and broods the eggs, nestlings, and flightless fledglings.
Overall, great grey owls have adapted well to their environments and have developed unique strategies for finding and capturing prey. Their superb hearing, combined with their hunting techniques, makes them highly efficient hunters.
Threats
The great grey owl is facing many threats, with the most significant being the harvesting of timber from their habitat. Timber management practices typically remove the large-diameter trees used for nesting, the leaning trees used by juveniles for roosting, and the dense canopy closures used by juveniles for cover and protection. If perches are not left in clearcuts, the owls cannot hunt in them, which is essential to their survival. The species is more commonly found in areas protected from logging, although human-made structures designed for their use have been utilized.
Livestock grazing in meadows is also harmful to great grey owls as it reduces the habitat for preferred prey species. Other dangers include rodenticides, collisions with vehicles, and the West Nile Virus. The virus is likely to become more prevalent with climate change, and there have been confirmed great grey owl deaths from the virus in Ontario and northeastern Oregon. Evidence of the virus has also been found in the Yosemite area since 2005.
Despite their large size, the great grey owl has few natural predators. Predators that pose a threat to young include great horned owls, various small carnivores, and black bears, but they rarely threaten adults. The owls have been known to fend off animals as large as black bears when defending their nests. The only known predator of adult great grey owls is the Eurasian eagle-owl, which occasionally preys on them in parts of Europe.
Territorial behavior
The great grey owl is a unique predator, known for being less aggressive than other large predatory birds. Unlike other alpha predators, they are less likely to attack each other or perceived threats. Great grey owls do not defend a large nesting territory, nor do they protect their hunting territories through aggression. However, the female is an exception and can be aggressive in protecting her eggs and owlets. She is particularly vigilant and fierce when fledglings first leave the nest but are still unable to fly, as they are vulnerable to potential predators.
Due to their lack of territorial aggressiveness, great grey owls are challenging to locate in the wild. Most owls respond to calls of their own species when played back in a nesting territory. However, great grey owls often ignore such calls. They also do not fly away every time a human approaches or drives past. Instead, they often remain still even if a human is nearby, which means they are frequently overlooked or unnoticed.
This owl’s behavior makes them vulnerable to threats, such as habitat destruction, rodenticides, vehicle collisions, and the West Nile Virus. Their nests are also susceptible to destruction from logging activities that reduce live and dead large-diameter trees used for nesting and leaning trees used by juveniles for roosting. Moreover, grazing livestock in meadows can reduce the habitat for the great grey owl’s preferred prey species.
Despite their relatively peaceful nature, great grey owls have few natural predators due to their large size. Occasionally, great horned owls, various small carnivores, and black bears prey on young owls. However, these predators rarely threaten adult great grey owls. The only known predator of adult great grey owls is the Eurasian eagle-owl, which occasionally preys on them in parts of Europe.
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