Great grey owl | |
---|---|
Strix nebulosa | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Strigiformes |
Family: | Strigidae |
Genus: | Strix |
Species: | S. nebulosa |
Binomial name | |
Strix nebulosa Forster, 1772 | |
The great grey owl (Strix nebulosa) (also great gray owl in American English) is a true owl, and is the world's largest species of owl by length. It is distributed across the Northern Hemisphere, and it is the only species in the genus Strix found in both Eastern and Western Hemispheres. In some areas it is also called the Phantom of the North, cinereous owl (this name is also used for Strix sartorii ), spectral owl, Lapland owl, spruce owl, bearded owl, and sooty owl. [3]
Adults have large rounded heads with grey faces and yellow eyes with darker circles around them. The underparts are light with dark streaks; the upper parts are grey with pale bars. This owl does not have ear tufts and has the largest facial disc of any raptor. There is a white collar or "bow-tie" just below the beak. The long tail tapers to a rounded end.
In terms of length, the great grey owl is believed to exceed the Eurasian eagle-owl and the Blakiston's fish owl as the world's largest owl. [ citation needed ] The great grey is outweighed by those two species as well as several others, including most of the genus Bubo . [4] Much of its size is deceptive, since this species' fluffy feathers, large head and the longest tail of any extant owl obscure a body lighter than that of most other large owls. The length ranges from 61 to 84 cm (24 to 33 in), averaging 72 cm (28 in) for females and 67 cm (26 in) for males. The wingspan can exceed 152 cm (5 ft 0 in), but averages 142 cm (4 ft 8 in) for females and 140 cm (4 ft 7 in) for males. The adult weight ranges from 580 to 1,900 g (1.28 to 4.19 lb), averaging 1,290 g (2.84 lb) for females and 1,000 g (2.2 lb) for males. [5] The males are usually smaller than females, as with most owl species. [3]
The call of the adult is a series of very deep, rhythmic 'who's, which is usually given in correlation to their territories or in interactions with their offspring. At other times, adults are normally silent. The young may chatter, shriek, or hiss. Tame owls may produce higher-pitched hoots when given food by humans.
There are two recognized subspecies of the great grey owl spread across North America and Eurasia. [6]
In northern areas their breeding habitat is often the dense coniferous forests of the taiga, near open areas, such as meadows or bogs. In Oregon and California this owl has been found nesting in mixed oak woodlands. Once believed to require a cold climate, it is now known that this bird survives in a few areas where summer temperatures exceed 100 °F (38 °C).[ citation needed ]
They breed in North America from as far east as Quebec [3] to the Pacific coast and Alaska, and from Finland and Estonia across northern Asia. They are permanent residents, although northerly populations may move south and southeast when food is scarce. In Europe they are found breeding in Norway and Sweden and more numerously through Finland and Russia. Even though the species occurs in Europe, the first great grey owl recognized by science was found in Canada in the late 18th century.
There are sedentary populations in the Pacific states of California, Oregon, and Washington. The great grey owl in this region is found in disjunct areas of appropriate habitat. In winter these birds do not move far but may go downslope to escape deep snow as they must capture their prey on the ground.
In Oregon, the great grey owl 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 see the species: The Ladd Marsh Festival in La Grande, OR and the Mountain Bird Festival in Ashland, OR.
A 2015 study in California estimated there were fewer than 300 birds in the state at the time. The species is listed as Endangered under the California Endangered Species Act. [7] [ full citation needed ] The California range for the species includes a small extension of the Oregon population, north of Alturas. In addition breeding has been confirmed in the Tahoe National Forest east of Nevada City; in the Sierra Nevada foothills south of I-80 at around 2,000 feet (610 m) elevation; and for the population clustered around Yosemite. In Yosemite is where the first nest south of Canada was found in 1914. A study of the Yosemite owls shows that this population has been genetically isolated from populations in Oregon and farther north for more than 25,000 years. Biologists working on that study suggest that the Yosemite population should be considered a separate sub-species (Strix nebulosa yosemitensis). [8] Nearby populations at lower elevations were not tested.
In Washington state, great grey owls are found in the southeast where mountains extend up from Oregon and in the Colville National Forest. Only a handful of great grey owl nests have ever been found in Washington state.
Farther east in the western United States, great grey owls breed in Idaho, Montana, and Wyoming, as far south as the Grand Teton and Yellowstone National Parks.
In northeastern North America, the owls are found year-round in southern Quebec and Ontario, but individuals will sometimes move further south in winter into New York and New England, apparently in pursuit of more abundant prey. [9] Great grey owls are rarely sighted as far south as Pennsylvania and Long Island, New York. [9] In winter 2017, the birds were recorded in northern New York in Robert Moses State Park and central Maine. [10]
Great grey owls do not build nests, so they typically use nests previously used by a large bird, such as a raptor. They will also nest in broken-topped trees and cavities in large trees. In southwestern and northeastern Oregon, the great grey owl has been using man-made platforms for nest sites since the 1980s. The erection of nest platforms for great grey owls was pioneered by Robert Nero in central Canada in the 1970s. Nesting may occur from March to May. Unlike, for example, osprey or white storks, the great grey owl does not predictably re-use nest sites over consecutive years. Four eggs are the usual clutch size. Eggs average 42.7 mm (1.68 in) wide and 53.5 mm (2.11 in) long. The incubation period is about 30 days, ranging from 28 to 36 days. Brooding lasts 2 to 3 weeks, after which the female starts roosting on a tree near nests. The young jump or fall from the nest at 3 to 4 weeks, and start to fly 1 to 2 weeks after this. Immediately after fledging, the white, fuzzy young must use beak and feet to climb back into trees. The female is on guard at this time and may be aggressive toward potential predators. Most offspring remain near their natal sites for many months after fledging. Normally the male hunts for his mate and the young throughout the nesting period. Once the young begin the fly, the female typically withdraws and the male continues to feed the young until they can hunt on their own in the autumn. The young owls go off on their own by winter.
The abundance of food in the area usually affects the number of eggs a female lays, a feature quite common in northern owl species. In years when small mammal populations are very low the great grey owl may not attempt nesting; thus their reproduction is connected to the sometimes extreme fluctuations of small mammal populations. Also, great grey owls may not nest in years of drought. If food is scarce, they may travel a fair distance to find more prey, with considerable movements by large numbers in some years of particularly scarce prey. Though they do not migrate, many are at least somewhat nomadic.
One alert landowner in northeast Oregon, Andy Huber, helped a female great grey owl raise her four nestlings after a great horned owl killed the male. Huber live-trapped small mammals and then released them at the nest site, and the female took these to the nestlings. As the owlets matured and began flying they came for the prey on their own. Huber and the mother owl raised all four owlets successfully. [11]
These birds wait, listen, and watch for prey, then swoop down; they also may fly low through open areas in search of prey. They frequently hunt from a low listening post which can be a stump, low tree limb, fence post, or road sign. Their large facial discs, also known as "ruffs", focus sound, and the asymmetrical placement of their ears assists them in locating prey, because of the lack of light during the late and early hours in which they hunt. On the nesting grounds, they mainly hunt at night and near dawn and dusk; at other times, they are active mostly during the night.
They have excellent hearing, and may locate (and then capture) prey moving beneath 60 cm (2.0 ft) of snow in a series of tunnels solely with that sense. They then can crash to a snow depth roughly equal to their own body size to grab their prey. Only 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. [12]
Unlike the more versatile eagle and horned owls, great grey owls rely almost fully upon small rodents. What species they eat depends on which small mammals are most abundant and available. In northern Canada and other parts of Scandinavia, they eat lemmings primarily. In dry parts of California's Sierra Nevada they eat mostly pocket gophers. In some areas voles are the predominant prey. Locally, alternative prey animals (usually comprising less than 20% of prey intake) include squirrels, hares, moles, shrews, weasels, thrushes, grouse, Canada jays, mountain quail, small hawks, ducks, frogs and large beetles. [13] This species is not known to 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.
The harvest of timber from the great grey owl's habitat is, perhaps, the greatest threat to this species. [14] Intensified timber management typically reduces live and dead large-diameter trees used for nesting, leaning trees used by juveniles for roosting before they can fly, and dense canopy closures in stands used by juveniles for cover and protection. [14] If perches are not left in clearcuts, great grey owls cannot readily hunt in them. Although human-made structures (made specifically for use by this species) have been utilized by these owls, the species is far more common in areas protected from logging. Livestock grazing in meadows also adversely affects great grey owls, by reducing habitat for preferred prey species. [14]
Other dangers to great grey owls include rodenticides, collisions with vehicles, and the West Nile Virus. The West Nile virus is likely to become more prevalent with climate change. In Ontario and northeastern Oregon there are confirmed great grey owl deaths from the virus. Testing of owls in the Yosemite area since 2005 has found evidence of the virus in that population.
Due to their large size, great grey owls have few natural predators. Great horned owls, various small carnivores, and black bears have been documented preying on young, but such predators rarely threaten adults, and owls have been known to fend off animals as large as black bears when defending their nests. [15] The only known predator of adult great grey owls is the Eurasian eagle-owl (Bubo bubo), which occasionally preys on the former in parts of Europe. [16]
The great grey owl is not as aggressive as most other apex predators. They are less likely to attack each other or potential threats than are other large predatory birds. They do not protect a large nesting territory, nor do they defend hunting territories through aggression. As an exception, the female is aggressive in protecting eggs and owlets. She is especially alert and aggressive when fledglings first leave the nest but cannot yet fly, and thus are extremely vulnerable.
This lack of territorial aggressiveness makes the great grey owl difficult to find in the field. Most owls respond to their own species calls if played back in a nesting territory. Great grey owls will often ignore such calls. They also do not flush every time a human approaches or drives past. The great grey owl often remains still even if a human is nearby and therefore they are often overlooked or unnoticed.
The great grey owl is the provincial bird of Manitoba, Canada.
As of 2016, there are four great grey owls captive in Oregon and California. Two live at Blue Mountain Wildlife near Pendleton, Oregon, a third lives at Lindsay Museum in Walnut Creek, California, [17] and the fourth lives at CuriOdyssey in San Mateo, California. [18]
A captive wild injured great grey owl, Boris, resides at the Alaska Raptor Center in Sitka, Alaska. Boris was found north of Anchorage with a trauma to his right wrist, leaving him flightless. [19]
Another captive wild injured great grey owl, Errol, lives at the Alaska Zoo in Anchorage, Alaska. Errol came to the zoo from Wild Bird Rescue after injuring himself while colliding with the tire of a parked car. [20]
The Eurasian subspecies of the grey owl is very commonly kept in European zoos.
A great grey owl with human hands is depicted on William Schaff's album art for The Magnolia Electric Co. , a 2003 alt-country album by Songs: Ohia. [21]
The bald eagle is a bird of prey found in North America. A sea eagle, it has two known subspecies and forms a species pair with the white-tailed eagle, which occupies the same niche as the bald eagle in the Palearctic. Its range includes most of Canada and Alaska, all of the contiguous United States, and northern Mexico. It is found near large bodies of open water with an abundant food supply and old-growth trees for nesting.
The great blue heron is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North and Central America, as well as far northwestern South America, the Caribbean and the Galápagos Islands. It is occasionally found in the Azores and is a rare vagrant to Europe. An all-white population found in south Florida and the Florida Keys is known as the great white heron. Debate exists about whether these white birds are a color morph of the great blue heron, a subspecies of it, or an entirely separate species.
The northern harrier, also known as the marsh hawk or ring-tailed hawk, is a bird of prey. It breeds throughout the northern parts of the northern hemisphere in Canada and the northernmost USA.
The snowy owl, 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 that 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 to age and sex individual snowy owls.
The long-eared owl, also known as the northern long-eared owl or, more informally, as the lesser horned owl or cat owl, is a medium-sized species of owl with an extensive breeding range. The genus name, Asio, is Latin for "horned owl", and the specific epithet, otus, is derived from Greek and refers to a small eared owl. The species breeds in many areas through Europe and the Palearctic, as well as in North America. This species is a part of the larger grouping of owls known as typical owls, of the family Strigidae, which contains most extant species of owl.
The northern hawk-owl or northern hawk owl is a medium-sized true owl of the northern latitudes. It is non-migratory and usually stays within its breeding range, though it sometimes irrupts southward. It is one of the few owls that is neither nocturnal nor crepuscular, being active only during the day. This is the only living species in the genus Surnia of the family Strigidae, the "typical" owls. The species is sometimes called simply the hawk owl; however, many species of owls in the genus Ninox are also called "hawk owls".
The great horned owl, also known as the tiger owl or the hoot owl, is a large owl native to the Americas. It is an extremely adaptable bird with a vast range and is the most widely distributed true owl in the Americas. Its primary diet is rabbits and hares, rats and mice, and voles, although it freely hunts any animal it can overtake, including rodents and other small mammals, larger mid-sized mammals, birds, reptiles, amphibians, and invertebrates.
The barred owl, also known as the northern barred owl, striped owl or, more informally, hoot owl or eight-hooter owl, is a North American large species of owl. A member of the true owl family, Strigidae, they belong to the genus Strix, which is also the origin of the family's name under Linnaean taxonomy. Barred owls are largely native to eastern North America, but have expanded their range to the west coast of North America where they are considered invasive. Mature forests are their preferred habitat, but they can also acclimatise to various gradients of open woodlands. Their diet consists mainly of small mammals, but this species is an opportunistic predator and is known to prey upon other small vertebrates such as birds, reptiles, and amphibians, as well as a variety of invertebrates.
The eastern screech owl or eastern screech-owl, is a small owl that is relatively common in Eastern North America, from Mexico to Canada. This species resides in most types of woodland habitats across its range, and is relatively adaptable to urban and developed areas compared to other owls. Although it often lives in close proximity to humans, the eastern screech owl frequently avoids detection due to its strictly nocturnal habits.
The Canada jay, also known as the grey jay, gray jay, camp robber, or whisky jack, is a passerine bird of the family Corvidae. It is found in boreal forests of North America north to the tree line, and in the Rocky Mountains subalpine zone south to New Mexico and Arizona. A fairly large songbird, the Canada jay has pale grey underparts, darker grey upperparts, and a grey-white head with a darker grey nape. It is one of three members of the genus Perisoreus, a genus more closely related to the magpie genus Cyanopica than to other birds known as jays. The Canada jay itself has nine recognized subspecies.
Cooper's hawk is a medium-sized hawk native to the North American continent and found from southern Canada to Mexico. This species was formerly placed in the genus Accipiter. As in many birds of prey, the male is smaller than the female. The birds found east of the Mississippi River tend to be larger on average than the birds found to the west. It is easily confused with the smaller but similar sharp-shinned hawk.
The red-tailed hawk is a bird of prey that breeds throughout most of North America, from the interior of Alaska and northern Canada to as far south as Panama and the West Indies. It is one of the most common members within the genus of Buteo in North America or worldwide. The red-tailed hawk is one of three species colloquially known in the United States as the "chickenhawk", though it rarely preys on standard-sized chickens. The bird is sometimes also referred to as the red-tail for short, when the meaning is clear in context.
The boreal owl or Tengmalm's owl is a small owl in the "true owl" family Strigidae. It is known as the boreal owl in North America and as Tengmalm's owl in Europe after Swedish naturalist Peter Gustaf Tengmalm or, more rarely, Richardson's owl after Sir John Richardson.
The spotted owl is a species of true owl. It is a resident species of old-growth forests in western North America, where it nests in tree hollows, old bird of prey nests, or rock crevices. Nests can be between 12 and 60 metres high and usually contain two eggs. It is a nocturnal owl which feeds on small mammals and birds. Three subspecies are recognized, ranging in distribution from British Columbia to Mexico. The spotted owl is under pressure from habitat destruction throughout its range, and is currently classified as a near-threatened species.
The Ural owl is a large nocturnal owl. It is a member of the true owl family, Strigidae. The Ural owl is a member of the genus Strix, that is also the origin of the family's name under Linnaean taxonomy. Both its common name and scientific name refer to the Ural Mountains of Russia where the type specimen was collected. However, this species has an extremely broad distribution that extends as far west as much of Scandinavia, montane eastern Europe, and, sporadically, central Europe, thence sweeping across the Palearctic broadly through Russia to as far east as Sakhalin and throughout Japan. The Ural owl may include up to 15 subspecies, but most likely the number may be slightly fewer if accounting for clinal variations.
The powerful owl, a species of owl native to south-eastern and eastern Australia, is the largest owl on the continent. It is found in coastal areas and in the Great Dividing Range, rarely more than 200 km (120 mi) inland. The IUCN Red List of Threatened Species also refers to this species as the powerful boobook.
The tawny owl, also called the brown owl, is a stocky, medium-sized owl in the family Strigidae. It is commonly found in woodlands across Europe, as well as western Siberia, and has seven recognized subspecies. The tawny owl's underparts are pale with dark streaks, whilst its upper body may be either brown or grey. The tawny owl typically makes its nest in a tree hole where it can protect its eggs and young against potential predators. It is non-migratory and highly territorial: as a result, when young birds grow up and leave the parental nest, if they cannot find a vacant territory to claim as their own, they will often starve.
The golden eagle is one of the most powerful predators in the avian world. One author described it as "the pre-eminent diurnal predator of medium-sized birds and mammals in open country throughout the Northern Hemisphere". Golden eagles usually hunt during daylight hours, but were recorded hunting from one hour before sunrise to one hour after sunset during the breeding season in southwestern Idaho. The hunting success rate of golden eagles was calculated in Idaho, showing that, out of 115 hunting attempts, 20% were successful in procuring prey. A fully-grown golden eagle requires about 230 to 250 g of food per day. In the life of most eagles, there are cycles of feast and famine, and eagles have been known to go without food for up to a week. Following these periods without food, they will then gorge on up to 900 g (2.0 lb) at one sitting. The powerful talons of the golden eagle ensure that few preys can escape them once contact is made. The talons of this species exert approximately 440 pounds per square inch (3 MPa) of pressure, around 15 times more pressure than is exerted by the human hand, although some claim that the largest individual females may reach a pressure of 750 psi (5.2 MPa). It has been claimed that the golden eagle can lift more than its own body weight in flight. However, other sources claim that a hare, marmot or deer calf weighing 4 kg (8.8 lb) is a struggle for even a large female to carry and that prey much over 2 kg (4.4 lb) would require favorably high wind conditions.
The Eurasian goshawk is a species of medium-large bird of prey in the family Accipitridae, a family which also includes other extant diurnal raptors, such as eagles, buzzards and harriers. It was formerly placed in the genus Accipiter. It is a widespread species that inhabits many of the temperate parts of the Eurasia. Except in a small portion of southern Asia, it is the only species of "goshawk" in its range and it is thus often referred to, both officially and unofficially, as simply goshawk. It is mainly resident, but birds from colder regions migrate south for the winter. As of 2023, goshawks found in North America are no longer considered be conspecific, but are now designated as the American goshawk.
The red-shouldered hawk is a medium-sized buteo. Its breeding range spans eastern North America and along the coast of California and northern to northeastern-central Mexico. It is a permanent resident throughout most of its range, though northern birds do migrate, mostly to central Mexico. The main conservation threat to the widespread species is deforestation.
The great grey owl (GGO) was placed on the California state endangered species list in June 1980.
For Belarus, Finland, Georgia, Ukraine, United States, with world range map.
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