Northern Hawk Owl
Encyclopedia
The Northern Hawk-Owl is a non-migratory owl that usually stays within its breeding range. It sometimes irrupts southward.

General

It is the only living species in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Surnia. The species is sometimes called simply the Hawk Owl; however, many species of owls in the Ninox
Ninox
Ninox is a genus of owls comprising about 20 species found in Asia and Australasia. Many species are known as hawk owls or boobooks...

genus are also called hawk owls.

Description

The Northern Hawk-Owl (Surnia ulula) also known as the Hawk-Owl is an owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...

 from the family (Strigidae) which resides within the circumpolar
Circumpolar
The term circumpolar may refer to:* circumpolar navigation: to travel the world "vertically" traversing both of the poles* Antarctic region** Antarctic Circle** the Antarctic Circumpolar Current** Subantarctic** List of Antarctic and subantarctic islands...

 regions in the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

. Male Northern Hawk-Owls are generally 36.0–42.5 cm long and weigh 300 g. Females are slightly bigger with a length of 37.2–44.7 cm and a mass of about 340g. Both male and female have similar wingspans of about 45 cm. The Northern Hawk-Owl plumage is relatively dark brown with an off white spotting pattern on all dorsal parts of the body with the exception of the back of the neck which boasts a black v-shaped pattern. The underbelly is generally white or off-white which continues to the toes with brown bands on the breast and stomach. It also boasts a long tail with brown banding. The Northern Hawk-Owl has a smokey white face with a black border, a flat head, yellow eyes and a yellow curved beak.

The Northern Hawk-Owl has been said to resemble a hawk in appearance and in behavior. More precisely it is said to look like the Cooper ’s Hawk (Accipiter cooperii). It has been suggested that this may be because the Hawk-Owl may partially fill an important diurnal
Diurnal cycle
A diurnal cycle is any pattern that recurs every 24 hours as a result of one full rotation of the Earth.In climatology, the diurnal cycle is one of the most basic forms of climate patterns. The most familiar such pattern is the diurnal temperature variation...

 niche similar to that of day hunters such as hawks.

Vocalization

S. ulula has a variety of calls used by the different sexes in different situations. When attracting a mate the male usually lets out a rolled whistle of ulululululululul and a sound similar to tu-wita-wit, tiwita-tu-wita, wita, when perch
Perch (equilibristic)
The perch is an equilibristic balancing act where one performer balances atop a pole that is being balanced by another performer. Each perch pole has a loop at the top into which the performer may insert either a hand or a foot in order to perform a variety of tricks while hanging down from the loop...

ing at a potential nest site. The female’s call is usually less constant and more shrill.

When alerting to danger, the Northern Hawk-Owl lets out a sound similar to rike, rike, rike, rike. It also releases a high pitched scream followed by a yip when an intruder is near to the nest. To warn of impending dangers to a fledgling, the Hawk-Owl will let out a noise similar to ki ki kikikikiki. Calls can vary in length from 15 s to 2 min.

Breeding

The Northern Hawk-Owl generally starts its mating rituals at the beginning of March. After calling and pairing is complete the Northern Hawk-Owl will build a nest and start to lay eggs. On average the Northern Hawk-Owl will lay 3-11 eggs per brood. The nest sites are usually the tops of hollow stumps of old dead spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...

 trees. These nesting sites are usually 2-10m above ground for the North American
North American
North American generally refers to an entity, people, group, or attribute of North America, especially of the United States and Canada together.-Culture:*North American English, a collective term used to describe American English and Canadian English...

 S. u. caparoch and approximately 4-5m above ground for the Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

n S. u. ulala. The specific dates of egg appearance can be quite variable depending on locality. In central Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 eggs are usually laid from March 30 to the 5th of June. In Newfoundland
Newfoundland and Labrador
Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...

 the appearance eggs occurs later, between May 9 and June 11. In Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

 however, eggs can be found anywhere between the 30th of March to the 23rd of June.

For the most part the female Northern Hawk-Owl does the incubating of the eggs whilst the male forages for food. Once the chicks have hatched their roles shift drastically. At about two weeks into the chicks lives the female starts to leave the nest for long spans of time (5 hours or more). This span of time is presumably when the female hunts. The male however, will guard the nest diligently until the chicks leave. When predators (usually other raptors
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....

) fly nearby, the male will sometimes chase them away from the nest if they feel it is necessary. Once the owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...

ets have grown to a size which allows less parental supervision, they will leave the nest. This occurs on average after their 21st day, and can begin as early as mid-June. After this the female will provide most of the care. However the male will remain close and will still feed his young on occasion.
The Northern Hawk-Owl has also been known to nest on cliffsides. It has little fear of humans, and will attack if the young are approached too closely.

Habitat and Distribution

The Northern Hawk-Owl is distributed throughout the boreal forests of the world. In North America, the Northern Hawk-Owl can be seen as far north as the Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

n tree line and the northern Canadian territories. Occasionally, the Hawk-Owl can extend its territory as far south as northern Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

 and many other states in the northern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 including more central states such as West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...

, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, and South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

. These southern forays into the northern United States are rare and generally occur during winter, or following an explosion in a population of prey. The normal distribution however, tends to be throughout Canada from the Alaskan coast to the northern portion of Newfoundland.

In Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

, again the Northern Hawk-Owl’s range is throughout the boreal forest, usually found in northern Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...

, northern Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 to central Russia and northern Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...

 . As in North America the Northern Hawk-Owl can occasionally be found in more southern areas such as the following: Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

; and southern Russia and Scandinavia, following explosions of prey.

Feeding

The Northern Hawk-Owl feeds on a variety of prey which can include small rodents to mammals more robust in size and a variety of birds, a typical diet for many boreal owls. In Eurasia the Northern Hawk-Owl is known to feed primarily on voles from the Microtus
Microtus
The genus Microtus is a group of voles found in North America, Europe and northern Asia. The genus name refers to the small ears of these animals. There are 62 species in the genus....

 family. These voles usually follow a 3-4 year cycle of abundance. Therefore, S. u. ulula numbers are affected negatively when the numbers of voles are lowest. In North America the subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 S. u. caparoch also feeds upon microtine
Microtus
The genus Microtus is a group of voles found in North America, Europe and northern Asia. The genus name refers to the small ears of these animals. There are 62 species in the genus....

 voles, but its population is primarily based on the ten year cycling of the Snowshoe Hare
Snowshoe Hare
The Snowshoe Hare , also called the Varying Hare, or Snowshoe Rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet and the marks its tail leaves. The animal's feet prevent it from sinking into the snow when it hops and walks...

 (Lepus americanus). In Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

 the Northern Hawk-Owl’s body mass consists of about 94 % microtine voles, whereas in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 the percentage of biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 contributed by voles can be as low as 20 %. Juvenile hares are considerably more important at 40-50%.

Other animals which are important prey items for the Northern Hawk-Owl include the red squirrel
Red Squirrel
The red squirrel or Eurasian red squirrel is a species of tree squirrel in the genus Sciurus common throughout Eurasia...

 (taniasciurus handsonicus) which has been documented contributing 20% to the Hawk-Owl’s biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

. A long list of others include mice
MICE
-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...

, rats
RATS
RATS may refer to:* RATS , Regression Analysis of Time Series, a statistical package* Rough Auditing Tool for Security, a computer program...

, voles, lemming
Lemming
Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae , which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats,...

s, the short-tail weasel (Mustela erminea), partridge
Partridge
Partridges are birds in the pheasant family, Phasianidae. They are a non-migratory Old World group.These are medium-sized birds, intermediate between the larger pheasants and the smaller quails. Partridges are native to Europe, Asia, Africa, and the Middle East...

, Spruce Grouse
Spruce Grouse
The Spruce Grouse or Canada Grouse is a medium-sized grouse closely associated with the coniferous boreal forests or taiga of North America. It is one of the most arboreal grouse, fairly well adapted to perching and moving about in trees...

 (Falcipennis canadensis), doves
Doves
Doves are an English alternative indie rock band, originating from Wilmslow, Cheshire. The band comprises brothers Jez Williams and Andy Williams , and Jimi Goodwin . The members started working seriously together after meeting at The Haçienda in Manchester. Doves' unofficial fourth member is...

, Pileated Woodpeckers (Dryocopus pileatus), sparrows, jays, robin
European Robin
The European Robin , most commonly known in Anglophone Europe simply as the Robin, is a small insectivorous passerine bird that was formerly classed as a member of the thrush family , but is now considered to be an Old World flycatcher...

s, starlings, buntings, grackles, and finches. In the winter feeding strategies change, where in summer the main source of food is mammals, in the winter a bigger portion of the Hawk-Owl’s biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 consists of ground dwelling birds such as the ptarmigan and the grouse
Grouse
Grouse are a group of birds from the order Galliformes. They are sometimes considered a family Tetraonidae, though the American Ornithologists' Union and many others include grouse as a subfamily Tetraoninae in the family Phasianidae...

.

The Northern Hawk-Owl, is a partially diurnal hunter although it has been recorded hunting at varying times and does not appear to have a preferred hunting time. Whether the bird resides in Eurasia or North America, the strategy is usually similar. The Northern Hawk-Owl will perch and scower the immediate area for prey. As theseowl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...

s are considered a search orientated species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 they likely do not stay put for long if the site is not producing prey. The Hawk-Owl prefers open forest type environments when perching. These environments include sphagnum
Sphagnum
Sphagnum is a genus of between 151 and 350 species of mosses commonly called peat moss, due to its prevalence in peat bogs and mires. A distinction is made between sphagnum moss, the live moss growing on top of a peat bog on one hand, and sphagnum peat moss or sphagnum peat on the other, the...

 bogs and partially deforested areas. The preferred perching tree of the Northern Hawk-Owl is the spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...

 tree. When the Hawk-Owl attacks, it goes from a horizontal posture into a gliding dive. If the prey is further away the bird will flap its wings a few times during the dive to increase distance. The Hawk Owl has exceptional hearing and can plunge into snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

 to capture rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

s below the surface.

The type of prey the Hawk-Owl catches will determine its eating strategy. For mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

ian prey the ritual is generally the same, the Northern Hawk-Owl will eviscerate
Disembowelment
Disembowelment is the removal of some or all of the organs of the gastrointestinal tract , usually through a horizontal incision made across the abdominal area. Disembowelment may result from an accident, but has also been used as a method of torture and execution...

 its prey, eat the head first especially for prey like the red squirrel
Red Squirrel
The red squirrel or Eurasian red squirrel is a species of tree squirrel in the genus Sciurus common throughout Eurasia...

 whose head is fairly large, and then it will either eat the organs and cache
Cache
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...

 the remains for bigger prey, organisms or swallow the body whole for smaller prey animals.

Taxonomy

The genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Surnia contains only one species, the Northern Hawk-Owl (Surnia ulala). However, there are three recognized subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

. The North American variety of Northern Hawk-Owl S. u. caparoch has been known to reach Great Britain at times but generally resides in Canada and Alaska. In Eurasia there exists two sub-species. One variety, S. u. tianschanica, breed
Breed
A breed is a group of domestic animals or plants with a homogeneous appearance, behavior, and other characteristics that distinguish it from other animals or plants of the same species. Despite the centrality of the idea of "breeds" to animal husbandry, there is no scientifically accepted...

s in central Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 reaching Xinjiang
Xinjiang
Xinjiang is an autonomous region of the People's Republic of China. It is the largest Chinese administrative division and spans over 1.6 million km2...

  (China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

). The other variety, S. u. ulula, resides across Eurasia reaching Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

 at its most eastern range.

The Northern Hawk-Owl is in the family Strigidae, but there is no known fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 evidence of others in its genus. There have been genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 tests done however, which relate the S. ulula to other species such as the Spotted Owlet
Spotted Owlet
The Spotted Owlet is a small owl which breeds in tropical Asia from India to Southeast Asia. A common resident of open habitats including farmland and human habitation, it has adapted to living in cities. They roost in small groups in the hollows of trees or in cavities in rocks or buildings. It...

 (Athena brama) and the Little Owl
Little Owl
The Little Owl is a bird which is resident in much of the temperate and warmer parts of Europe, Asia east to Korea, and north Africa. It is not native to Great Britain, but was first introduced in 1842, and is now naturalised there...

(A. noctua).

External links

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