great horned owl

Great Horned Owl
Coastal Great Horned Owl, B. v. saturatus Reifel Migratory Bird Sanctuary, Delta, British Columbia (Canada)
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Strigiformes
Family:	Strigidae
Genus:	Bubo
Species:	B. virginianus
Subspecies
About one dozen, see text
Synonyms
Strix virginiana Gmelin, 1788 and see text

The Great Horned Owl, Bubo virginianus, is a large owl native to the Americas. It is an adaptable bird with a vast range and is the most widely distributed true owl in the Americas.

The Magellanic Horned Owl (B. magellanicus) of the Pacific Andes was for some time included in this species too.

Description

Individual Great Horned Owls range in length from 18-27 in (46-68 cm) and have a wingspan of 40-60.5 in (101-153 cm); Females are larger than males, an average adult being 22 in (55 cm) long with a 49 in (124 cm) wingspan and weighing about 3.1 lbs (1400 g). Bergmann's Rule generally holds: larger individuals are found towards Polar regions, smaller towards the Equator.

Face of a Common Great Horned Owl (B. v. virginianus) in North Carolina

Adults have large ear tufts, a reddish, brown or gray face and a white patch on the throat. The iris is yellow, except the amber-eyed South American Great Horned Owl (B. v. nacurutu). Its "horns" are neither ears nor horns, simply tufts of feathers. The underparts are light with brown barring; the upper parts are mottled brown. The legs and feet are covered in feathers up to the talons. There are individual and regional variations in color; birds from the sub-Arctic are a washed-out, light-buff color, while those from Central America can be a dark chocolate brown.

Their call is a low-pitched but loud ho-ho-hoo hoo hoo; sometimes it is only four syllables instead of five. The female's call is higher and rises in pitch at the end of the call. Young owls make hissing or screeching sounds that are often confused with the calls of Barn Owls.

Great Horned Owls can be easily confused with the Magellanic Horned Owl (B. magellanicus) and other eagle-owls. They are all generally allopatric though.

Subspecies

A large number of subspecies have been named. As indicated above, many of these are only examples of individual or clinal variation. Subspecies differences are mainly in color and size and generally follow Gloger's and Bergmann's Rules:^[1]

• Common Great Horned Owl, B. v. virginianus (Gmelin, 1788) – USA eastwards from Minnesota to E Texas; northeastwards to Nova Scotia and Prince Edward Island, Canada. Resident all-year.

A brown form, tinged rufous and barred distinctly blackish-brown below. Feet tawny to buff, often barred black.

South American Great Horned Owl, B. v. nacurutu (note dark eyes)

Californian Great Horned Owl (B. v. pacificus) stretching itself, Bernal Hill Park, San Francisco

• South American Great Horned Owl, B. v. nacurutu (Vieillot, 1817) – A lowland form occurring in disjunct populations from from E Colombia to the Guyanas; also from Bolivia and Brazil south of the Amazonas basin to N Argentina; resident all-year. Includes the proposed subspecies scotinus, elutus, and deserti^[2]. The status of this form, especially the relationships between the subpopulations and with ssp. nigrescens and the Magellanic Horned Owl, deserves more study.

Dull brownish with long bill; birds from the semiarid interior of Brazil often have much white on uppertail- and ear-coverts. It is the only subspecies where the iris is amber, not yellow.

• Northern Great Horned Owl, B. v. subarcticus Hoy, 1852 – Breeding range from Mackenzie, British Columbia region E to Hudson Bay; southern limit unclear but at least reaches to Montana and North Dakota. Non-breeding birds are regularly found south to latitude 45°S, occasionally beyond. Includes the birds described as occidentalis (but see below), and sclariventris^[3]. The older name wapacuthu was occasionally used for this subspecies, but it cannot with certainty be assigned to a recognizable taxon and is thus considered a nomen dubium. The population described as algistus is probably based on wandering individuals and/or intergrades of subarcticus, saturatus and lagophonus.^[2]

A pale form, essentially whitish with faint buff tinge above; black underside barring variable from indistinct to pronounced. Very pale birds are similar to a young female Snowy Owl from a distance. Feet whitish to buff, with little or no pattern.

• Californian Great Horned Owl, B. v. pacificus Cassin, 1854 – Central and southern California west of the Sierra Nevada except San Joaquin Valley, south to NW Baja California, Mexico. Intergrades with pallescens in San Diego County, California (see also below). Resident all-year.

Very rich brown, dark underside barring distinct but less pronounced than in saturatus. Humeral area black. Feet mottled dark.

• Coastal Great Horned Owl, B. v. saturatus Ridgway, 1877 – Pacific coast from SE Alaska to N California. Resident all-year.

A dark, dull and somewhat greyish form with heavily barred underside. Feet fairly dusky overall.

• North Andean Great Horned Owl, B. v. nigrescens Berlepsch, 1884 – Andes; arid temperate and puna zones from Colombia to NW Peru. Resident all-year round.

A dark, cold gray-brown form with heavy fuscous blotching.

• Desert Great Horned Owl, B. v. pallescens Stone, 1897 – San Joaquin Valley southeastwards through arid regions of SE California and S Utah eastwards to W Kansas and southwards to Guerrero and W Veracruz in Mexico; intergrades with pacificus in San Diego County; vagrant individuals of lagophonus and the Rocky Mountains population, which look similar to intergrades, also seem to occur in its range. Resident all-year.

A small, pale dusky buff form with indistinct barring, especially on the underside. Humeral area umber. Feet white and usually unmarked.

• Yucatán Great Horned Owl, B. v. mayensis (Nelson, 1901) – Yucatán Peninsula. Resident all-year.

A small and medium pale form.

• Baja California Great Horned Owl, B. v. elachistus Brewster, 1902 – S Baja California, Mexico. Resident all-year.

Similar in color to pacificus, but considerably (5-10%) smaller; some overlap though.

• Northeastern Great Horned Owl, B. v. heterocnemis (Oberholser, 1904) – Breeds in E Canada (N Quebec, Labrador, Newfoundland). In winter, disperses southwards to Ontario to NE USA. Doubtfully distinct from saturatus^{[verification needed][2]}.

A fairly dark and grey, heavily barred form. Feet pale with dusky mottling.

• Northwestern Great Horned Owl, B. v. lagophonus (Oberholser, 1904) – Breeds from inland Alaska south through mountaineous areas of British Columbia to MA Oregon, the Snake River, and NW Montana. Reported in winter as far south as Colorado and Texas. Doubtfully distinct from saturatus^[2].

Greyer than saturatus, but similar overall. Feet with dusky barring.

• Central American Great Horned Owl, B. v. mesembrinus (Oberholser, 1904) – Isthmus of Tehuantepec to W Panama. Resident all-year.

A mid-sized form; darker than mayensis.

• Rocky Mountains Great Horned Owl, B. v. ssp. nov.? – The Rocky Mountains population may constitute an as yet undescribed subspecies. It breeds south of the Snake River south to Arizona, New Mexico, and the Guadalupe Mountains. Westwards, it is presumed to occur to the Modoc Plateau and Mono Lake. The name occidentalis may apply to these birds pending analysis of the type specimen; certainly, they were included in the presumed subspecies named thus, but intergradation between pallescens and lagophonus and altitudinal migration of Rocky Mountain birds is not sufficiently researched yet^[2].

A medium gray form, intermediate between lagophonus and pallescens. Moderately barred and tinged buff on the underside. Feet mottled.

The Pleistocene Sinclair Owl from California, Bubo sinclairi, may have been be a paleosubspecies of this species.^[4]

Distribution and ecology

Video of a Great Horned Owl at Disney's Animal Kingdom

The breeding habitat of the Great Horned Owl extends from subarctic North America through much of Central America and South America south to Tierra del Fuego. They are absent from southern Guatemala, El Salvador and Nicaragua to Panama in Central, and Amazonia and the southwest in South America, as well as from the West Indies and indeed most off-shore islands.^[5]

Within their habitat they can take up residence in trees that include deciduous, coniferous, and mixed forests, tropical rainforests, pampas, prairie, mountainous areas, deserts, subarctic tundra, rocky coasts, mangrove swamp forests, and some urban areas. It is less common in the more extreme areas (i.e. the heart of the deserts, extremely dense rainforests and in mountainous regions), generally absent from non-tidal wetland habitat^[6], and missing from the high Arctic tundra. All mated Great Horned Owls are permanent residents of their territories, but unmated and younger birds move freely in search of company and a territory, and leave regions with little food in winter.

Great Horned Owl eggs, nestlings and fledgings may be preyed on by foxes, coyotes, or wild or feral cats. There are almost no predators of adults, but they may be killed in confrontations with eagles, Snowy Owls and, mostly, other Great Horned Owls. Far-ranging as it is, it is not considered a globally threatened species by the IUCN^[7]

Food and feeding behavior

Composite photo of Great Horned Owl flight phases

Owls have spectacular binocular vision allowing them to pinpoint prey and see in low light. The eyes of Great Horned Owls are nearly as large as those of humans and are immobile within their circular bone sockets. Instead of turning their eyes, they turn their heads. Therefore, their neck must be able to turn a full 270 degrees in order to see in other directions without moving its entire body.

An owl's hearing is as good – if not better – than its vision; they have better depth perception^{[citation needed]} and better perception of sound elevation (up-down direction) than humans. This is due to owl ears not being placed in the same position on either side of their head: the right ear is typically set higher in the skull and at a slightly different angle. By tilting or turning its head until the sound is the same in each ear, an owl can pinpoint both the horizontal and vertical direction of a sound.

Closeup of a Great Horned Owl toe and talon

These birds hunt at night by waiting on a high perch and swooping down on prey. Prey is varied. Predominantly small to medium-sized mammals such as hares, rabbits, racoons, rats, squirrels, mice, moles, voles, marmots, shrews, bats, armadillos, weasels and gerbils. It's even a natural predator of porcupines and skunks (like most birds it has poor sense of smell). Birds also comprise a large portion of a Great Horned Owl's diet, ranging in size from kinglets to Great Blue Herons. Waterbirds, especially coots and ducks, are hunted; even raptors, up to the size of Snowy Owls, are sometimes taken. The owls sometimes eat farmers' chickens and small to medium and largish dogs^{[citation needed]}. But reptiles, amphibians, fish, crustaceans and even insects only count for occasional prey. Cannibalism has been recorded.

These birds also have 500 pounds per square inch of crushing power in their talons. An average adult human male has about 60 pounds per square inch in his hands.^{[citation needed]} In northern regions, where larger prey that cannot be eaten quickly are most prevalent, they may let uneaten food freeze and then thaw it out later using their own body heat. They also tend to eat and regurgitate food in the same locations.

Reproduction

Nestlings of the enigmatic Rocky Mountains population in New Mexico

Great Horned Owls are some of the earliest-breeding birds in North America. They breed in late January or early February and are often heard calling to each other in the fall, starting in October. They choose a mate by December and are often heard duetting before this time. For owls found in more tropical climates, the dates of the breeding season are somewhat undefined. They often take over a nest used by some other large bird, sometimes adding feathers to line the nest but usually not much more. Old crow and raven (Corvus), Red-tailed Hawk (Buteo jamaicensis) or large squirrel nests are often favored in North America. However, they are far from dependent on the old nests of others and may use cavities in trees and snags, cliffs, deserted buildings, and artificial platforms.

There are usually 2 eggs per clutch, with a clutch ranging in size from 1 to 5 eggs (5 is very rare). The average egg width is 1.8 in (46.5 mm), the average length is 2.2 in (55.2 mm) and the average weight is 1.8 oz (51 g). The incubation period ranges from 30 to 37 days, averaging 33 days. Brooding is almost continuous until the offspring are about 2 weeks old, after which it decreases. Young owls move onto nearby branches at 6 weeks and start to fly about a week later. The offspring have still been seen begging for food in late October (5 months after leaving the nest) and most do not separate from their parents until right before they start to reproduce for the next clutch (usually December). Birds may not breed for another year or two, and are often vagrants ("floaters") until they mate, establish their own territories, and settle down.

Provincial Bird

The Great Horned Owl is the provincial bird of Alberta.

Footnotes

References

• Accordi, Iury Almeida & Barcellos, André (2006): Composição da avifauna em oito áreas úmidas da Bacia Hidrográfica do Lago Guaíba, Rio Grande do Sul [Bird composition and conservation in eight wetlands of the hidrographic basin of Guaíba lake, State of Rio Grande do Sul, Brazil]. Revista Brasileira de Ornitologia 14(2): 101-115 [Portuguese with English abstract]. PDf fulltext
• Banks, R.C.; Cicero, C.; Dunn, J.L.; Kratter, A.W.; Ouellet, H.; Rasmussen, P.C.; Remsen, J.V. Jr.; Rising, J.A. & Stotz, D.F.) (2000): Forty-second supplement to the American Ornithologists' Union Check-list of North American Birds. Auk 117(3): 847–858. DOI: 10.1642/0004-8038(2000)117[0847:FSSTTA]2.0.CO;2 PDF fulltext
• BirdLife International (BLI) (2008). Bubo virginianus. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 18 November 2008.
• Dickerman, Robert W. (2004): Notes on the type of Bubo virginianus sclariventris. Bull. B.O.C. 124(1): 5-6. PDF fulltext
• Holt, Denver W.; Berkley, Regan; Deppe, Caroline; Enríquez Rocha, Paula L.; Olsen, Penny D.; Petersen, Julie L.; Rangel Salazar, José Luis; Segars, Kelley P. & Wood, Kristin L. (1999): 69. Great Horned Owl. In: del Hoyo, J.; Elliott, A. & Sargatal, J. (eds): Handbook of Birds of the World (Volume 5: Barn-owls to Hummingbirds): 185, plate 10. Lynx Edicions, Barcelona. ISBN 84-87334-25-3
• Howard, Hildegarde (1947): A preliminary survey of trends in avian evolution from Pleistocene to recent time. Condor 49(1): 10-13. DjVu fulltext PDF fulltext
• Houston, C. S., Smith, D. G. & Rohner, C. (1998): Great Horned Owl (Bubo virginianus). In: Poole, A. & Gill, F. (eds.): Birds of North America 372. Academy of Natural Sciences, Philadelphia, PA & American Ornithologists' Union, Washington, D.C. Online version, retrieved 2006-DEC-05. doi:10.2173/bna.372 (HTML preview)
• character sketches vol.1 1981

External links

• Cornell Lab of Ornithology: Great Horned Owl Species Account. Retrieved 2007-JAN-29.
• South Dakota Birds and Birding: Great Horned Owl Information and Photos. Retrieved 2007-JAN-29.
• USGS Patuxent Bird Identification InfoCenter: Great Horned Owl Information. Retrieved 2007-JAN-29.
• Great Horned Owl videos, photos & sounds on the Internet Bird Collection
• Free Online Video About Great Horned Owls from the science podcast "Terra: The Nature of Our World"
• Great Horned Owl Bird Sound