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Great horned owl
The great horned owl (''Bubo virginianus''), also known as the tiger owl (originally derived from early naturalists' description as the "winged tiger" or "tiger of the air") or the hoot owl,〔Austing, G.R. & Holt, Jr., J.B. (1966). ''The World of the Great Horned Owl''. Lippingcott Company, Philadelphia (3rd printing.)〕 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 appears to be rabbits and hares, rats and mice and voles, although it freely hunts any animal it can overtake, primarily other rodents and small mammals, but also larger mid-sized mammals, various birds, reptiles, amphibians and invertebrates. In ornithological study, the great horned owl is often compared to the Eurasian eagle-owl (''Bubo bubo''), a closely related species which, despite the latter's notably larger size, occupies the same ecological niche in Eurasia, and the red-tailed hawk (''Buteo jamaicensis''), with which it often shares similar habitat, prey and nesting habits by day and is thus something of a diurnal ecological equivalent.〔Voous, K.H. 1988. ''Owls of the Northern Hemisphere''. The MIT Press, 0262220350.〕 The great horned owl is one of the earliest nesting birds in North America, often laying eggs weeks or even months before other raptorial birds.〔Bent, A. C. 1938. ''Life histories of North American birds of prey, Part 2''. U.S. National Museum Bulletin 170:295-357.〕
==Description==
The great horned owl is generally colored for camouflage.〔 The underparts of the species are usually light with some brown horizontal barring; the upper parts and upper wings are generally a mottled brown usually baring heavy, complex darker markings. All subspecies are darkly barred to some extent along the sides as well. There is a variable sized white patch on the throat. The white throat may continue as a streak running down the middle of the breast even when the birds are not displaying, which in particularly pale individuals can widen at the belly into a large white area. South American horned owls typically have a smaller white throat patch, often unseen unless actively displaying, and rarely display the white area on the chest. This species' "horns" are neither ears nor horns, simply tufts of feathers. Ear tufts are shared by all members of its genus, as well as almost exactly half of all the more than 200 living owl species, but are absent in the African fishing owls (which are still sometimes treated separately in the genus ''Scotopelia''). The snowy owl (''Bubo scandiacus'') has vestigial ear-tufts which usually are not visible (the tufts of the snowy measure up to when erected, less than half the length of the ear tufts of a northern great horned owl) and many other "eared" owl species, unlike the great horned, can appear tuft-less when relaxed such as many of the nearly 70 species of Old World scops owls and New World screech owls (2 species from the latter genera completely lack ear tufts). The purpose of ear tufts is not fully understood, although the theory that they serve as a visual cue in territorial and socio-sexual interactions with other owls is now generally considered more valid than other theories such as they are designed to mimic mammalian carnivores or provide camouflage.〔
All great horned owls have a facial disc, which (although not as deep set as some ''Strix'' and ''Aegolius'' species) is well demarked due to a dark rim which culminates in bold, blackish brackets at the sides of the disc. The facial disc may be reddish, brown or gray in color, showing considerable geographic, racial and individual variation.〔''Owls of the World: A Photographic Guide'' by Mikkola, H. Firefly Books (2012), ISBN 9781770851368〕 There are individual and regional variations in overall color as well; birds from the subarctic are a washed-out, light-buff color, while those from the Pacific Coast of North America, Central America and much of South America can be a dark brownish color overlaid with blackish blotching. The skin of the feet and legs, though almost entirely obscured by feathers, is black. The bill is dark gunmetal-gray, as are the talons.
The great horned owl is the heaviest extant owl in Central and South America and is the second heaviest owl in North America, after the closely related but very different looking snowy owl.〔〔 However, the great horned owl is quite variable in size across its range. Clinal variation in size, more-or-less well studied in North America among the less variable measurements of skeleton, with interior Alaska and Ontario populations being largest and populations in California and Texas being smallest, though those from the Yucatán Peninsula and Baja California appear to be even smaller.〔Mcgillivray, W. B. 1989. ''Geographic variation in size and reverse size dimorphism of the Great Horned Owl in North America''. Condor 91:777-786.〕〔Webster, J. D. and R. T. Orr. 1958. ''Variation in the Great Horned Owls of Middle America''. Auk 75:134-142.〕 Overall, adult great horned owls range in length from and possess a wingspan of .〔Houston, C. Stuart, Dwight G. Smith and Christoph Rohner. 1998. ''Great Horned Owl (Bubo virginianus)'', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online.〕〔(【引用サイトリンク】title=Great Horned Owl – Bubo virginianus – Information, Pictures, Sounds )〕 Females are invariably somewhat larger than males. 1761 specimens (mainly museum specimens) of all North American subspecies were found to possess a mean weight of for the females and for the males.〔Craighead, J. J. and F. C. Craighead, Jr. 1956. ''Hawks, owls and wildlife''. Stackpole Co. Harrisburg, PA.〕〔Snyder, N. F. R. and J. W. Wiley. 1976. ''Sexual size dimorphism in hawks and owls of North America''. AOU Ornithological Monograph, 20:1-96.〕 Depending on subspecies, the great horned owl can weigh from , with more details on the weights of the races given below.〔''CRC Handbook of Avian Body Masses'' by John B. Dunning Jr. (Editor). CRC Press (1992), ISBN 978-0-8493-4258-5.〕 An average adult between both sexes in North America measures around long with a wingspan and weighs about .
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