[7] The great horned owl was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae.

[8] Gmelin based his description on that of English naturalist George Edwards who had described and illustrated the great horned owl in 1747 in the second volume of his A Natural History of Uncommon Birds.

[12][13] One older study suggested that great horned and Eurasian eagle-owls may be conspecific, based on similarities in life history, geographic distribution, and appearance,[6] though this is not supported by genetic evidence, which places them in separate clades of their genus.

[14][12] Pleistocene era fossils have been found of Bubo owls in North America, which may either be distinct species or paleosubspecies, from as far east as Georgia, but predominantly in the Rocky Mountains and to the west of them.

[6][30] Great horned owls can apply at least 300 psi (2,100 kPa) of crushing power in their talons, a pressure considerably greater than the human hand is capable of exerting.

[36] They are visually highly adapted for nocturnal hunting and provide a wide, almost completely binocular field of view, a large corneal surface and a predominantly rod retina.

The peak wavelengths that are observed by the cones is 555 nm and the research suggests that the great horned owl has relatively weak color vision, especially compared to other bird species.

[62] In prairies, grasslands and deserts, they can successfully live year round as long as there are rocky canyons, steep gullies and/or wooded coulees with shade-giving trees to provide them shelter and nesting sites.

The highest threat level involves the spreading of wings, bill-clapping, hissing, higher-pitched screams of longer duration, with general body poised to strike with its feet at intruder.

[76] However, great horned owls can learn to target certain prey during daylight in the afternoon when it is more vulnerable, such as eastern fox squirrels (Sciurus niger) while they are building their leaf nests and chuckawallas (Sauromalus ater) sunning themselves on desert rocks.

[24][6][81] In fact, a healthy family of great horned owls can decimate a colony of field rats, thus potentially performing a key role in controlling a highly destructive pest.

In general larger sized than other rodent families, the species hunting range from the 62 g (2.2 oz) gray-collared chipmunk (Tamias cinereicollis) to the 5,775 g (12.732 lb) hoary marmot (Marmota caligata); thus, squirrels can provide a very fulfilling meal.

[7][15][94] An even larger rodent is sometimes attacked as prey by great horned owls, the North American porcupine (Erethizon dorsatum), in which average adults range from 4,500 to 9,000 g (9.9 to 19.8 lb).

[6] Further north in Colorado, in the absence of jackrabbits, the mountain cottontails falls to third place by number (12.9%) behind the northern pocket gopher (36.5%) and prairie vole (24.7%) but still dominates the biomass, making up about half.

[101] The dependence on lagomorphs also extends into Mexico, as in Baja California about a quarter of identified prey was black-tailed jackrabbit and either desert or the larger Mexican cottontail (Sylvilagus cunicularius).

A few cases of young or small dogs (Canis lupus familiaris)[121][122] and several of juvenile and adult cats (Felis silvestris catus) being killed by great horned owls have been reported.

[138] The wild turkey (Meleagris gallopavo), 4 to 8 kg (8.8 to 17.6 lb) on average between the sexes, is probably the largest bird the great horned owl hunts in which they kill adults.

[86] On Protection Island, Washington, where they are no native land mammals, rhinoceros auklets (Cerorhinca monocerata), both adults and nestlings, were the most numerous prey, present in 93% of 120 pellets.

[151][152][153][154] A study of food niche overlap between closely nested barn and great horned owls living in rural north-eastern Oregon identified voles as by far the most common prey.

[155] Although a stable and highly abundant food source, a diet consisting of primarily rats can be harmful to urban great horned owls due to bioaccumulation of rodenticides.

[178] During courtship in late fall or early winter, the male attracts the attention of his mate by hooting emphatically while leaning over (with the tail folded or cocked) and puffing up his white throat to look like a ball.

By late autumn, first-year birds look similar to adults but with a slightly warmer, reddish tinge, less well developed ear tufts and a smaller white throat patch.

The calls of the young increase rapidly in intensity, pitch and character, some juvenile males mimicking their father's hooting in fall but usually they conclude with various odd gurgling notes.

In Wisconsin, eggs in urban nests hatched a month earlier (January rather than February) than their counterparts in rural areas, probably due to increased protection from wind and cold.

[7][201][202] When a peregrine falcon repeatedly attacked a great horned owl near its nest along the Hudson River, it was apparently unable to dispatch the larger raptor despite several powerful strikes.

[205] Secondary poisoning from pest control efforts is widely reported variously due to anticoagulant rodenticides, strychnine, organophosphates (famphur applied topically to cattle (Bos primigenius taurus)), organochlorines, and PCBs.

[41][214] While at least the ospreys and peregrines have rebounded admirably nonetheless, bird and mammal species that are much rarer overall sometimes fall prey to great horned owls, many in which even sporadic losses can be devastating.

Among the species considered threatened, endangered or critically endangered by the IUCN which are also known to be killed by great horned owls are Townsend's ground squirrels (Urocitellus townsendii),[101] Pacific pocket mice (Perognathus pacificus),[215] giant kangaroo rats,[216] Stephens' kangaroo rat (Dipodomys stephensi),[217] black-footed ferrets,[218] greater and lesser prairie chickens,[219][220] marbled murrelets (Brachyramphus marmoratus),[221] ivory-billed woodpeckers, Florida scrub jays (Aphelocoma coerulescens),[222] pinyon jays,[223] Kirtland's warblers (Setophaga kirtlandii)[224] and rusty blackbirds (Euphagus carolinus).

[226] On the contrary, William J. Baerg compared behaviorally his captive-raised great horned owls to parrots, which are famously intelligent birds, although not as often playful: "It knows its keeper and usually accepts whatever he wishes to do with a good deal of tolerance.

They will only follow cues when conditioned from an early age but rarely with the same level of success seen in some diurnal birds of prey trained for falconry or entertainment, although this does not necessarily correlate with intelligence as posited by Errington.