View source for Great horned owl

{{Short description|Species of owl}}
{{Speciesbox
| image = Bubo virginianus 06.jpg
| fossil_range = {{Fossil range|Pleistocene|present}}
| image_caption = {{Plainlist|
*Common great horned owl
*''B. v. virginianus''
}}
| image2 = Bubo virginianus -Canada-6.jpg
| image2_caption = {{Plainlist|
*Coastal great horned owl
*''B. v. saturatus''
*[[Reifel Migratory Bird Sanctuary]], [[Delta, British Columbia]], Canada
}}
| status = LC
| status_system = IUCN3.1
| status_ref = <ref name=IUCN>{{cite iucn | author =BirdLife International | title = ''Bubo virginianus'' | article-number =e.T61752071A132039486  | year =2018 | doi = 10.2305/IUCN.UK.2018-2.RLTS.T61752071A132039486.en | access-date = 20 February 2022 }}</ref>
| status2 = CITES_A2 
| status2_system = CITES 
| status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>
| genus = Bubo
| species = virginianus
| authority = ([[Johann Friedrich Gmelin|Gmelin]], 1788)
| range_map = Bubo_virginianus_dis.png
| range_map_caption = Global range (all year) of ''B. virginianus''
| subdivision_ranks = Subspecies
| subdivision = About 12, see text
| synonyms = {{Plainlist|
*''Strix virginiana'' <small>Gmelin, 1788</small>
*and see [[#Subspecies|text]]
}}
}}

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")<ref>{{Cite journal |last=Seton |first=Ernest E. T. |date=January 1885 |title=Manitoban Notes |url=https://www.jstor.org/stable/pdf/4625166.pdf |journal=The Auk |volume=2 |issue=1 |pages=21–24 |doi=10.2307/4625166 |jstor=4625166 |via= }}</ref> or the '''hoot owl''',<ref name= Austing>{{cite book |last1=Austing |first1=G.R. |last2=Holt |first2=Jr., J.B. |year=1966 |title=The World of the Great Horned Owl |publisher=Lippingcott Company |location=Philadelphia |asin=B0006BN8QG}}</ref> 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.<ref name=Cornell>{{cite web|title=Great Horned Owl|url=http://www.allaboutbirds.org/guide/great_horned_owl/id%7CCornell-|publisher=The Cornell Lab of Ornithology|access-date=21 March 2013|archive-url=https://web.archive.org/web/20170705212240/https://www.allaboutbirds.org/guide/great_horned_owl/id%7CCornell-|archive-date=5 July 2017}}</ref> Its diet consists primarily of [[Leporidae|rabbits and hare]]s, [[New World rats and mice|rats and mice]], and [[vole]]s; it remains one of the few regular predators of [[skunk]]. Hunting also includes [[rodent]]s, larger mid-sized [[mammal]]s, [[bird]]s, [[reptile]]s, [[amphibian]]s, and [[invertebrate]]s. 

In ornithological study, the great horned owl is often compared to the [[Eurasian eagle-owl]] (''Bubo bubo''), a closely related species, which occupies the same ecological niche in [[Eurasia]] despite its notably larger size. The great horned owl is also compared to the [[red-tailed hawk]] (''Buteo jamaicensis''), with which it often shares similar habitat, prey, and nesting habits by day; thus the red-tailed hawk is something of a diurnal ecological equivalent.<ref name="Voous">{{cite book |last1=Voous |first1=K.H. |year=1988 |title=Owls of the Northern Hemisphere |publisher=MIT Press |isbn=0-262-22035-0}}</ref> 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.<ref name="Bent">{{cite book | last=Bent | first=Arthur Cleveland | author-link=Arthur Cleveland Bent | date=1938 | title=Life Histories of North American Birds of Prey | volume=2: Orders Falconiformes and Strigiformes | series=Bulletin of the United States National Museum, No. 170 | location=Washington, DC | publisher=Smithsonian Institution | pages=295–348 | hdl=10088/10016 | url=https://repository.si.edu/handle/10088/10016 }}</ref>

==Taxonomy==
[[File:Lechuzon orejudo (zoológico de Paraguaná).jpg|thumb|''Bubo virginianus nacurutu'']]
The great horned owl was [[Species description|formally described]] in 1788 by the German naturalist [[Johann Friedrich Gmelin]] in his revised and expanded edition of [[Carl Linnaeus]]'s ''[[Systema Naturae]]''. He placed it with the other owls in the [[genus]] ''[[Strix (bird)|Strix]]'' and coined the [[binomial nomenclature|binomial name]] ''Strix virginia''.<ref>{{ cite book | last=Gmelin | first=Johann Friedrich | author-link=Johann Friedrich Gmelin| year=1788 | title=Systema naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis | edition=13th | volume=1, Part 1 | language=Latin | location=Lipsiae [Leipzig] | publisher=Georg. Emanuel. Beer | page=287 | url=https://www.biodiversitylibrary.org/page/2896887 }}</ref> Gmelin based his description on that of English naturalist [[George Edwards (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''. Edwards had seen a live specimen from [[Virginia]] at the [[Chiswick House|house]] of the [[Richard Boyle, 3rd Earl of Burlington|Earl of Burlington]] in [[Chiswick]]. Edwards also owned a preserved specimen, and another specimen formed part of the [[Leverian collection]].<ref>{{ cite book | last=Edwards | first=George | author-link=George Edwards (naturalist) | year=1747 | title=A Natural History of Uncommon Birds | location=London | publisher=Printed for the author at the College of Physicians | volume=Part 2 | page=60; Plate 60 | url=https://www.biodiversitylibrary.org/page/50240730 }}</ref> The great horned owl  is now placed in the genus ''[[Horned owl|Bubo]]'' that was introduced in 1805 by [[André Marie Constant Duméril|André Duméril]].<ref>{{ cite book | last=Duméril | first=A. M. Constant | author-link=André Marie Constant Duméril | date=1805 | title=Zoologie analytique: ou, Méthode naturelle de classification des animaux; endue plus facile a l'aide de tableaux synoptiques  | language=French | location=Paris | publisher=Allais | page=34 | url=https://www.biodiversitylibrary.org/page/12052585 }} The book bears the date of 1806 on the title page but was actually published in 1805. See: {{cite journal| last=Gregory | first=Steven M.S. | year=2010 | title=The two 'editions' of Duméril's ''Zoologie analytique'', and the potential confusion caused by Froriep's translation ''Analytische Zoologie'' | journal=Zoological Bibliography | volume=1 | issue=1 | pages=6–8 | url=https://iucn-tftsg.org/wp-content/uploads/file/Articles/Gregory_2010.pdf }}</ref><ref name=ioc>{{cite web| editor1-last=Gill | editor1-first=Frank | editor1-link=Frank Gill (ornithologist) | editor2-last=Donsker | editor2-first=David | editor3-last=Rasmussen | editor3-first=Pamela | editor3-link=Pamela Rasmussen | date=August 2022 | title=Owls | work=IOC World Bird List Version 12.2 | url=https://www.worldbirdnames.org/bow/owls/ | publisher=International Ornithologists' Union | access-date=24 December 2022 }}</ref>

The great horned owl represents one of the one or two radiations of the genus across the [[Beringia|Bering land bridge]] to the [[Americas]]. Whereas the [[lesser horned owl]] clearly divided once the owl had spread through the Americas, the consensus seems to be that the [[snowy owl]] and the great horned owl divided back in Eurasia and the snowy then spread back over the [[Arctic]] through northernmost North America separately from the radiation of the greater and lesser horned owls.<ref name= Konig/><ref name= Potapov>{{cite book |last1=Potapov |first1=E. |last2=Sale |first2=R. |year=2013 |title=The Snowy Owl |series=Poyser Monographs |publisher=A&C Black |isbn=978-0-7136-8817-7}}</ref> One older study suggested that great horned and Eurasian eagle-owls may be conspecific, based on similarities in life history, geographic distribution, and appearance,<ref name= Voous/> though this is not supported by genetic evidence, which places them in separate clades of their genus.<ref name=Omote>{{cite journal |author1=Omote, K. |author2= Nishida, C. |author3=Dick, M. H. |author4=Masuda, R. |year=2013 |title=Limited phylogenetic distribution of a long tandem-repeat cluster in the mitochondrial control region in Bubo (Aves, Strigidae) and cluster variation in Blakiston's fish owl (''Bubo blakistoni'') |journal=Molecular Phylogenetics and Evolution |volume=66 |issue=3 |pages=889–897 |doi=10.1016/j.ympev.2012.11.015 |pmid= 23211719 |bibcode= 2013MolPE..66..889O }}</ref> Genetic testing indicates that the lesser horned owl, and then the snowy owl, not the Eurasian eagle-owl, are the most closely related living species.<ref name=Omote/><ref name="Konig" /> [[Pleistocene|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 (U.S. state)|Georgia]], but predominantly in the [[Rocky Mountains]] and to the west of them.<ref name="Houston" /><ref>{{cite journal |last1=Brodkorb |first1=P. |year=1971 |title=Catalogue of fossil birds, Part 4 (Columbiformes through Piciformes) |journal=Bulletin of the Florida State Museum, Biological Science |volume=15 |issue=4 |url=http://palmm.digital.flvc.org/islandora/object/uf%3A40247#page/fmnh/mode/1up}}</ref> Almost all fossils indicate these owls were larger than modern great horned owls.<ref>{{cite journal |last1=Miller |first1=L. H. |year=1911 |title=Avifauna of the Pleistocene cave deposits of California |journal=University of California Bulletin, Department of Geology |volume=6 |pages=385–400 |url=https://searchworks.stanford.edu/view/76244}}</ref><ref>{{cite journal |last1=Olson |first1=S. L. |year=1984 |title=A very large enigmatic owl from the late Pleistocene at Ladds, Georgia |journal=Special Publication, Carnegie Museum of Natural History |volume=8 |pages=44–46}}</ref>

A large number of [[subspecies]], more than 20 altogether, have been named. However, many of these are not true subspecies and only examples of individual or [[Cline (population genetics)|clinal]] variation. Subspecies differences are mainly in color and size and generally follow [[Gloger's Rule|Gloger's]] and [[Bergmann's rule]]s:<ref name= Houston/> The most conservative treatments of great horned owl subspecies may describe as few as 10,<ref name= Konig/> although an intermediate number is typical in most writings.<ref name= Houston/>

Fifteen subspecies are currently recognised:<ref name=ioc/>
* ''B. v. algistus'' ([[Harry C. Oberholser|Oberholser]], 1904) – west Alaska
* ''B. v. lagophonus'' (Oberholser, 1904) – central Alaska to northeast Oregon, Idaho and northwest Montana (US)
* ''B. v. saturatus'' [[Robert Ridgway|Ridgway]], 1877 – coastal southeast Alaska to coastal north California (US)
* ''B. v. pacificus'' [[John Cassin|Cassin]], 1854 – coastal central California (US) to northwest [[Baja California]] (Mexico)
* ''B. v. subarcticus'' Hoy, PR, 1853 – central west Canada to north Idaho (US)
* ''B. v. pallescens'' [[Witmer Stone|Stone]], 1897 – southwest US to south Mexico
* ''B. v. pinorum'' Dickerman & Johnson, AB, 2008 – south Idaho to north Arizona and north New Mexico (US)
* ''B. v. heterocnemis'' (Oberholser, 1904) – northeast Canada to the [[Great Lakes]] region
* ''B. v. virginianus'' ([[Johann Friedrich Gmelin|Gmelin, JF]], 1788) – southeast Canada to central, east US
* ''B. v. elachistus'' [[William Brewster (ornithologist)|Brewster]], 1902 – south [[Baja California]] (Mexico)
* ''B. v. mayensis'' [[Edward William Nelson|Nelson]], 1901 – [[Yucatán Peninsula]] (southeast Mexico)
* ''B. v. mesembrinus'' (Oberholser, 1904) – south Mexico to west Panama
* ''B. v. nigrescens'' [[Hans von Berlepsch|Berlepsch]], 1884 – Colombia to northwest Peru
* ''B. v. nacurutu'' ([[Louis Pierre Vieillot|Vieillot]], 1817) – east Colombia through the Guianas to north, east Brazil, Argentina, Bolivia and central Peru
* ''B. v. deserti'' [[Othmar Reiser|Reiser]], 1905 – northeast Brazil (central north Bahia)

==Description==
The great horned owl is generally colored for camouflage.<ref name= Bent/> 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 bearing heavy, complex, darker markings. All subspecies are darkly barred to some extent along the sides. 
[[File:Great Horned Owl (8457397428).jpg|thumb|Great horned owl showing much of its camouflage pattern/color]]
A variable-sized white patch  is seen 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 great horned owl]]s typically have a smaller white throat patch, often unseen unless actively displaying, and rarely display the white area on the chest.<ref name= Voous/> 

Individual and regional variations in overall color occur, with birds from the [[subarctic]] showing 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. Even tropical great horned owls have feathered legs and feet. The feathers on the feet of the great horned owl are the second-longest known in any owl (after the [[snowy owl]]).<ref name="Voous" /> The bill is dark gunmetal-gray, as are the talons.<ref name="Konig">{{cite book |last=König |first=Claus |title=Owls of the World |year=2008 |publisher=Christopher Helm |location=London |isbn=978-1-4081-0884-0 |edition=2nd |author2=Weick, Friedhelm }}</ref>

All great horned owls have a [[facial disc]]. This can be reddish, brown, or gray in color (depending on geographical and racial variation) and is demarked by a dark rim culminating in bold, blackish side brackets.<ref name= Mikkola>{{cite book |title=Owls of the World: A Photographic Guide |last1=Mikkola |first1=H. |publisher=Firefly Books |year=2012 |isbn=978-1-77085-136-8}}</ref> This species' eyebrow-like "horns" are [[ear tuft|tufts of feathers]],<ref>{{Cite web |date=2022-08-08 |title=Great Horned Owl –Sierra Nevada Aquatic Research Laboratory |url=https://snarl.nrs.ucsb.edu/resources/great-horned-owl/ |access-date=2024-08-13 |language=en-US}}</ref> called plumicorns. The purpose of plumicorns is not fully understood, but the hypothesis that they serve as a visual cue in territorial and sociosexual interactions with other owls is generally accepted.<ref name= Voous/>

===Physiology and measurements===
[[File:Great Horned Owl (6019438860).jpg|thumb|The eyes of great horned owls are among the proportionally largest of terrestrial vertebrates.]]
The great horned owl is the heaviest extant owl in [[Central America|Central]] and South America and is the second-heaviest owl in North America, after the closely related but very different-looking snowy owl.<ref name= Bent/><ref name= Konig/> It is heavily built, with a barrel-shaped body, a large head, and broad wings.<ref name= Konig/> Its size can vary considerably across its range, with populations in interior [[Alaska]] and [[Ontario]] being largest and populations in [[California]] and [[Texas]] being smallest, though those from the [[Yucatán Peninsula]] and [[Baja California]] appear to be even smaller.<ref name= Mcgillivray>{{cite journal |last1=Mcgillivray |first1=W. B. |year=1989 |title=Geographic variation in size and reverse size dimorphism of the Great Horned Owl in North America |journal=Condor |volume=91 |issue=4 |pages=777–786 |doi=10.2307/1368060|jstor=1368060 }}</ref><ref name= Webster>{{cite journal |last1=Webster |first1=J. D. |first2=R. T. |last2=Orr |year=1958 |title=Variation in the Great Horned Owls of Middle America |journal=Auk |volume=75 |issue=2 |pages=134–142 |doi=10.2307/4081882|jstor=4081882 }}</ref> Adult great horned owls range in length from {{convert|43|to|64|cm|in|abbr=on}}, with an average of {{convert|55|cm|in|abbr=on}}, and possess a wingspan of {{convert|91|to|153|cm|ftin|abbr=on}}, with an average of {{convert|122|cm|in|abbr=on}}. Females are somewhat larger than males.<ref name= Houston>{{cite journal |last1=Artuso |first1=C. |first2=C. S. |last2=Houston |first3=D. G. |last3=Smith |first4=C. |last4=Rohner |year=2020 |title=Great Horned Owl (''Bubo virginianus''), version 1.0 |journal=Birds of the World |editor-first1=A. F. |editor-last1=Poole |publisher=Cornell Lab of Ornithology |location=Ithaca, NY |doi=10.2173/bow.grhowl.01 |url=https://birdsoftheworld.org/bow/species/grhowl/cur/introduction|url-access=subscription }}</ref><ref name="owlpages.com">{{cite web|url=http://www.owlpages.com/owls.php?genus=Bubo&species=virginianus |title=Great Horned Owl – Bubo virginianus – Information, Pictures, Sounds |publisher=Owlpages.com |access-date=2012-02-09}}</ref> Mean body weight is {{convert|1608|g|lb|abbr=on}} for females and {{convert|1224|g|lb|abbr=on}} for males.<ref name= Craighead>{{cite book |last1=Craighead |first1=J. J. | first2=F. C. Jr. | last2=Craighead |year=1956 |title=Hawks, owls and wildlife |publisher=Stackpole Co. |location=Harrisburg, PA |isbn=0-486-22123-7}}</ref><ref name= Snyder>{{cite journal |last1=Snyder |first1=N. F. R. |first2=J. W. |last2=Wiley |year=1976 |title=Sexual size dimorphism in hawks and owls of North America |journal=Ornithological Monographs |volume=20 |issue=20 |pages=1–96 |doi=10.2307/40166710|jstor=40166710 }}</ref> Depending on subspecies, maximum weight can reach {{convert|2503|g|lb|abbr=on}}.<ref name = "CRC">{{cite book |title=CRC Handbook of Avian Body Masses |editor-first1=John B. Jr. |editor-last1=Dunning |publisher=CRC Press |year=1992 |isbn=978-0-8493-4258-5}}.</ref>
[[File:Great Horned Owl in Flight C 9508.jpg|thumb|Great horned owl wing]]
The [[Wing chord (biology)|wing chord]] length is {{convert|297|-|400|mm|in|abbr=on}}.<ref name= Earhart>{{cite journal |last1=Earhart |first1=C. M. |first2=N. K. |last2=Johnson |year=1970 |title=Size dimorphism and food habits of North American Owls |journal=Condor |volume=72 |issue=3 |pages=251–264 |doi=10.2307/1366002|jstor=1366002 }}</ref> The [[wing loading]], the measured wing area compared to weight, is high, meaning the wings are relatively small in surface area for the bird's weight; the species' wing loading has been described as proportionately the highest among raptors.<ref name= Mikkola/><ref name= Johnson>{{cite journal |last1=Johnson |first1=D. H. |year=1998 |title=Wing loading in 15 species of North American owls |pages=553–561 |journal=Biology and Conservation of Owls of the Northern Hemisphere, 2nd International Symposium, Gen. Tech. Rep. NC-190 |volume=190 |editor-last1=Duncan |editor-first1=J. R. |editor-first2=D. H. |editor-last2=Johnson |editor-first3=T. H. |editor-last3=Nicholls |publisher=U.S. Dept. of Agriculture Forest Service, North Central Forest Experiment Station |location=St. Paul, MN |url=https://research.fs.usda.gov/treesearch/15634}}</ref> The [[tail]], being relatively short as is typical of most owls, is {{convert|175|to|252|mm|in|abbr=on}} long. Like other owl species, the great horned owl is capable of "silent flight", which is the way owls fly while making almost no discernable noise, despite their large size. 
This is made possible thanks to three main components of the owl's wing structure. The leading edge of their feathers have serrations that help to disrupt the turbulence generated by wing flapping, then the softer feathers help deaden the sound, and finally the trailing fringe of the feathers works to finish cutting the sounds made by flight. The structure of the great horned owl wing also allows it to fly at a very low speed for the size of the species, as slow as 2 miles per hour when they are gliding on breezes.<ref>{{Cite web|url=https://www.audubon.org/news/the-silent-flight-owls-explained|title=The Silent Flight of Owls, Explained|date=2017-07-28|website=Audubon|language=en|access-date=2020-02-21}}</ref>
[[File:Talons, Great Horned Owl.jpg|thumb|Great horned owl (Canada)]]
The legs, feet, and talons are large and powerful. [[Tarsus (skeleton)|Tarsal length]] is {{convert|54|-|80|mm|in|abbr=on}}.<ref name=Konig/> The average foot span of a fully spread foot, from talon to talon, is around {{convert|20|cm|in|abbr=on}}, as compared to {{convert|8|cm|in|abbr=on}} in [[long-eared owl]]s, {{convert|13|to|15|cm|in|abbr=on}} in [[American barn owl|barn owl]]s, and {{convert|18|cm|in|abbr=on}} in the [[great grey owl]].<ref name= Voous/><ref name= Marti>{{cite journal |last1=Marti |first1=C. D. |year=1974 |title=Feeding ecology of four sympatric owls |journal=Condor |volume=76 |issue=1 |pages=45–61 |doi=10.2307/1365983|jstor=1365983 }}</ref> Great horned owls can apply at least {{cvt|300|psi}} of crushing power in their talons, a pressure considerably greater than the human hand is capable of exerting. In some big females, the gripping power of the great horned owl may be comparable to much larger raptor species such as the [[golden eagle]].<ref name=Lubbock>{{cite news|last=Lee|first=Carol|title=Powerful feet and talons help birds of prey make their living|url=http://lubbockonline.com/stories/032606/gue_032606062.shtml|access-date=21 March 2013|newspaper=Lubbock Avalanche-Journal|date=March 26, 2006|archive-date=3 July 2017|archive-url=https://web.archive.org/web/20170703161741/http://lubbockonline.com/stories/032606/gue_032606062.shtml}}</ref>

The hard, inflexible [[Beak|bill]] of the great horned owl is {{convert|3.3|-|5.2|cm|in|abbr=on}} long, although the [[Culmen (bird)|culmen]], the exposed bill portion as measured along the top of the beak, is only {{convert|2.1|to|3.3|cm|in|abbr=on}}.<ref name= Ridgway>{{cite journal |last1=Ridgway |first1=Robert |year=1919 |title=The birds of North and Middle America: A descriptive catalogue of the higher groups, genera, species, and subspecies of birds known to occur in North America, from the Arctic lands to the Isthmus of Panama, the West Indies and other islands of the Caribbean Sea, and the Galapagos Archipelago pt. 8: Families Jacanidae, Oedicnemidae, Haematopodidae, Arenariidae, Aphrizidae, Charadriidae, Scolopacidae, Phalaropodidae, Recurvirostridae, Rynchopidae, Sternidae, Laridae, Stercorariidae, Alcidae. |journal=Bulletin of the United States National Museum |issue=50 |pages=i–852 |doi=10.5479/si.03629236.50.i}}</ref>

The outer ear openings, which are concealed by feathers on the sides of the head, are relatively smaller than those of the Eurasian eagle owl, being {{convert|2.3|cm|in|abbr=on}} in vertical axis, with the left ear slightly larger than the right.<ref>{{cite journal |last1=Norberg |first1=R.A. |year=1977 |title=Occurrence in independent evolution of bilateral ear asymmetry in owls and implications in owl taxonomy |journal= Philosophical Transactions of the Royal Society of London, Series B|volume=280 |issue=973 |pages=375–408|doi=10.1098/rstb.1977.0116 |bibcode=1977RSPTB.280..375N }}</ref> Like most exclusively (or near exclusively) nocturnal species, the great horned owl has asymmetrical ear holes that allow for the triangulation of sounds when hunting in the dark. The different-height holes, while still close together, are differentiated enough that the owl is able to use the timing and direction of the sound waves hitting each hole to precisely locate prey even if the prey is located under cover such as snow. The disc-like shape of their faces also helps to direct the sounds they hear toward their ears. While the true nature/purpose of the ear tufts that are present on the great horned owl is unknown, researchers agree that the tufts do not play any role in the hearing ability of the owl. It is estimated that their hearing is up to ten times that of a human being.<ref>{{Cite journal|last=Traynor|first=Robert M.|date=September 1997|title=The missing link for success in hearing aid fittings|journal=The Hearing Journal|volume=50|issue=9|page=10|doi=10.1097/00025572-199709000-00001|s2cid=147068859|issn=0745-7472|doi-access=free}}</ref>

The great horned owl's eyes, just slightly smaller than the eyes of a [[human being]], are large even for an owl and rank proportionately among the largest eyes of all terrestrial vertebrates.<ref>{{cite journal |last1=Hall |first1=M. I. |last2=Heesy |first2=C. P. |year=2011 |title=Eye size, flight speed and Leuckart's Law in birds |journal=Journal of Zoology |volume=283 |issue=4 |pages=291–297 |doi=10.1111/j.1469-7998.2010.00771.x|s2cid=81153664 }}</ref> The great horned owl has cylindrical eyes which creates more distance from the lens of the eye to the retina, which allows it to act more like a telephoto lens for farther distance sight compared to that possible from round eyes.<ref>{{Cite web|url=https://greathornedowl.net/great-horned-owl-eyes/|title=Great Horned Owl Eyes – How Far Can a Great Horned Owl See?|last=Waleed |date=2018-08-24|website=Great Horned Owl|language=en-US|access-date=2020-02-21}}</ref> They are visually highly adapted for nocturnal hunting and provide a wide, almost completely binocular field of view, a large [[cornea]]l surface and a predominantly rod [[retina]].<ref>{{cite journal |last1=Fite |first1=K. V. |year=1973 |title=Anatomical and behavioral correlates of visual acuity in the Great Horned Owl |journal=Vision Research |volume=13 |issue=2 |pages=219–230 |doi=10.1016/0042-6989(73)90101-6 |pmid=4692516}}</ref> 

The great horned owl's eye contains both rods and cones like most species that see in color, but the vision of a great horned owl closely resembles that of many other nocturnal species. The peak wavelengths that are observed by the cones is 555&nbsp;nm, and the research suggests that the great horned owl has relatively weak color vision, especially compared to other bird species. Despite (or perhaps as a result of) the poorer sense of color vision, the owl manages to have excellent night vision.<ref>{{Cite journal|last1=Jacobs|first1=Gerald H.|last2=Crognale|first2=Michael|last3=Fenwick|first3=John|date=May 1987|title=Cone Pigment of the Great Horned Owl|url=https://academic.oup.com/condor/article/89/2/434-436/5188961|journal=The Condor|volume=89|issue=2|page=434|doi=10.2307/1368502|jstor=1368502|url-access=subscription}}</ref> Instead of turning its eyes, an owl must turn its whole head, and the great horned owl can rotate its neck 270°. The [[Iris (anatomy)|iris]] is yellow, except in the amber-eyed [[South American great horned owl]] (''B. v. nacurutu'').

===Calls===
[[File:Bubo virginianus - Great Horned Owl XC450919.mp3|right|thumb|Audio great horned owl]]
The great horned owl's [[Bird vocalization|song]] is normally a low-pitched but loud {{Not a typo|''ho-ho-hoo hoo hoo''}} (or also transcribed as {{Not a typo|''bu-bubu booh''}}, {{Not a typo|''who-hoo-ho-oo''}} or {{Not a typo|''who-ho-o-o''}}, {{Not a typo|''whoo-hoo-o-o''}}, {{Not a typo|''whoo''}}) and can last for four or five syllables. The call is resonant and has warranted descriptions as varied as "solemn" and "terrifying".<ref name= Voous/><ref name= Bent/> The female's call is higher and rises in pitch at the end of the call. Female vocalizations are higher in pitch because of a smaller [[Syrinx (bird anatomy)|syrinx]] in the larger sex.<ref>{{cite journal |last1=Miller |first1=A. H. |year=1934 |title=The vocal apparatus of some North American owls |journal=Condor |volume=36 |issue=5 |pages=204–213 |doi=10.2307/1363856|jstor=1363856 }}</ref> Calling seems to peak after rather than before midnight.<ref>{{cite journal |last1=Morrell |first1=T. E. |first2=R. H. |last2=Yahner |first3=W. L. |last3=Harkness |year=1991 |title=Factors affecting detection of Great Horned Owls by using broadcast vocalizations |journal=Wildlife Society Bulletin |volume=19 |issue=4 |pages=481–488 |jstor=3782162}}</ref><ref name= Johnson2>{{cite thesis |last1=Johnson |first1=D. H. |year=1993 |title=Spotted Owls, Great Horned Owls, and forest fragmentation in the Central Oregon Cascades |type=Master's Thesis |publisher=Oregon State University |location=Corvallis |url=https://andrewsforest.oregonstate.edu/publications/1378}}</ref> Usually, territorial hooting decreases in February or March at the onset of egg laying.<ref name= Petersen>{{cite journal |last1=Petersen |first1=L. |year=1979 |title=Ecology of Great Horned Owls and Red-tailed Hawks in southeastern Wisconsin |journal=Wisconsin Department of Natural Resources Technical Bulletin |volume=111}}</ref> 

On occasion, this species exhibits "an indescribable assemblage of hoots, chuckles, screeches, and squawks, given so rapidly and disconnectedly that the effect is both startling and amusing".<ref name="Baumgartner">{{cite journal |last1=Baumgartner |first1=F. M. |year=1938 |title=Courtship and nesting of the great horned owls |journal=The Wilson Bulletin |pages=274–285}}</ref> Descriptions of some of these odd sounds including a growling {{Not a typo|''krrooo-ooo''}} note pair, a laughing {{Not a typo|''whar, whah, wha-a-a-a-ah''}}, a high-pitched {{Not a typo|''ank, ank, ank''}}; a weak, soft {{Not a typo|''erk, erk''}}, a [[cat]]-like {{Not a typo|''meee-owwwwww''}}, a [[hawk]]-like note of {{Not a typo|''ke-yah, ke-yah''}}, and a [[nighthawk]]-like {{Not a typo|''peent''}}. These vocalizations may be variously uttered when the birds are disturbed and angered at the nest (frequently preceding an attack on an interloping human or other animal), represent the vocal development of young owls, or are given during courtship and during territorial disputes with other owls.<ref name="Bent" /><ref name="Houston" /><ref name="Rohner">{{cite journal |last1=Rohner |first1=C. |year=1996 |title=The numerical response of Great Horned Owls to the snowshoe hare cycle: consequences of non-territorial 'floaters' on demography |journal=Journal of Animal Ecology |volume=65 |issue=3 |pages=359–370 |doi=10.2307/5882|jstor=5882 |bibcode=1996JAnEc..65..359R }}</ref> Young owls still in the care of their parents make loud, persistent hissing or loud, piercing screeching sounds that are often confused with the calls of the barn owl.<ref name="Konig" />

===Subspecies===
'''Common/eastern great horned owl''' (''Bubo virginianus virginianus'')
:[[Eastern United States]] eastwards from at least as far west as [[Minnesota]] to [[Texas]]; northeastwards in distribution to southern [[Quebec]], southern [[Ontario]], [[Nova Scotia]] and [[Prince Edward Island]]. Resident all-year.<ref name= Houston/> The race ''B. v. mesembrinus'' from Central America south of the [[Isthmus of Tehuantepec]], may be merely a southerly leg of this race, as its coloring is almost exactly the same as ''virginianus'', although with rather smaller body size. However, ''mesembrinus'' type owls are discontinuous in range, with only paler owls from ''pallescens'' and ''mayensis'' found in the in-between range before the northern ''virginianus'' reappears back up in [[South Texas]].<ref name= Konig/><ref name= Webster/>
:The "nominate race" is a medium-hued form, neither darkly saturated nor strikingly pale. Darker gray or somewhat paler individuals are known. It tends to be richly tinged with rufous and barred distinctly blackish-brown below with rather soft contrast. The feet can range from tawny to buff to creamy and are the legs are typically barred dark to a moderate extent. The facial disc is often a solid cinnamon-red color. This is mid-to-large race, with a [[Wing chord (biology)|wing chord]] length of {{convert|319|-|371|mm|in|abbr=on}}, averaging {{convert|339|mm|in|abbr=on}}, in males and {{convert|343|-|388|mm|in|abbr=on}}, averaging {{convert|362.8|mm|in|abbr=on}}, in females.<ref name= Konig/><ref name= Earhart/><ref name= FLMNH>{{cite web| url=http://www.flmnh.ufl.edu/scripts/DBs/birds_pub_proc.asp?output_style=table_type&search_type=1&MaxRecords=50&trys=1&taxon=BUBO-VIRGINIANUS |title=Bird Master Database Search- Bubo virginianus |publisher=Florida Museum of Natural History |access-date=September 23, 2019}}</ref> Unexpectedly, although it is not the longest-winged, the nominate is the heaviest known race as males weigh from {{convert| 985|to|1588|g|lb|abbr=on}}, averaging {{convert|1318|g|lb|abbr=on}}, and females weigh from {{convert|1417|to|2503|g|lb|abbr=on}}, averaging {{convert|1768.5|g|lb|abbr=on}}; the prior figures originally from a huge sample around [[Michigan]]. In comparison, ''B. v. subarcticus'', though averaging longer in wing length averages somewhat less heavy.<ref name= Craighead/><ref name= Earhart/> On the contrary, in [[Costa Rica]], within the range of the possibly synonymous ''mesembrinus'', great horned owls average approximately {{convert|1000|g|lb|abbr=on}}, the lightest average mass reported anywhere for this species.<ref name= Stiles>{{cite book |last1=Stiles |first1=F. G. |first2=A. F. |last2=Skutch |year=1989 |title=A guide to the birds of Costa Rica |publisher=Comstock Publishing Associates, Cornell University Press |location=Ithaca, NY |isbn=0-8014-9600-4}}</ref>  Other standard measurements of this race are a tail length of {{convert|190|to|235|mm|in|abbr=on}}, a tarsus length of about {{convert|56|to|58|mm|in|abbr=on}} and a bill length of {{convert|35|to|50|mm|in|abbr=on}}.<ref name= Konig/><ref name= Craighead/><ref name= Earhart /><ref name= FLMNH/> ''B. v. virginianus'' also tends to have relatively the longest ear tufts on any race.<ref name= Mikkola/>
'''[[South American great horned owl]]''' (''Bubo virginianus nacurutu'')
[[File:Bubo virginianus nacurutu - Otter, Owl, and Wildlife Park.jpg|thumb|upright|[[South American great horned owl]] (''B. v. nacurutu'') with its notably dark eyes]]
:Originally named as a separate species ''Strix nacurutu'', A lowland form occurring in disjunct populations from eastern [[Colombia]] to the [[Guiana Shield|Guyanas]]; also from [[Brazil]] and [[Uruguay]] south of the [[Amazon Basin]] to [[Bolivia]], the [[Buenos Aires Province]] in northern [[Argentina]] and western [[Paraguay]]; resident all-year. Includes the proposed subspecies ''scotinus'', ''elutus'', and ''deserti''.<ref name= Houston/><ref name= Traylor>{{cite journal |last1=Traylor |first1=M. A. |year=1958 |title=Variation in South American Great Horned Owls |journal=The Auk |volume=75 |issue=2 |pages=143–149 |doi=10.2307/4081883 |jstor=4081883 |doi-access=free }}</ref><ref name = holtetal1999>{{cite book |last1=Holt |first1=D. W. |last2=Berkley |first2=R. |last3=Deppe |first3=C. |last4=Enríquez Rocha |first4=P. L. |last5=Olsen |first5=P. D. |last6=Petersen |first6=J. L. |last7=Wood |first7=K. L. |year=1999 |page=69 |chapter=Great Horned Owl |title=Handbook of Birds of the World, Vol 5 |publisher=Lynx Edicions |isbn=978-84-87334-25-2}}</ref> The status of this form, especially the relationships between the scattered subpopulations and with ssp. ''nigrescens'' and the Magellanic horned owl, deserves more study.
:Dull, earthy brownish color is typical; birds from the semiarid interior of Brazil often have much white on uppertail- and ear-coverts against a dull gray background (sometimes separated as ''deserti''). This race is less fuscous than ''nigrescens''. It is the only subspecies where the [[Iris (anatomy)|iris]] is amber, not yellow. The Magellanic horned owl, while somewhat similar in coloring, has yellow eyes like other horned owls, not amber eyes. ''B. v. nacurutu'' is a medium-sized race, smaller than most in North America but not as small as some of the [[Mexico|Mexican]] races. The [[Wing chord (biology)|wing chord]] length is {{convert|330|-|354|mm|in|abbr=on}} in males and {{convert|340|-|376|mm|in|abbr=on}} in females. The tail in both sexes can range from {{convert|184|to|217|mm|in|abbr=on}}. Only three birds have had published weights, two males scaling {{convert|1011|and|1132|g|lb|abbr=on}} and one female weighing {{convert|1050|g|lb|abbr=on}}. The most notable feature of this race is its large bill, at {{convert|43|to|52|mm|in|abbr=on}}, which is the biggest of any horned owl race despite the otherwise moderate size of ''B. v. nacurutu''.<ref name= Mikkola/><ref name= Houston/><ref name= Traylor/>
'''Northern/sub-Arctic great horned owl''' (''Bubo virginianus subarcticus'')
[[File:Horned1b.jpg|thumb|upright|Northern great horned owl (''B. v. subarcticus'') in [[Manitoba]]]]
:Breeding range from [[Mackenzie, British Columbia]] region east to the southern [[Hudson Bay]]; southern limit unclear but at least reaches to [[Montana]] and [[North Dakota]]. Non-breeding birds are regularly found south to [[latitude]] [[45th parallel north|45°S]], i.e. [[Wyoming]] or [[South Dakota]], occasionally ranging beyond this limit especially in years with low prey in the north. This race includes the birds described as ''occidentalis'' (based on a wintering individual, as was the original ''subarcticus'') and ''sclariventris''.<ref>{{cite journal |last1=Dickerman |first1=R. W. |year=1991 |title=On the validity of Bubo virginianus occidentalis (Stone) |journal=The Auk |volume=108 |pages=964–965 |url=https://academic.oup.com/auk/article/108/4/964/5172829 }}</ref> 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]]''.<ref>{{cite journal |last1=Browning |first1=M. R. |first2=R. C. |last2=Banks |year=1990 |title=The identity of Pennant's "Wapacuthu Owl" and the subspecific name of the population of ''Bubo virginianus'' from west of Hudson Bay |journal=Journal of Raptor Research |volume=24 |pages=80–83 |url=https://www.biodiversitylibrary.org/page/51313038#page/6/mode/1up}}</ref> The population described as ''algistus'' is probably based on wandering individuals and/or various intergrades of ''subarcticus'' with other races.<ref name= Houston/><ref>{{cite journal |last1=Dickerman |first1=R. W. |year=1993 |title=The subspecies of the Great Horned Owls of the central great plains, with notes on adjacent areas |journal=Kansas Ornithology Society Bulletin |volume=44 |pages=17–21}}</ref>
:This is the palest form of horned owl, with the ground color essentially whitish with a faint buff tinge above; black underside barring variable from indistinct to pronounced, being most often prominent on the upper chest amongst otherwise pale plumage. This race shows little to no reddish coloration. ''B. v. subarcticus'' shows a very high degree of clinal variation, ranging from in the [[Contiguous United States]] where owls are often medium-grayish and more heavily marked to the [[subarctic]] zone in Canada where very pale birds with almost non-existent markings are prominent. Very pale birds are similar to a young female snowy owl from a distance. In this race, the feet range from immaculate white to buff, with little or no mottling.<ref name= Konig/><ref name= Houston/> In the west of Canada, ''subarcticus'' may hybridize with the dark ''saturatus'' and may do the same with this similarly dark ''heterocnemis'' in the east. In both cases, they may produce intermediate looking hybrids of reddish tone, like a ''virginianus'' but with sharper contrasting of colors.<ref name= Taverner>{{cite journal |last1=Taverner |first1=P. A. |year=1942 |title=Canadian Races of the Great Horned Owls |journal=The Auk |volume=59 |issue=2 |pages=234–245 |doi=10.2307/4079554|jstor=4079554 }}</ref> This is one of the largest-bodied subspecies.<ref>{{cite book|last=Bendire|first=Charles|url=https://books.google.com/books?id=x5fnAAAAMAAJ&q=bubo+virginianus+subarcticus+largest&pg=PA383 |title=Smithsonian Contributions to Knowledge: Life Histories of North American Birds |publisher=The Smithsonian Institution |year=1892 |access-date=2012-02-09|page=383}}</ref> The [[Wing chord (biology)|wing chord]] length is {{convert|323|-|372|mm|in|abbr=on}}, averaging {{convert|346.7|mm|in|abbr=on}}, in males and {{convert|339|-|390|mm|in|abbr=on}}, averaging {{convert|362.5|mm|in|abbr=on}}, in females. Body mass ranges from {{convert|865|to|1460|g|lb|abbr=on}}, averaging {{convert|1196.5|g|lb|abbr=on}}, in males and from {{convert|1112|to|2046|g|lb|abbr=on}}, averaging {{convert|1556|g|lb|abbr=on}}, in females. Tail length is {{convert|200|to|225|mm|in|abbr=on}} and {{convert|220|to|240|mm|in|abbr=on}} in males and females, respectively. Bill length is {{convert|35|to|43|mm|in|abbr=on}} in both and one bird had a tarsus of {{convert|66|mm|in|abbr=on}}.<ref name= Voous/><ref name= Mcgillivray /><ref name= Snyder/><ref name= Earhart/><ref>{{cite book |last1=Godfrey |first1=W. E. |year=1986 |title=The birds of Canada |edition=Revised |publisher=National Museum of Natural Sciences |location=Ottawa |asin=B003XVMPTC}}</ref><ref>{{cite journal |last1=Snyder |first1=L. L. |year=1961 |title=On an unnamed population of the Great Horned Owl |journal=Ontario Museum, Contribution |volume=54 |url=https://www.biodiversitylibrary.org/item/111762#page/7/mode/1up}}</ref>
'''California great horned owl''' (''Bubo virginianus pacificus'')
[[File:Great-horned-owl-stretching.jpg|thumb|right|California great horned owl (''B. v. pacificus'') stretching, Bernal Hill Park, [[San Francisco]]]]
:Central and southern California west of the [[Sierra Nevada (U.S.)|Sierra Nevada]] except for the [[San Joaquin Valley]], south to Northwestern [[Baja California]], [[Mexico]]. Intergrades with ''pallescens'' in [[San Diego County]], California (see also below). Resident all-year.<ref name= Houston/>
:Very rich brown, dark underside barring distinct, less pronounced than in ''saturatus'' but more pronounced than in ''pallescens''. [[Humerus|Humeral]] area is black. Feet are mottled dark. The facial disc is often even darkly mottled.<ref name= Houston/> This is a fairly small-bodied race, in fact including the lightest wild great horned owl adult ever weighed. The [[Wing chord (biology)|wing chord]] length is {{convert|305|-|362|mm|in|abbr=on}}, averaging {{convert|332.5|mm|in|abbr=on}}, in males and {{convert|335|-|375|mm|in|abbr=on}}, averaging {{convert|351.4|mm|in|abbr=on}}, in females. Body mass ranges from {{convert|680|to|1272|g|lb|abbr=on}}, averaging {{convert|991.7|g|lb|abbr=on}}, in males and from {{convert|825|to|1668|g|lb|abbr=on}}, averaging {{convert|1312.7|g|lb|abbr=on}}, in females. Tail length is {{convert|175|to|218|mm|in|abbr=on}} and {{convert|203|to|230|mm|in|abbr=on}} in males and females, respectively. Bill length is {{convert|34|to|41|mm|in|abbr=on}} and one bird had a tarsus of {{convert|57|mm|in|abbr=on}}.<ref name= Voous/><ref name= Mcgillivray/><ref name= Snyder/><ref name= Earhart/>
'''Coastal great horned owl''' (''Bubo virginianus saturatus'')
[[File:Great Horned Owl.jpg|thumb|right|Coastal great horned owl (''B. v. saturatus'') at [[Grouse Mountain]] ([[North Vancouver (district municipality)|North Vancouver]], [[British Columbia]])]]
:[[Pacific]] coast from southeastern [[Alaska]] to northern California. Includes the previously described form of  ''B. v. leucomelas''. The often-recognized race ''B. v. lagophonus'' is often now considered a mere clinal variation of the same race from interior [[Alaska]] to [[Oregon]], the [[Snake River]], and northwestern [[Montana]].<ref name= Houston/><ref name= Taverner/> These forms may be reported in winter as far south as [[Colorado]] and [[Texas]], but these are in times of [[irruption]].<ref name="holtetal1999" />
:A dark and overall brownish form with heavily barred and mottled underside, with a dull tawny base. Inland birds (''lagophonus'') tend to have a more grayish base, the coastal owls being more richly brown. Otherwise, inland and coastal owls are practically the same. The facial disc can range from gray to reddish-gray to dark rufous. The feet are fairly dusky gray typically, although some buff-footed individuals are known, and legs are more prominently barred with black than in other North American races.<ref name= Konig/><ref name= Houston/> This is a large race going on linear measurements, which in [[Alaska]]n owls outmatch those of all other races but for ''heterocnemis'' in [[Ontario]] (which may itself be a discontinuous eastern wing of this race). The [[Wing chord (biology)|wing chord]] length is {{convert|330|-|370|mm|in|abbr=on}}, averaging {{convert|348.3|mm|in|abbr=on}}, in males and {{convert|339|-|400|mm|in|abbr=on}}, averaging {{convert|374.7|mm|in|abbr=on}}, in females. Tail length is {{convert|191|to|245|mm|in|abbr=on}} and {{convert|196|to|252|mm|in|abbr=on}} in males and females. In both sexes, known bill and tarsal lengths are {{convert|35|to|44|mm|in|abbr=on}} and {{convert|62|to|70|mm|in|abbr=on}}. No weights are known to have been published.<ref name= Voous/><ref name= Mcgillivray/><ref name= Snyder/><ref name= Earhart/>
'''North Andean great horned owl''' (''Bubo virginianus nigrescens'')
:[[Andes]]; arid [[temperate]] and [[Puna grassland|puna]] zones from [[Colombia]] to northwestern [[Peru]]. Resident all-year round. Presumably synonymous with the described ''columbianus''.<ref name= Konig/>
:A dark, cold gray-brown form with heavy fuscous blotching. Arguably this is the darkest colored race on average, though it could be rivaled by individuals from ''saturatus'' and ''elachistus''. This race has only minimally the rufous tinge seen in other darkish races, although some ''nigrescens'' may have a cinnamon facial disc.<ref name= Konig/> The largest winged race of owl in South America, this owl has a [[Wing chord (biology)|wing chord]] length of {{convert|345|-|365|mm|in|abbr=on}} in males and {{convert|350|-|382|mm|in|abbr=on}} in females. The tail in both sexes can range from {{convert|185|to|217|mm|in|abbr=on}}. Bill length is {{convert|40|to|50|mm|in|abbr=on}}, again relatively long as in ''nacurutu'' and one bird had a tarsal length of {{convert|80|mm|in|abbr=on}}, indicating relatively long legs in the race. No published weights are known.<ref name= Voous/><ref name= Traylor/> Apparently, despite its sizeable wing area, ''nigrescens'' is notably smaller overall when specimens are compared side-by-side with those from ''saturatus''.<ref name= Konig/>
'''Desert great horned owl''' (''Bubo virginianus pallescens'')
[[File:Great Horned Owl in a Rain Storm in the Mojave.jpg|thumb|right|Desert great horned owl (wet feathered) (''B. v. pallescens'') waiting out a rainstorm in the [[Mojave Desert]]]]
[[File:Great Horned Owl Sleeping.jpg|thumb|right|[[Mojave Desert]], desert great horned owl (''B. v. pallescens'') on top of a Joshua tree in the summer of 2018]]
:[[San Joaquin Valley]] southeastwards through arid regions of southeastern California and southern [[Utah]] eastwards to western [[Kansas]] and southwards to [[Guerrero]] and western [[Veracruz]] in [[Mexico]]; intergrades with ''pacificus'' in [[San Diego County]], if not elsewhere; vagrant individuals of ''saturatus'' and the [[Rocky Mountains]] population, which look similar to intergrades, also seem to occur in its range. Resident all-year.<ref name= Houston/> This race is likely synonymous with ''melanocercus''.<ref name= Konig/>
:A pale dusky buff form with indistinct barring, especially on the underside. Darker individuals tend to have a deeper [[fulvous]] base to their upper sides. Humeral area is umber in color and the feathers of the feet are white and usually unmarked.<ref name= Konig/> A small race, it averages slightly larger in wing length than ''pacificus'' but weighs less on average. The [[Wing chord (biology)|wing chord]] length is {{convert|318|-|367|mm|in|abbr=on}}, averaging {{convert|337.2|mm|in|abbr=on}}, in males and {{convert|332|-|381|mm|in|abbr=on}}, averaging {{convert|348.9|mm|in|abbr=on}}, in females. Body mass ranges from {{convert|724|to|1257|g|lb|abbr=on}}, averaging {{convert|914.2|g|lb|abbr=on}}, in males and from {{convert|801|to|1550|g|lb|abbr=on}}, averaging {{convert|1142.2|g|lb|abbr=on}}, in females. In both sexes, tail length is {{convert|190|to|235|mm|in|abbr=on}} and bill length is {{convert|33|to|43|mm|in|abbr=on}}.<ref name= Voous/><ref name= Mcgillivray/><ref name= Snyder/><ref name= Earhart/>
'''Yucatán great horned owl''' (''Bubo virginianus mayensis'')
:Endemic to the southern two-thirds of the [[Yucatán Peninsula]]. Resident all-year.
:A medium-pale form, fairly similar to ''pallescens'' in both hue and ventral markings. Going on linear measurements, ''B. v. mayensis'' is smaller than all North American horned owls, even the smallish ''pallescens'', and is only slightly larger at median than the following race.<ref name= Voous/> This race has [[Wing chord (biology)|wing chord]] and tail lengths of {{convert|297|-|340|mm|in|abbr=on}} and {{convert|180|to|198|mm|in|abbr=on}} in males and {{convert|303|-|357|mm|in|abbr=on}} and {{convert|199|to|210|mm|in|abbr=on}} in females. In both sexes, the bill length is {{convert|39|to|41|mm|in|abbr=on}} and tarsal length is {{convert|54|to|65|mm|in|abbr=on}}.<ref name= Webster/>
'''Baja California great horned owl''' (''Bubo virginianus elachistus'') 
:Southern [[Baja California]], [[Mexico]]. Resident all-year.
:Similar in color to ''pacificus'' but even darker and more heavily barred, like a miniaturized ''saturatus''. It is considerably (5–10%) smaller than ''pacificus'' linearly; some size overlap does occur though. On average, it is the smallest known subspecies. Males have a wing chord length of {{convert|305|to|335|mm|in|abbr=on}}, tail length of {{convert|175|to|206|mm|in|abbr=on}} and bill length of {{convert|33|to|38|mm|in|abbr=on}}. A single female had a wing chord of {{convert|330|mm|in|abbr=on}} and tail of {{convert|211|mm|in|abbr=on}}.<ref name=Konig/><ref name= Webster/>
'''Northeastern great horned owl''' (''Bubo virginianus heterocnemis'')
:Breeds in eastern Canada (northern [[Quebec]], [[Labrador]], [[Newfoundland (island)|Newfoundland]]). Its southern breeding range seems to be delineated by the [[Saint Lawrence River]].<ref name= Taverner/>  In winter, this race may disperses southwards throughout [[Ontario]] to as far as the [[Northeastern United States]]. This subspecies may be synonymous with ''saturatus'', although it is distributed far to the east of that race. ''B. v. heterocnemis'' is surrounded by the much paler ''subarcticus'' to its west and quite differently marked ''virginianus'' to its south, the latter two overlap and possibly hybridize in some of the northeast.<ref name="holtetal1999" />
:A fairly dark and grey, heavily barred form. Feet pale with dusky mottling. Going on median reported linear measurements (since body mass is unknown), this is the largest bodied subspecies on average. Males have a wing chord length of {{convert|350|to|365|mm|in|abbr=on}} and females range from {{convert|370|to|390|mm|in|abbr=on}}. In both sexes, the tail is {{convert|220|to|250|mm|in|abbr=on}} and the bill is {{convert|38|to|48|mm|in|abbr=on}}.<ref name= Voous/><ref name= Houston/><ref name= Taverner/>
'''Rocky Mountains great horned owl''' (''Bubo virginianus pinorum'')
:The [[Rocky Mountains]] population breeds south of the [[Snake River]] in [[Idaho]] south to [[Arizona]], [[New Mexico]], and the [[Guadalupe Mountains]] of [[Texas]]. Westwards, it is presumed to occur to the [[Modoc Plateau]] and [[Mono Lake]] of California. This race was included in the presumed subspecies ''occidentalis'', but was recently first described and named as a distinct subspecies and makes up the missing piece in the once-muddled distribution of great horned owls in the West and Rockies. Downslope movements into valleys occupied by ''pallescens'' might occur, but this needs study.
:A medium gray form, intermediate in coloring between ''saturatus'' and ''pallescens''. Moderately barred and tinged buff or ochraceous on the underside. Feet mottled. This is a largish race, wing chord lengths being inexplicably greater in males, at {{convert|350|to|397|mm|in|abbr=on}}, than in females, at {{convert|327|to|367|mm|in|abbr=on}}. Tail length can range from {{convert|190|to|233|mm|in|abbr=on}} and a female weighed {{convert|1246|g|lb|abbr=on}}.<ref name= Houston/><ref>{{cite journal |last1=Dickerman |first1=R. W. |last2=Johnson |first2=A. B. |year=2008 |title=Notes on Great Horned Owls nesting in the Rocky Mountains, with a description of a new subspecies |journal=Journal of Raptor Research |volume=42 |issue=1 |pages=20–28 |doi=10.3356/JRR-06-75.1|s2cid=84498763 |doi-access=free }}</ref>

===Species identification===
[[File:PSM V41 D334 Great horned and snowdon owls.jpg|thumb|right|Illustrated comparison of a great horned owl, left, to its closest North American relative, the snowy owl]]
The combination of the species' bulk, prominent ear tufts and barred plumage distinguishes it through much of the range, but it may be easily confused with the [[lesser horned owl]] (''B. magellanicus''), which may overlap in range.<ref name= Konig/> The Magellanic horned owl was once considered a subspecies of the great horned, but is now almost universally considered a distinct species, as is supported by genetic materials, with the great horned being the [[paraspecies]].<ref name= Konig/><ref name= Mikkola/> Overall coloration is similar, but the Magellanic is markedly smaller with smaller feet and a smaller head, with finer, but more numerous brownish bars on the underside, rather than the blotchy, irregular barring typical of great horned owls.<ref name=Konig/> Other [[eagle-owl]]s may superficially be somewhat similar, but the species is generically [[allopatric]] with the exception of wintering snowy owls. More tropical species with ear tufts, the [[stygian owl]] (''A. stygius'') and [[striped owl]] (''A. clamator''), are much smaller.<ref name= Konig/> Other large owls lack ear tufts.<ref name= Voous/>

==Distribution and habitat==
[[File:Great Horned Owl, Ontario, Canada.jpg|thumb|A great horned owl in a barn, Ontario, Canada]]
[[File:Great Horned owl flying from a barn, Southern Ontario 386.jpg|thumb|The same owl in flight]]

The breeding habitat of the great horned owl extends high into the [[subarctic]] of North America, where they are found up to the northwestern and southern [[Mackenzie Mountains]], [[Keewatin, Ontario]], northern [[Manitoba]], [[Fort Chimo]] in [[Ungava Peninsula|Ungava]], [[Okak, Newfoundland and Labrador]], [[Anticosti Island]] and [[Prince Edward Island]]. They are distributed throughout most of North America and very spottily in Central America and then down into South America south to upland regions of [[Argentina]], [[Bolivia]] and [[Peru]], before they give way to the Magellanic horned owl, which thence ranges all the way to [[Tierra del Fuego]], the southern tip of the continent. It is absent or rare from southern [[Guatemala]], [[El Salvador]], [[Nicaragua]], and [[Costa Rica]] to [[Panama]] (where only two records) in Central America and the mangrove forests of northwestern South America. The species is also absent from the [[West Indies]], the [[Haida Gwaii]] and almost all off-shore islands in the Americas, its ability to colonize islands apparently being considerably less than those of barn owls and [[short-eared owl]]s.<ref name= Voous/><ref name= Stiles/><ref name="holtetal1999" /><ref>{{cite book |last1=Howell |first1=S. N. G. |first2=S. |last2=Webb |year=1995 |title=A guide to the birds of Mexico and northern Central America |publisher=Oxford Univ. Press |location=New York |isbn=0-19-854012-4}}</ref><ref>{{cite book |last1=Ridgely |first1=R. S. | first2=J. A. Jr. | last2=Gwynne |year=1989 |title=A guide to the birds of Panama |edition=2 |publisher=Princeton Univ. Press |location=Princeton, NJ |isbn=978-0-691-02512-4}}</ref> Since the division into two species, the great horned owl is the second most widely distributed owl in the Americas, just after the barn owl.<ref name=Konig/>

[[File:Great Horned Owl at twilight, Mojave Desert.jpg|thumb|right|Desert great horned owl (''B. v. pallescens'') perched on the top of a Joshua tree in [[Landers, California]]]]

The great horned owl is among the world's most adaptable owls or even bird species in terms of habitat. The great horned owl can take up residence in trees that border all manner of [[deciduous]], [[coniferous]], and [[mixed forest|mixed]] forests, [[tropical rainforest]]s, [[pampa]]s, [[prairie]], mountainous areas, [[desert]]s, subarctic [[tundra]], rocky coasts, [[mangrove swamp]] forests, and some [[urban area]]s.<ref name=Konig/> It is less common in the more extreme areas of the Americas. In the [[Mojave Desert|Mojave]] and [[Sonora Desert]]s, they are absent from the heart of the deserts and are only found on the vegetated or rocky fringes. Even in North America, they are rare in landscapes including more than 70% old-growth forest, such as the [[aspen]] forest of the Rockies.<ref name= Houston/><ref>{{cite journal |last1=Flack |first1=J.A.O. |year=1976 |title=Bird populations of aspen forests in Western North America |journal=Ornithological Monographs |issue=19 |pages=1–97 |doi=10.2307/40166754|jstor=40166754 |url=https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=6022&context=aspen_bib |url-access=subscription }}</ref> They have only been recorded a handful of times in true [[rainforest]]s such as the [[Amazon rainforest]].<ref name= Voous/> In the [[Appalachian Mountains]], they appear to use old-growth forest<ref>{{cite journal |last1=Mcgarigal |first1=K. |first2=J. D. |last2=Fraser |year=1984 |title=The effect of forest stand age on owl distribution in southwestern Virginia |journal=Journal of Wildlife Management |volume=48 |issue=4 |pages=1393–1398 |doi=10.2307/3801804|jstor=3801804 }}</ref> but in [[Arkansas]] are often found near temporary agricultural openings in the midst of large areas of woodland.<ref>{{cite book |last1=James |first1=D. A. |first2=J. C. |last2=Neal |year=1986 |title=Arkansas birds: their distribution and abundance |publisher=University of Arkansas Press |location=Fayetteville |isbn=0-938626-38-8}}</ref> Similarly in south-central [[Pennsylvania]], the owls use cropland and pasture more than deciduous and total forest cover, indicating preference for fragmented landscapes.<ref>{{cite journal |last1=Morrell |first1=T. E. |first2=R. H. |last2=Yahner |year=1994 |title=Habitat characteristics of Great Horned Owls in southcentral Pennsylvania |journal=Journal of Raptor Research |issue=28 |pages=164–170 |url=https://archive.org/details/biostor-215685}}</ref> 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 shelter and nesting sites.<ref name= Voous/><ref name= Smith>{{cite journal |last1=Smith |first1=D. G. |first2=J. R. |last2=Murphy |year=1982 |title=Nest site selection in raptor communities of the Eastern Great Basin Desert |journal=Great Basin Naturalist |volume=42 |issue=3 |pages=395–404 |jstor=41711942}}</ref>

In mountainous areas of North America, they are usually absent above the [[tree line]], but great horned owls can be found up to {{convert|2100|m|ft|abbr=on}} in California and {{convert|3300|m|ft|abbr=on}} in the Rockies.<ref name= Voous/><ref>{{cite book |last1=Root |first1=T. |year=1988 |title=Atlas of wintering North American birds: an analysis of Christmas bird count data |publisher=University of Chicago Press |location=Chicago |isbn=978-0-226-72540-6}}</ref> In the Andean Mountains,  on the other hand, they have adapted to being a true montane species, often found at least {{convert|3300|m|ft|abbr=on}} above sea level and are regularly recorded in treeless [[Puna grassland]] zones at {{convert|4100|to|4500|m|ft|abbr=on}} in [[Ecuador]] and [[Peru]].<ref>{{cite book |last1=Fjeldså |first1=J. |first2=N. |last2=Krabbe |year=1990 |title=Birds of the high Andes |publisher=Zoological Museum, University of Copenhagen, and Apollo Books |location=Svendborg, Denmark |isbn=87-88757-16-1}}</ref> They are generally rare in non-tidal wetland habitat<ref>{{cite journal |last1=Accordi |first1=I. A. |last2=Barcellos |first2=A. |year=2006 |title=Composição da avifauna em oito áreas úmidas da Bacia Hidrográfica do Lago Guaíba, Rio Grande do Sul |journal=Revista Brasileira de Ornitologia |volume=14 |issue=2 |pages=101–115 |url=https://www.academia.edu/22682003}}</ref> and are replaced in the high [[Arctic tundra]] by snowy owls.<ref name=Konig/> They prefer areas where open habitats, which they often hunt in, and woods, where they tend to roost and nest, are juxtaposed.<ref name= Johnson2/><ref name= Rohner2>{{cite journal |last1=Rohner |first1=C. |first2=C. J. |last2=Krebs |year=1996 |title=Owl predation on snowshoe hares: consequences of antipredator behaviour |journal=Oecologia |volume=108 |issue=2 |pages=303–310 |doi=10.1007/BF00334655 |jstor=4221419|pmid=28307843 |bibcode=1996Oecol.108..303R |s2cid=8013050 }}</ref><ref>{{cite journal |last1=Ganey |first1=J. L. |last2=Vojta |first2=S. C. |year=2005 |title=Changes in snag populations in northern Arizona mixed-conifer and ponderosa pine forests, 1997–2002 |journal=Forest Science |volume=51 |issue=5 |pages=396–405 |doi=10.1093/forestscience/51.5.396 |url=https://research.fs.usda.gov/treesearch/23997}}</ref> Thus lightly populated rural regions can be ideal. This species can occasionally be found in urban or suburban areas. However, they seem to prefer areas with less human activity and are most likely to be found in park-like settings in such developed areas, unlike [[Eastern screech owl|eastern]] and [[western screech owl]]s (''Megascops asio'' & ''M. kennicottii'') which may regularly occur in busy suburban settings. 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.<ref name=Konig/>

==Behavior==
[[File:Great-horned-owl-in-flight.jpg|thumb|left|Composite photo of great horned owl flight phases]]
[[File:Bubo virginianus (Grand-duc d'Amérique).jpg|thumb|right|upright|Great horned owls are typically sluggish and passive but aware during daytime.]]
In most aspects of their behavior, great horned owls are typical of owls and most birds of prey. Like most owls, the great horned owl makes great use of secrecy and stealth. Due to its natural-colored plumage, it is well camouflaged both while active at night and while roosting during the day. During the daytime it roosts usually in large trees (including snags and large hollows but usually thick branches) but may occasionally be in crevices or small caves in rocks or in dense shrubbery. [[Pine]] and other [[Pinophyta|coniferous trees]] may be preferred where available since they are particularly dense and provide cover throughout the year. Typically, males have a favorite roosting site not far from the nest, sometimes used over successive years.<ref name="Austing" /> While roosting, great horned owls may rest in the "tall-thin" position, where they sit as erect and hold themselves as slim as is possible. The kind of posture is well known as a further method of camouflage for other owls, like long-eared owls or great grey owls, especially if humans or other potential mammalian carnivores approach them.<ref name="Hume">{{cite book |last1=Hume, R. |year=1991 |title=Owls of the world |publisher=Running Press |location=Philadelphia, PA |isbn= 1-56138-032-6}}</ref>

Outside of the nesting season, great horned owls may roost wherever their foraging path ends at dawn.<ref name="Rohner" /> Generally great horned owls are active at night, although in some areas they may be active in the late afternoon or early morning. At dusk, the owl utters a few calls before flying to a more open sing-post, i.e. large bare branch or large rocks to deliver song. Normally several perches are used to mark occupied territory or to attract a female.<ref name="Konig" /> Despite its camouflage and cryptic locations, this species can still sometimes be spotted on its daytime roosts, especially by [[American crow]]s (''Corvus brachyrhynchos''). Since owls are, next to [[red-tailed hawk]]s, perhaps the main predator of crows and their young, crows sometimes congregate from considerable distances to mob owls and caw angrily at them for hours on end.<ref>{{Cite web |title=Great Horned Owl Overview, All About Birds, Cornell Lab of Ornithology |url=https://www.allaboutbirds.org/guide/Great_Horned_Owl/overview |access-date=2024-05-12 |website=www.allaboutbirds.org |language=en}}</ref> When the owls try to fly off to avoid this harassment, they are often followed by the corvids.<ref>{{cite web | url=http://wesleytheowl.blogspot.ca/2010/04/crows-and-ravens-corvids-and-their-odd.html | title=Stacey O'Brien: Wesley the Owl: Crows and Ravens: The Corvids and their odd behavior| date=2010-04-13}}</ref>

===Territoriality and movements===
Typically, great horned owls are highly sedentary, often capable of utilizing a single territory throughout their mature lives.<ref>{{cite journal |last1=Baumgartner |first1=F. M. |year=1939 |title=Territory and population in the Great Horned Owl |journal=The Auk |volume=56 |issue=3 |pages=274–282 |doi=10.2307/4079048|jstor=4079048 |doi-access=free }}</ref> Although some species such as snowy owls, [[northern saw-whet owl]]s, [[long-eared owl|long-eared]] and short-eared owls are true migrants, most North American owls are not migratory and will generally show fidelity to a single territory year around.<ref name= Voous/> In great horned owls, mated pairs occupy territories year-round and long-term. Territories are established and maintained through hooting, with highest activity before egg-laying and second peak in autumn when juveniles disperse, and can range from an average of {{convert|16 |km2|sqmi|abbr=on}} in [[Yukon]] to an average of {{convert|2.1 |km2|sqmi|abbr=on}} in [[Wyoming]].<ref name= Craighead/><ref name= Rohner/>

Most territorial defense is performed by males, but females frequently assist their partners in hooting contests with neighbors or intruders, even during incubation.<ref name= Houston/> On occasion, although territory borders may be successfully maintained via vocalizations alone without even seeing the competing owl, such confrontations may turn physical, with various levels of threats distinguished. 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. If the intruder continues to press the confrontation, the defending owl will "hop" forward and strike it with feet, attempting to grasp and rake with claws.<ref name= Houston/>

Territoriality appears to place a limit on the number of breeding pairs in a given area. Individuals prevented from establishing a territory live a silent existence as "floaters". Radio-telemetry revealed that such floaters concentrate along boundaries of established territories. At [[Kluane Lake]] in [[Yukon]], incursions into neighboring territories were observed only twice—by females when a neighboring female had died or emigrated, suggesting that territorial defense may be sex-specific. At least four dead great horned owls in Kluane were apparently killed by others of their own species in territorial conflicts.<ref name= Rohner/> Owls killed by other horned owls are sometimes cannibalized, although the origin of the killing may have been territorial aggression.<ref>{{cite journal |last1=Millard |first1=J. B. |first2=T. H. |last2=Craig |first3=O. D. |last3=Markham |year=1978 |title=Cannibalism by an adult Great Horned Owl |journal=Wilson Bulletin |volume=90 |issue=3 |page=449 |url=https://sora.unm.edu/node/129540}}</ref> Northern populations occasionally irrupt south during times of food shortage,<ref name= Houston2>{{cite journal | last1=Houston |first1=C. S. |year=1978 |title=Recoveries of Saskatchewan-banded Great Horned Owls |journal=Canadian Field-Naturalist |volume=92 |pages=61–66|doi=10.5962/p.346633 |doi-access=free }}</ref> but there is no annual migration even at the northern limits of the great horned owl's range.<ref name= Rohner/>

===Hunting behavior===
[[File:0 Bubo virginianus - Grand-duc d'Amérique (1).JPG|thumb|right|His piercing yellow eyes and his ear tufts.]]
[[File:Claws1a.jpg|thumb|right|Closeup of great horned owl toes and talons]]
Hunting tends to peak between 8:30 pm and midnight and then can resume from 4:30 am to sunrise.<ref name= Smith2>{{cite journal |last1=Smith |first1=D. G. |first2=J. R. |last2=Murphy |year=1973 |title=Breeding ecology of raptors in the eastern Great Basin of Utah |journal=Brigham Young University Science Bulletin Biological Services |volume=18 |issue=3 |pages=1–76 |url=https://scholarsarchive.byu.edu/byuscib/vol18/iss3/1}}</ref> Hunting tends to be most prolonged during winter by virtue of prey being more scarce.<ref>{{cite thesis |last1=Fuller |first1=M. R. |year=1979 |title=Spatiotemporal ecology of four sympatric raptor species |type=Ph.D. |publisher=Univ. of Minnesota |location=St. Paul}}</ref>  However, great horned owls can learn to target certain prey during daylight in the afternoon when it is more vulnerable, such as [[Fox squirrel|eastern fox squirrels]] (''Sciurus niger'') while they are building their leaf nests and [[Sauromalus ater|chuckawallas]] (''Sauromalus ater'') sunning themselves on desert rocks.<ref>{{cite journal |last1=Packard |first1=R. L. |year=1954 |title=Great horned owl attacking squirrel nests |journal=The Wilson Bulletin |volume=66 |issue=4 |page=272 |url=https://sora.unm.edu/sites/default/files/journals/wilson/v066n04/p0272-p0272.pdf}}</ref><ref>{{cite journal |last1=Vaughan |first1=T.A. |year=1954 |title=Diurnal foraging by the Great Horned Owl |journal=Wilson Bulletin |volume=66 |issue=2 |page=148 |jstor=4158310}}</ref> Owls hunt mainly by watching from a snag, pole or other high perch. During hunting forays, they often fly about {{convert|50|to|100|m|ft|abbr=on}} from perch to perch, stopping to survey for food at each, until they sense a prey item below. From such vantage points, owls dive down to the ground, often with wings folded, to ambush their prey.<ref name=Konig/> Effective maximum hunting distance of an owl from an elevated perch is {{convert|90|m|ft|abbr=on}}.<ref name= Petersen/> Due to their short but broad wings, great horned owls are ideally suited for low speed and maneuverability.<ref name= Johnson/>

Despite reports that they do not hunt on the wing,<ref name="Rudolph">{{cite journal |last1=Rudolph |first1=S. G. |year=1978 |title=Predation Ecology of Coexistng Great Horned and Barn Owls |journal=The Wilson Bulletin |volume=90 |issue=1 |pages=134–137 |url=https://sora.unm.edu/sites/default/files/journals/wilson/v090n01/p0134-p0137.pdf}}</ref> they also sometimes hunt by flying low over openings on the ground, scanning below for prey activity.<ref name="Konig" /> Great horned owls can fly at speeds of more than {{convert|65|km/h|mph|abbr=on}} in level flight.<ref name="Voous" /> Hunting flights are slow, often quartering low above the ground where prey is likely to occur in open country or open woodland. Brief hovering flight (for about 6–18 seconds) has been described, especially in windy areas.<ref>{{cite journal |last1=Smith |first1=D. G. |first2=B. A. |last2=Smith |year=1972 |title=Hunting methods and success of newly-fledged Great Horned Owls |journal=Bird-Banding |volume=43 |issue=2 |page=142 |doi=10.2307/4511863 |jstor=4511863 |url=https://sora.unm.edu/node/50297|url-access=subscription }}</ref> On occasion owls may actually walk on the ground in pursuit of small prey or, rarely, inside a chicken coop to prey on the fowl within.<ref name="owlpages.com" /> [[Rodent]]s and [[invertebrate]]s may be caught on foot around the base of bushes, through grassy areas, and near culverts and other human structures in range and farm habitat.<ref name="Houston" /> The great horned owl is generally a poor walker on the ground; it walks like a [[starling]], with a pronounced side-to-side gait. They have been known to wade into shallow water for aquatic prey, although this has been only rarely reported.<ref name="Houston" /> Owls can snatch [[bird]]s and some arboreal mammals directly from tree branches in a glide as well. The stiff feathering of their wings allows owls to produce minimal sound in flight while hunting.<ref name="Cornell" /><ref name="Konig" /><ref name="owlpages.com" />

Almost all prey are killed by crushing with the owl's feet or by incidentally stabbing of the talons, though some may be bitten about the face as well. Prey is swallowed whole when possible. When prey is swallowed whole, owls regurgitate [[Pellet (ornithology)|pellets]] of bone and other non-digestible bits about 6 to 10 hours later, usually in the same location where the prey was consumed.<ref name="Konig" /> Great horned owl pellets are dark gray or brown in color and very large, {{convert|7.6|to|10.2|cm|in|abbr=on}} long and {{convert|3.8|cm|in|abbr=on}} thick, and have been known to contain skulls up to {{convert|3|cm|in|abbr=on}} in width inside them.<ref name="owlpages.com" /> However, not all prey can be swallowed at once, and owls will also fly with prey to a perch and tear off pieces with their bill. Most dietary studies focus on pellets found under perches and around nests, since they provide a more complete picture of the diversity of prey consumed, but prey remains outside of pellets may provide clues to prey excluded from the pellets and a combination of both is recommended.<ref name="Voous" /><ref name="Hamerstrom" /><ref name="Orians">{{cite journal |last1=Orians |first1=G. |last2=Kuhlman |first2=F. |year=1956 |title=Red-tailed hawk and horned owl populations in Wisconsin |journal=The Condor |volume=58 |issue=5 |pages=371–385 |doi=10.2307/1365056|jstor=1365056 }}</ref>

Many large prey items are dismembered. Great horned owls may behead large prey before taking it to its nest or eating perch. The legs may also be removed, as may (in some bird prey) the wings. The great horned owl will also crush the bones of its prey to make it more compact for carrying.<ref>{{cite journal |last1=Einarsen |first1=A. S. |year=1956 |title=Determination of some predator species by food signs |journal=Oregon State Monographs |volume=10 |page=34}}</ref> On occasion, the owls may return to the kill site to continue eating if the prey is too heavy to fly with after dismemberment.<ref name="Bent" /> Many owls will accrue a cache of prey, especially those who are nesting. Caches must be at a safe location, usually the crotch of a tall tree. In northern regions, where large prey is prevalent, an owl may let uneaten food freeze and then thaw it out later using its own body heat.<ref name="Mikkola" />  Hunting success seems to require fairly open understory, and experimental testing of microhabitat proved that open areas provided more hunting success on five species of rodent, with cloudy nights and denser bush foliage both decreasing success.<ref>{{cite journal |last1=Longland |first1=W. S. |first2=M. V. |last2=Price |year=1991 |title=Direct observations of owls and heteromyid rodents: can predation risk explain microhabitat use? |journal=Ecology |volume=72 |issue=6 |pages=2261–2273 |doi=10.2307/1941576|jstor=1941576 |bibcode=1991Ecol...72.2261L }}</ref>

==Prey and trophic ecology==
 [[File:Bubo virginianusDO1908P01CA.JPG|thumb|right|upright|Painting by [[Louis Agassiz Fuertes]] depicting a great horned owl with one of its primary prey species, a [[snowshoe hare]]]]

Prey can vary greatly based on opportunity. According to one author, "Almost any living creature that walks, crawls, flies, or swims, except the large mammals, is the great horned owl's legitimate prey".<ref name=Lubbock/> In fact, the great horned owl has the most diverse prey profile of any raptor in the Americas.<ref name= Voous/> Over 500 species have been identified as great horned owl prey, with dozens more identified only to genus or general type (especially numerous [[invertebrate]]s) and presumably several more unknown from their relatively little-studied populations in the [[Neotropical realm|Neotropic]]s. [[Mammal]]s (more than 200 species) and [[bird]]s (nearly 300 species) make up the majority of their diet.<ref name= Voous/><ref name= Hamerstrom>{{cite journal |last1=Errington |first1=P. L. |first2=F. |last2=Hamerstrom |first3=F. N. Jr. |last3=Hamerstrom |year=1940 |title=The Great Horned Owl and its prey in north-central United States |journal=Iowa Agricultural Express Research Bulletin |volume=24 |issue=277 |pages=757–850 |url=https://dr.lib.iastate.edu/handle/20.500.12876/103885}}</ref> Their diet in North America is made up of 87.6% mammals, 6.1% birds, 1.6% [[reptile]]s and [[amphibian]]s with the remaining 4.7% being made up by insects, other assorted [[invertebrate]]s and [[fish]].<ref name= Voous/>

Estimated mass of individual prey for the owls has ranged from as little as {{convert|0.4|g|oz|abbr=on}} to as much as {{convert|6.8|kg|lb|abbr=on}}<ref name="Cromrich">{{cite journal |last1=Cromrich |first1=L. A. |last2=Holt |first2=D. W. |last3=Leasure |first3=S. M. |year=2002 |title=Trophic niche of North American great horned owls |journal=Journal of Raptor Research |volume=36 |issue=1 |pages=58–65 |url=https://biostor.org/reference/216176}}</ref><ref name="Murphy">{{cite journal |last1=Murphy |first1=R. K. |year=1997 |title=Importance of prairie wetlands and avian prey to breeding Great Horned Owls (Bubo virginianus) in northwestern North Dakota |journal=United States Department of Agricultural, Forest Service General Technical Report |pages=286–298}}</ref> Most prey is in the range of {{convert|4|g|oz|abbr=on}} ([[shrew]]s) to {{convert|2300|g|lb|abbr=on}} ([[Hare|jackrabbit]]s).<ref name="Cromrich" /><ref name="Jaksic2">{{cite journal |last1=Jaksić |first1=F. M. |last2=Marti |first2=C. D. |year=1984 |title=Comparative food habits of Bubo owls in Mediterranean-type ecosystems |journal=The Condor |volume=86 |issue=3 |pages=288–296 |doi=10.2307/1366997|jstor=1366997 |doi-access=free }}</ref> A single owl requires about {{convert|50|to|100|g|oz|abbr=on}} of food per day and can subsist on a large kill over several days.<ref name="DwightSmith">{{cite book|last=Smith|first=Dwight G.|title=Great Horned Owl|year=2002|publisher=Stackpole Books|location=Mechanicsburg, PA |url=https://books.google.com/books?id=f1PVJVWbQKwC |isbn=978-0-8117-2689-4 |pages=33, 80–81 |edition=1st|access-date=2013-03-21}}</ref> Despite the great diversity of prey taken by these predators, in most of the continental United States from the East to the Midwest as well as [[Canada]] and [[Alaska]], great horned owls largely live off just a handful of prey species: three species of [[Lagomorpha|lagomorph]]: the [[eastern cottontail]] (''Sylvilagus floridanus''), the [[snowshoe hare]] (''Lepus americanus'') and the [[black-tailed jackrabbit]] (''Lepus californicus''); two species of [[Peromyscus|New World mice]]: the [[white-footed mouse]] and the [[Peromyscus maniculatus|North American deermouse]] (''Peromyscus leucopus & maniculatus''); approximately three species of [[vole]]: the [[Meadow vole|meadow]], [[Prairie vole|prairie]] and [[woodland vole]]s (''Microtus pennsylvanicus, ochrogaster & pinetorum''); and one introduced pest, the brown rat.<ref name="Houston" /><ref name="Hamerstrom" /><ref name="Cromrich" />

===Rodents===
[[File:White-footed Mouse, Cantley, Quebec.jpg|thumb|right|A large portion of the great horned owl's food consists of small rodents, such as [[white-footed mouse|white-footed mice]].]]
Small [[rodent]]s form the great majority of great horned owl prey by number. Weighing a mere {{convert|14|to|31.5|g|oz|abbr=on}} and {{convert|20|to|58|g|oz|abbr=on}} on average, the nine species of New World mice in ''Peromyscus'' and eight species voles in ''Microtus'' recorded in the diet would appear to be overly small to be as important as they are to a predatory bird of this size. The prominence of these genera is undoubtedly due to the abundance of both genera in the wooded edge habitats frequented by great horned owls. It is estimated that a family of owls with two offspring would need to take about a half dozen (voles) to a dozen (mice) of these rodents every night to satisfy their dietary requirements but apparently the accessibility and abundance of these foods is irresistible as their numeric dominance is indisputable.<ref name= Craighead/><ref name= Hamerstrom/> By winter in areas that hold heavy snow, ''[[Peromyscus]]'' mice often come to outnumber the voles in the diet since the mice tend to travel over the surface of the snow while the voles make tunnels underneath the snow.<ref name= Craighead/><ref name= Voous/><ref name= Hamerstrom/> 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.<ref name= Hamerstrom/>  Great horned owls living in the timbered fringes of garbage or refuse dumps may subsist mostly on rats.<ref name= Mikkola/>

In the [[Rocky Mountains|Rockies]], California, the [[Southwestern United States]] and northern [[Mexico]], the diversity of this species' diet rises, in sync with the diversity of rodents. Especially important, from [[Colorado]] to [[Washington (state)|Washington state]] is the [[northern pocket gopher]] (''Thomomys talpoides''), although assorted other pocket gophers (''[[Geomys]], [[Cratogeomys]], [[Michoacan pocket gopher|Zygogeomys]], [[Pappogeomys]]'' and other ''[[Thomomys]]'' ssp.) are readily taken. While the northern weighs from {{convert|90|to|120|g|oz|abbr=on}}, other pocket gophers hunted average from {{convert|95|to|545|g|lb|abbr=on}} in mass. From [[Washington (state)|Washington]] to [[Baja California]] a very important food is the [[Heteromyidae|pocket mice]], primarily the [[Great Basin pocket mouse]] (''Perognathus parvus''). While the Great Basin species is a relative giant at {{convert|22|g|oz|abbr=on}}, other hunted pocket mice (which may include both ''[[Perognathus]]'' and ''[[Chaetodipus]]'' ssp.) can average nearly as light as {{convert|8|g|oz|abbr=on}}. In [[East Texas]], the {{convert|159|g|oz|abbr=on}} [[hispid cotton rat]] (''Sigmodon hispidus'') is the most commonly recorded prey species.<ref name= Parmalee>{{cite journal |last1=Parmalee |first1=P. W. |year=1954 |title=Food of the great horned owl and barn owl in east Texas |journal=The Auk |volume=71 |issue=4 |pages=469–470 |doi=10.2307/4081546|jstor=4081546 |doi-access=free }}</ref> The same species constituted 75% by number of a small sampling in [[Oklahoma]].<ref>{{cite journal |last1=Baumgartner |first1=A. M. |last2=Baumgartner |first2=F. M. |year=1944 |title=Hawks and owls in Oklahoma 1939–1942: Food habits and population changes |journal=The Wilson Bulletin |volume=56 |issue=4 |pages=209–215 |jstor=4157378}}</ref> In semi-desert and other arid habitats, [[kangaroo rat]]s become increasingly important prey, ten species have been reported in the diet but most prominently the [[Ord's kangaroo rat|Ord's]]  and [[Merriam's kangaroo rat]]s (''Dipodomys ordii & merriami''), both being widespread, numerous and relatively diminutive (at {{convert|42|and|48|g|oz|abbr=on}}). Eight known larger species of kangaroo rats, including the [[giant kangaroo rat]] (''Dipodomys ingens'') averaging at {{convert|152|g|oz|abbr=on}}, are also taken.<ref name= Fitch>{{cite journal |last1=Fitch |first1=H. S. |year=1947 |title=Predation by owls in the Sierran foothills of California |journal=The Condor |volume=49 |issue=4 |pages=137–151 |doi=10.2307/1364108|jstor=1364108 }}</ref><ref name= Murphy2>{{cite journal |last1=Murphy |first1=J. R. |last2=Camenzind |first2=F. J. |last3=Smith |first3=D. G. |last4=Weston |first4=J. B. |year=1969 |title=Nesting ecology of raptorial birds in central Utah |journal=Brigham Young University Science Bulletin-Biological Series |volume=10 |issue=4 |pages=1–36 |url=https://scholarsarchive.byu.edu/byuscib/vol10/iss4/1}}</ref><ref name= Fitch2>{{cite journal |last1=Fitch |first1=H. S. |year=1940 |title=Some observations on horned owl nests |journal=The Condor |volume=42 |issue=1 |pages=73–75 |doi=10.2307/1364321|jstor=1364321 }}</ref>

The [[squirrel]]s, including [[ground squirrel]]s, [[marmot]]s (''Marmota''), [[prairie dog]]s (''Cynomys''), [[chipmunk]]s and [[tree squirrel]]s, are diurnal and so are largely unavailable to great horned owls as prey. Occasionally though, one will be caught from their leaf nest, nest hole or burrow entrance first thing in the morning or in the late afternoon and approximately 35 species have been successfully predated by these owls. In general larger sized than other rodent families, the species hunting range from the {{convert|62|g|oz|abbr=on}} [[gray-collared chipmunk]] (''Tamias cinereicollis'') to the {{convert|5775|g|lb|abbr=on}} [[hoary marmot]] (''Marmota caligata''); thus, squirrels can provide a very fulfilling meal.<ref name= Bent/><ref name= Houston/><ref>{{cite web |url=http://www.birdnote.org/birdnote-transcript.cfm?id=1529 |title=Great Horned Owl Menu |publisher=Birdnote.org |date=2008-08-29 |access-date=2012-02-09 |archive-url=https://web.archive.org/web/20120310184307/http://www.birdnote.org/birdnote-transcript.cfm?id=1529 |archive-date=2012-03-10 }}</ref>  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 {{convert|4500|to|9000|g|lb|abbr=on}}. This has been determined from owls who have porcupine quills imbedded in them, sometimes resulting in death.<ref name= Bent/><ref name= Powell>{{cite book |last1=Powell |first1=B. |year=1984 |title=Labrador by choice |publisher=Jesperson Press |location=St. John's, NF |isbn=0-920502-31-8}}</ref> On occasion, they are successful in killing porcupine, even adults as determined by the size of the quills left behind and prey remains at bloodied kill sites.<ref name=DwightSmith/><ref>{{cite journal |last1=Eifrig |first1=H. |year=1909 |title=Great horned owl versus porcupine |journal=The Auk |volume=26 |pages=58–59 |url=https://books.google.com/books?id=SZ5-ZWceXswC&dq=%22Great+horned+owl+versus+porcupine%22+auk&pg=PA58}}</ref><ref>{{cite journal |last1=Wiley |first1=J.W. |year=1969 |title=A Case of Great Horned Owl Predation on a Porcupine |journal=The Condor |volume=71 |issue=1 |page=73 |doi=10.2307/1366054|jstor=1366054 }}</ref> Other rodents recorded as secondary prey in North America include [[New World flying squirrel|flying squirrels]] (''Glaucomys'' ssp.), the [[golden mouse]] (''Ochrotomys nuttalli''), [[Clethrionomys|red-backed vole]]s & [[bog lemming]]s (''Myodes'' & ''Synaptomys'' ssp.), the [[muskrat]] (''Ondatra zibethicus''), the [[northern grasshopper mouse]] (''Onychomys leucogaster''), the [[northern pygmy mouse]] (''Baiomys taylori'') and [[Jumping mouse|jumping mice]] (''Zapus'' & ''Napaeozapus'' ssp.).<ref name= Bent/><ref name= Houston/>

===Lagomorphs===
[[File:Black tailed jackrabbit.jpg|thumb|right|upright|[[Black-tailed jackrabbit]]s are an important food source for western great horned owls.]] 
Although generally no match for rodents in the sheer quantity of individuals, in terms of prey biomass, the most significant prey of North American great horned owls are [[hare]]s and [[rabbit]]s. About a dozen lagomorphs species are known to be hunted by the owl, from the relatively tiny {{convert|420|g|lb|abbr=on}} [[pygmy rabbit]] to adult [[jackrabbit]]s weighing more than {{convert|2000|g|lb|abbr=on}}.<ref name= Bent/><ref>Dobler, Frederick C., and Kenneth R. Dixon. "The pygmy rabbit Brachylagus idahoensis." Rabbits, hares, and pikas: status survey and conservation action plan (JA Chapman and JEC Flux, eds.). IUCN/SSC Lagomorph Specialist Group, Gland, Switzerland (1990): 111–115.</ref> These species are overall the largest regular prey for this species.<ref name= Voous/>

In [[Utah]], where great horned owls are dependent on the jackrabbits, average brood size rose from 2 at jackrabbit population lows to 3.3 when the jackrabbits were at their peak. At the peak of the population cycle, jackrabbits accounted for 90.2% and [[desert cottontail]]s (''Sylvilagus audubonii'') for another 8.7% of prey biomass.<ref name="Smith2" /><ref name="Smith3">{{cite journal |last1=Smith |first1=D. G. |first2=J. R. |last2=Murphy |year=1979 |title=Breeding responses of raptors to jackrabbit density in the eastern Great Basin Desert of Utah |journal=Raptor Research |volume=13 |pages=1–14 |url=https://archive.org/details/biostor-216510}}</ref> In the short-grass prairie of [[Colorado]], [[mountain cottontail]] (''Sylvilagus nuttallii'') and black-tailed jackrabbits predominated in October to December, making up 42.9% by number (and nearly all the biomass), thence dropping to 9.3% by number in April, while voles rose to 32.2% peak in May, down to a minimum of 10.2% by number in June.<ref name="Voous" /> 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.<ref name="Marti2">{{cite journal |last1=Marti |first1=C. D. |year=1969 |title=Some comparisons of the feeding ecology of four owls in north-central Colorado |journal=The Southwestern Naturalist |volume=14 |issue=2 |pages=163–170 |doi=10.2307/3668871|jstor=3668871 |bibcode=1969SWNat..14..163M }}</ref> 

In central Utah, the lagomorphs (black-tailed jackrabbit/desert cottontail) and Ord's kangaroo rat each made up 39% of the food by number, respectively.<ref name="Smith2" /> The mountain cottontail dominates the biomass of prey in the [[Sierra Nevada (U.S.)|Sierran foothills]] of California, making up 61.1% of the biomass, although are numerically secondary to desert woodrat.<ref name="Fitch" /> Remarkably, in the [[Morley Nelson Snake River Birds of Prey National Conservation Area]] of [[Idaho]], individual rodents (1159 counted) were more than 10 times more numerous than lagomorphs (114 counted) by quantity and yet the jackrabbit and mountain cottontail still made up approximately half of the biomass.<ref name="Marti, C. D. 1996">{{cite journal |last1=Marti |first1=C. D. |last2=Kochert |first2=M. N. |year=1996 |title=Diet and Trophic Characteristics of Great Horned Owls in Southwestern Idaho |journal=Journal of Field Ornithology |volume=67 |issue=4 |pages=499–506 |jstor=4514149|bibcode=1996JFOrn..67..499M }}</ref> 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'').<ref>{{cite journal |last1=Llinas-Gutirrez |first1=J. |last2=Arnaud |first2=G. |last3=Acevedo |first3=M. |year=1991 |title=Food habits of the Great Horned Owl in the Cape Region of Lower California, Mexico |journal=Journal of Raptor Research |volume=25 |issue=4 |pages=140–141}}</ref>

In the northern [[Taiga|boreal forest]], great horned owls are even more dependent on the snowshoe hare. At the peak of the 10-year hare cycle, snowshoe hares were by far the largest component of both summer and winter diets (77–81% and 90–99%, respectively, in [[Alberta]]; 83–86% and 75–98%, respectively, in [[Yukon]]). At the lowest point of the hare's cycle, summer diets consisted of only 0–16% snowshoe hare in Alberta and 12.7% in Yukon. When hares were scarce, great horned owls in these regions fed mostly on large [[rodent]]s, mice and voles, [[grouse]] and [[duck]]s. Because fewer of these alternative prey species are available in boreal forests during winter, owls had to emigrate or suffer high mortalities if they stayed.<ref name="Adamcik">{{cite journal |last1=Adamcik |first1=R. S. |first2=A. W. |last2=Todd |first3=L. B. |last3=Keith |year=1978 |title=Demographic and dietary responses of Great Horned Owls during a snowshoe hare cycle |journal=Canadian Field-Naturalist |volume=92 |issue=2 |pages=156–166 |doi=10.5962/p.346661 |issn=0008-3550|doi-access=free }}</ref><ref>{{cite journal |last1=Rohner |first1=C. |year=1995 |title=Great Horned Owls and snowshoe hares: what causes the time lag in the numerical response of predators to cyclic prey? |journal=Oikos |volume=74 |issue=1 |pages=61–68 |doi=10.2307/3545675|jstor=3545675 |bibcode=1995Oikos..74...61R }}</ref> In [[Alberta]], the local population of great horned owls can increase threefold from hare population lows to peaks.<ref name="Mcinvaille">{{cite journal |last1=Mcinvaille |first1=W. B. Jr. |first2=L. B. |last2=Keith |year=1974 |title=Predator-prey relations and breeding biology of the Great Horned Owl and Red-tailed Hawk in central Alberta |journal=Canadian Field-Naturalist |volume=88 |pages=1–20|doi=10.5962/p.344317 |doi-access=free }}</ref> The dependency on the snowshoe hare by the great horned owl extends into [[Alaska]] as well.<ref>{{cite journal |last1=Weir |first1=D. |first2=A. |last2=Hanson |year=1989 |title=Food habits of Great Horned Owls, Bubo virginianus, in the northern taiga of the Yukon Territory and Alaska |journal=Canadian Field-Naturalist |volume=103 |pages=12–17|doi=10.5962/p.356045 |doi-access=free }}</ref>

===Other mammals===
Other mammals are taken readily as well. Several species of [[Carnivora|mammalian carnivore]], such as [[Ring-tailed cat|ringtail]]s (''Bassariscus astutus''), [[American mink]]s (''Neogale vison''), [[American marten]]s (''Martes americana''), [[black-footed ferret]] (''Mustela nigripes'') and various other small [[mustelid]]s (''Mustela'' ssp.), are sometimes taken as prey.<ref name="Bent" /><ref name="Houston" /><ref>{{cite journal |last1=Bull |first1=E. L. |last2=Heater |first2=T. W. |year=2001 |title=Survival, Causes of Mortality, and Reproduction in the American Marten in Northeastern Oregon|journal=Northwestern Naturalist |volume=82 |issue=1 |pages=1–6|doi=10.2307/3536640 |jstor=3536640 }}</ref><ref>{{cite journal |last1=Mendall |first1=H. L. |year=1944 |title=Food of Hawks and Owls N Maine |journal=The Journal of Wildlife Management |volume=8 |issue=3 |pages=198–208 |doi=10.2307/3795698|jstor=3795698 }}</ref> In one case, a great horned owl was the likely killer of an adult female [[Fisher (animal)|fisher]] (''Martes pennanti''), though young ones are typically taken.<ref>Roger A. Powell, ''Martes pennanti'', "Mammalian Species", Issue 156, 8 May 1981, pp. 1–6, {{dot|10.2307/3504050}}</ref><ref>{{cite book |last1=Axelson |first1=G. |year=2012 |title=Fewer Fishers in the Forest |publisher=Minnesota Department of Natural Resources}}</ref> Prey in the form of [[Canidae|canids]], like [[fox]]es or [[coyote]]s (''Canis latrans'') are often juveniles presumably snatched from the mouths of dens by night.<ref name="Bent" /><ref name="Houston" /><ref>{{cite book |last1=Brown |first1=L. N. |year=1997 |title=A guide to the mammals of the southeastern United States |publisher=University of Tennessee Press |isbn= 0-87049-966-1}}</ref><ref>{{cite journal |last1=Storm |first1=G. L. |last2=Andrews |first2=R. D. |last3=Phillips |first3=R. L. |last4=Bishop |first4=R. A. |last5=Siniff |first5=D. B. |last6=Tester |first6=J. R. |year=1976 |title=Morphology, reproduction, dispersal, and mortality of midwestern red fox populations |journal=Wildlife Monographs |issue=49 |pages=3–82 |jstor=3830425}}</ref><ref name="Ray">{{cite web |last1=Ray |first1=J.D. |year=2012 |title=Great Silent Hunter |website=Birdwatching Magazine |location=Braintree, Massachusetts |url=https://www.birdwatchingdaily.com/news/species-profiles/great-silent-hunter/}}</ref> [[Kit fox|Kit]] and [[swift fox]]es of up to adult size may be taken.<ref name="DwightSmith" /><ref>{{cite journal |last1=Sovada |first1=M. A. |last2=Roy |first2=C. C. |last3=Bright |first3=J. B. |last4=Gillis |first4=J. R. |year=1998 |title=Causes and rates of mortality of swift foxes in western Kansas |journal=The Journal of Wildlife Management |volume=62 |issue=4 |pages=1300–1306 |doi=10.2307/3801994|jstor=3801994 |bibcode=1998JWMan..62.1300S }}</ref><ref>{{cite journal |last1=Kilgore |first1=D.L. |year=1969 |title=An ecological study of the swift fox (Vulpes velox) in the Oklahoma panhandle |journal=American Midland Naturalist |volume=81 |issue=2 |pages=513–534 |doi=10.2307/2423986|jstor=2423986 }}</ref>

The most regular predatory association amongst relatively larger carnivores is that with skunks. Due to their poor sense of smell, great horned owls are the only predators to routinely attack these bold mammals with impunity. All six skunk species found in North America are reported as prey, including full-grown [[striped skunk]]s (''Mephitis mephitis''), which can be three times as heavy as the attacking owl.<ref name="Bent" /><ref name="Cromrich" /><ref>{{cite journal |last1=Huey |first1=L. M. |year=1931 |title=Skunks as Prey for Owls |journal=The Wilson Bulletin |page=224 |url=https://sora.unm.edu/sites/default/files/journals/wilson/v043n03/p0224-p0224.pdf}}</ref> In one single nest, the remains of 57 striped skunks were found.<ref name="Hunter_Carnivores">{{cite book|last=Hunter|first=Luke|title=Carnivores of the World|year=2011|publisher=Princeton University Press|location=Princeton, NJ|isbn=978-0-691-15228-8}}</ref> Due to the proclivity of skunk predation, great horned owls nests frequently smell strongly of skunk and occasionally stink so powerfully of skunk that they leave the smell at kill sites or on prey remains.<ref name="Houston" /><ref name="Crocoll">{{cite thesis |last1=Crocoll |first1=S. T. |year=1984 |title=Breeding biology of broad-winged and red-shouldered hawks in western New York |type=Doctoral dissertation |publisher=State University of New York at Fredonia, Department of Biology |url=https://sora.unm.edu/node/53153}}</ref> Surprisingly, at least two cases of a great horned owl preying on an adult [[raccoon]] (''Procyon lotor'') have been reported.<ref name="Bosakowski">{{cite journal |last1=Bosakowski |first1=T. |first2=R. |last2=Speiser |first3=D. G. |last3=Smith |year=1989 |title=Nesting ecology of forest-dwelling Great Horned Owls in the Eastern Deciduous Forest Biome |journal=Canadian Field-Naturalist |volume=103 |pages=65–69|doi=10.5962/p.356054 |doi-access=free }}</ref><ref>{{cite web |url=http://mariewin.server304.com/johnblog/2005/07/blakeman-answers-questions-about-nest.html |title=Blakeman answers questions about nest maintenance |publisher=Blakeman on Hawks |access-date=6 July 2005 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304040936/http://mariewin.server304.com/johnblog/2005/07/blakeman-answers-questions-about-nest.html }}</ref> One instance of an owl taking a [[bobcat]] (''Lynx rufus'') as prey was also reportedly observed.<ref name="DwightSmith" />  Occasionally, domestic carnivores are also prey. A few cases of young or small [[dog]]s (''Canis lupus familiaris'')<ref name="CNN_chihuahua">{{cite web|last=Olson|first=Karen|title=Chihuahua survives owl attack in Illinois|url=http://www.cnn.com/2011/US/01/19/illinois.dog.attacked/index.html?hpt=C2|publisher=CNN|access-date=21 March 2013|date=January 19, 2011}}</ref><ref>{{cite web|last=Johansson|first=Tait|url=http://www.bedfordaudubon.org/birds/ghow01.html|title=The Great Horned Owl|publisher=Bedford Audubon Society|access-date=2012-02-09|archive-url=https://web.archive.org/web/20120320195411/http://www.bedfordaudubon.org/birds/ghow01.html|archive-date=2012-03-20}}</ref> and several of juvenile and adult [[cat]]s (''Felis silvestris catus'') being killed by great horned owls have been reported.<ref name="Bent" /><ref name="Ray" /><ref>Forbush, Edward H. "The Great Horned Owl (1927)." The Essential Naturalist: Timeless Readings in Natural History (2011): 15.</ref><ref>{{cite book |last1=Deal |first1=K. |year=2010 |title=Wildlife and Natural Resource Management |publisher=Cengage Learning |isbn=978-1-305-62774-1}}</ref><ref>{{cite web|title=Beware of the Great Horned Owl|url=http://helpfindlostpets.com/birds/beware-of-the-great-horned-owl|publisher=Help Find Lost Pets|access-date=21 March 2013|date=May 27, 2010|archive-url=https://web.archive.org/web/20120303102227/http://helpfindlostpets.com/birds/beware-of-the-great-horned-owl|archive-date=3 March 2012}}</ref><ref name="RaptorCenter">{{cite web|title=Great Horned Owl – Bubo virginianus|url=http://www.raptorcenter.org/great-horned-owl.asp|publisher=Raptor Education Center|access-date=21 March 2013}}</ref>

Aside from carnivorans, various other mammals are taken as supplemental prey. At least eight species of [[shrew]]s are taken by opportunity and make up the smallest mammalian prey taken by great horned owls, as specimens of [[least shrew]] (''Cryptotis parva'') or [[masked shrew]] (''Sorex cinereus'') have had an estimated weight of only {{convert|2|g|oz|abbr=on}}.<ref name= Cromrich/> One of the more regularly taken shrews, though, is the larger {{convert|19.5|g|oz|abbr=on}} [[northern short-tailed shrew]] (''Blarina brevicauda''), which was represented in more than 2% of pellets in the [[Upper Midwest]].<ref name="Hamerstrom" /> [[Mole (animal)|Mole]]s, of at least four or five species, are also widely but lightly reported as prey.<ref name="Hamerstrom" /><ref name="Cromrich" /> From both the tropics and the United States, several species of opossum may be taken, down to the size of the tiny [[dwarf fat-tailed mouse opossum]] (''Thylamys velutinus'').<ref>James T. Pokines "Prey Remains from a Great Horned Owl (Bubo virginianus) Roost in the Icla Valley, Bolivia," Journal of Raptor Research 41(2), 174–175, (1 June 2007). {{doi|10.3356/0892-1016(2007)41[174:PRFAGH]2.0.CO;2}}</ref> In [[Brazil]], juvenile [[white-eared opossum]] (''Didelphis albiventris'') weighing around {{convert|1000|g|lb|abbr=on}} were found in 12% of pellets weighing about.<ref>Tomazzoni, Ana C., Ezequiel Pedó, and Sandra M. Hartz. "Food habits of Great Horned Owls (Bubo virginianus) in the breeding season in Lami Biological Reserve, southern Brazil." Ornitologia Neotropical 15.2 (2004): 279–282.</ref> North American subspecies can prey on larger [[Virginia opossum]] (''Didelphis virginianus'') readily, and can be a major predator of this species.<ref>Gardner, Alfred L. "Virginia opossum." Wild mammals of North America: biology, management, and economics. Johns Hopkins University Press, Baltimore, MD (1982): 3–36.</ref><ref name="Wink">{{cite journal |last1=Wink |first1=J.E. |last2=Senner |first2=S. E. |last3=Goodrich |first3=L. J. |year=1987 |title=Food habits of great horned owls in Pennsylvania |journal=Proceedings of the Pennsylvania Academy of Science |volume=61 |issue=2 |pages=133–137 |jstor=44111738}}</ref> Remnants of [[armadillo]], presumably [[nine-banded armadillo]] (''Dasypus novemcinctus''), have been found around owl nests in the south.<ref name="Bent" /> 11 species of bat are known to be hunted by great horned owls.<ref name="Voous" /><ref name="Burns">{{cite journal |last1=Burns |first1=B. J. |year=1952 |title=Food of a Family of Great Horned Owls, Bubo virginianus, in Florida |journal=The Auk |volume=69 |issue=1 |pages=86–87 |doi=10.2307/4081300|jstor=4081300 |doi-access=free }}</ref><ref>{{cite journal |last1=Baker |first1=J. K. |year=1962 |title=The manner and efficiency of raptor depredations on bats |journal=The Condor |volume=64 |issue=6 |pages=500–504 |doi=10.2307/1365473|jstor=1365473 }}</ref><ref name="Kittredge">{{cite journal |last1=Kittredge |first1=V. C. |last2=Wilson |first2=P. W. |last3=Caire |first3=W. |year=2007 |title=An updated checklist of the food items of the great horned owl (Bubo virginianus: Strigiformes: Strigidae) in Oklahoma |journal=Proceedings- Oklahoma Academy of Science |volume=86 |url=https://ojs.library.okstate.edu/osu/index.php/OAS/article/view/5811}}</ref> One pellet in [[Texas]] was found to be composed entirely of [[Mexican free-tailed bat]]s (''Tadarida brasiliensis'').<ref>{{cite journal |last1=Twente |first1=J. W. |year=1954 |title=Predation on bats by hawks and owls |journal=The Wilson Bulletin |volume=66 |issue=2 |pages=135–136 |url=https://sora.unm.edu/node/127345}}</ref>

===Birds===
[[File:American Coot Image 001.jpg|thumb|right|[[American coot]]s are often a favored food source for great horned owls living near wetlands.]]
After mammals, birds rank as the next most important general prey group. Birds are usually considerably secondary in the diet but outnumber the mammals in the diet by diversity, as more than 250 species have been killed in North America alone. Statistically, the most significant avian prey seems to be [[Galliformes|galliforms]], of which they are known to have preyed on 23 species, basically consisting of all of the native species found in the [[United States]].<ref name= Bent/><ref name= Houston/> In the [[Upper Midwest]], the [[ring-necked pheasant]] (''Phasianus colchicus'') and [[northern bobwhite]] (''Colinus virginianus'') were the fifth and sixth (out of 124 identified species) most significant prey species in 4838 pellets.<ref name= Hamerstrom/> Errington characterized the predatory pressure exerted on bobwhites by great horned owls as "light but continuous pressure", which may be considered characteristic of the species' hunting of all galliforms.<ref name= Errington2>{{cite journal |last1=Errington |first1=P. L. |year=1932 |title=Food habits of southern Wisconsin raptors. Part I. Owls |journal=The Condor |volume=34 |issue=4 |pages=176–186 |doi=10.2307/1363563|jstor=1363563 }}</ref>

Usually coveys of quail are partially protected by spending the night roosting communally in dense thickets but should a hunting owl be able to track down the communal roost, losses can be fairly heavy until the roost relocates.<ref name="Craighead" /> Similarly, owls may track down sleeping [[grouse]], which also roost in vegetation but more openly than quail. Some grouse, such as [[greater prairie-chicken]] (''Tympanuchus cupido''), [[sharp-tailed grouse]] (''Tympanuchus phasianellus'') and [[greater sage-grouse]] (''Centrocercus urophasianus''),  may also been vulnerable to great horned owls while displaying conspicuously in openings on a [[Lek mating|lek]] first thing in the morning.<ref name="Hamerstrom2">{{cite journal |last1=Hamerstrom |first1=F. N. |year=1939 |title=A study of Wisconsin prairie chicken and sharp-tailed grouse |journal=The Wilson Bulletin |volume=51 |issue=2 |pages=105–120 |jstor=4156820}}</ref> In the boreal forest, especially in years where the snowshoe hare experiences population decreases, great horned owls prey fairly heavily (approximately 25% of biomass) on [[ruffed grouse]] (''Bonasa umbellus'') and [[spruce grouse]] (''Falcipennis canadensis''), enough so in the earlier bird to possibly contribute to population reductions.<ref name="Adamcik" /><ref>{{cite journal |last1=Keith |first1=L. B. |first2=D. H. |last2=Rusch |year=1988 |title=Predation's role in the cyclic fluctuations of Ruffed Grouse |journal=Proceeding International Congress of Ornithology |volume=19 |pages=699–732 |url=http://www.barbau.ca/content/predations-role-cyclic-fluctuations-ruffed-grouse }}{{Dead link|date=June 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Larger species of galliform are not immune to predation either. On [[Protection Island (Washington)|Protection Island]] in [[Washington (state)|Washington state]], introduced [[common peafowl]] (''Pavo cristatus'') are an important prey item.<ref name="Hayward">{{cite journal |last1=Hayward |first1=J. L. |first2=J. G. |last2=Galusha |first3=G. |last3=Frias |year=1993 |title=Analysis of Great Horned Owl pellets with Rhinoceros Auklet remains |journal=The Auk |volume=110 |issue=1 |pages=133–135 |url=https://sora.unm.edu/node/25221}}</ref> The [[wild turkey]] (''Meleagris gallopavo''), {{convert|4|to|8|kg|lb|abbr=on}} on average between the sexes, is probably the largest bird the great horned owl hunts in which they kill adults. Both full-grown wild turkeys<ref>{{cite journal |last1=Schemnitz |first1=S. D. |first2=D. L. |last2=Goerndt |first3=H. |last3=Jones |year=1985 |title=Habitat needs and management of Merriam's turkeys in southcentral New Mexico |journal=Proceedings of National Wild Turkey Symposium |volume=5 |pages=199–232}}</ref> and adult domestic turkeys<ref name="Bent" /> have been hunted and killed. Under normal circumstances, [[Chicken|domestic chicken]] (''Gallus gallus domesticus'') will be ignored in favor of wild prey. On occasion, individual owls, especially inexperienced juveniles, will become habitual fowl killers. These errant owls mainly hunt chickens, though will also take domestic [[guineafowl]], turkeys and anything else available.<ref name="Hamerstrom" /> In general, chickens kept in locked cages with enclosed tops overnight are safe from great horned owls; not so chickens left free range or in open enclosures.<ref name="Bent" />

While galliforms are widely reported, the few cases where great horned owls locally turn to birds as the primary food source over mammals, these may often be local responses to the abundance of breeding [[water bird]]s or concentrations of roosting water birds, since they tend to roost in relatively open spots. They have been known to predate more than 110 different species of assorted water bird.<ref name= Voous/> In prairie wetlands of [[North Dakota]], avian prey, primarily represented by [[duck]]s and the [[American coot]] (''Fulica americana'') came to represent 65% by number and 83% by biomass of the diet of the local owls, also including secondarily [[grebe]]s, smaller [[Rail (bird)|rails]], [[loon]]s, [[Wader|shorebird]]s and [[seabird]]s, as well as upland-based species like [[grey partridge]] (''Perdix perdix''), [[sharp-tailed grouse]] and [[passerine]]s.<ref name=PF>{{cite web | url=https://www.peregrinefund.org/explore-raptors-species/owls/great-horned-owl | title=Great Horned Owl &#124; the Peregrine Fund }}</ref> 77% of the ducks in that study were juveniles, the largest duck being a male [[mallard]] (''Anas platyrhnychos'') weighing approximately {{convert|1250|g|lb|abbr=on}}, but nearly all the coots were adults.<ref name= Murphy/> On [[Protection Island (Washington)|Protection Island]], [[Washington (state)|Washington]], where they are no native land mammals, [[rhinoceros auklet]]s (''Cerorhinca monocerata''), both adults and nestlings, were the most numerous prey, present in 93% of 120 pellets.<ref name= Hayward/> Species as large as adult [[Canada goose|Canada geese]], [[snow goose]]<ref name= Bent/><ref name= Hamerstrom/> and [[great blue heron]]s<ref name= Houston/> have been successfully killed. Medium-sized birds of prey (even other species of owl) are also taken.<ref>König, Claus, Friedhelm Weick, and Jan-Hendrik Becking. Owls of the World. 2nd ed. Bloomsbury Publishing, 2009. Web. 23 May. 2023.</ref> The nestlings of even larger species like [[trumpeter swan]]s (''Cygnus buccinator''),<ref>{{cite journal |last1=Monnie |first1=J. B. |year=1966 |title=Reintroduction of the Trumpeter Swan to its former prairie breeding range |journal=Journal of Wildlife Management |volume=30 |issue=4 |pages=691–696 |doi=10.2307/3798274|jstor=3798274 }}</ref> [[American white pelican]]s (''Pelecanus eryhtrorhynchos''),<ref>{{cite book |last1=Knopf |first1=F. L. |first2=R. M. |last2=Evans |year=2020 |chapter=American White Pelican (''Pelecanus erythrorhynchos''), version 1.0 |title=Birds of the World |editor-first1=A. F. |editor-last1=Poole |publisher=Cornell Lab of Ornithology |location=Ithaca, NY |doi=10.2173/bow.amwpel.01|s2cid=216485857 }}</ref> [[brown pelican]]s (''Pelecanus occidentalis'')<ref>{{cite journal |last1=Schreiber |first1=R. W. |first2=R. W. |last2=Risebrough |year=1972 |title=Studies of the Brown Pelican |journal=The Wilson Bulletin |volume=84 |issue=2 |pages=119–135 |jstor=4160189}}</ref> and [[sandhill crane]]s (''Grus canadensis'')<ref>{{cite journal |last1=Littlefield |first1=C. D. |year=2003 |title=Sandhill Crane nesting success and productivity in relation to predator removal in southeastern Oregon |journal=The Wilson Bulletin |volume=115 |issue=3 |pages=263–269 |doi=10.1676/02-108 |jstor=4164569|s2cid=86244240 |url=https://www.biodiversitylibrary.org/part/210428 }}</ref> have also been killed by these owls.

Other assorted birds are taken seemingly at random opportunity. The predatory effect of this species on other raptorial birds, which is often considerable, is explored in the following section. In [[Brazil]], it was found in a small study that birds overall outnumbered mammals in pellets, although most were not determined to species and the ones that were shown a tremendously diverse assemblage of birds with no obvious dietary preference.<ref name= Tomazzoni>{{cite journal |last1=Tomazzoni |first1=A. C. |last2=Pedó |first2=E. |last3=Hartz |first3=S. M. |year=2004 |title=Food habits of Great Horned Owls (Bubo virginianus) in the breeding season in Lami Biological Reserve, southern Brazil |journal=Ornitologia Neotropical |volume=15 |issue=2 |pages=279–282 |s2cid=90637198 }}</ref> Although not usually numerically significant, 86 species of [[passerine]] have been taken by great horned owls. Members from most North American families are known as prey, although among smaller types such as [[chickadee]]s, [[New World warbler|warbler]]s, [[New World sparrow|sparrow]]s, [[Cardinalidae|cardinalids]], [[wren]]s and most [[tyrant flycatcher]]s only a few species from each have been recorded. Nonetheless, an occasionally unlucky migrant or local breeder is sometimes snatched.<ref name= Voous/><ref name= Bent/><ref name= Hamerstrom/> Fledgling songbirds are regularly taken in spring and summer.<ref name=DwightSmith/> The smallest avian prey known for great horned owls are the {{convert|5.8|g|oz|abbr=on}} [[blue-grey gnatcatcher]] (''Polioptila caerulea'') and the {{convert|6.2|g|oz|abbr=on}} [[ruby-crowned kinglet]] (''Regulus calendula'').<ref name= Hamerstrom/> Somewhat larger bodied families are more prominent, i.e. the [[corvid]]s (14 species) and [[icterid]]s (14 species) and, secondarily, the [[kingbird]]s (''Tyrannus'' ssp.), [[Thrush (bird)|thrushes]], [[mimid]]s and [[European starling]] (''Sturnus vulgaris'').<ref name= Voous/><ref name= Bent/><ref name= Hamerstrom/> This is likely due to the fact that the larger passerines usually roost in relatively open spots and have larger, more conspicuous nests. [[Crow]]s and [[raven]]s tend to be grabbed off of their communal roosts by night.<ref name= Houston/>

===Other prey===
The great horned owl rarely misses an opportunity to hunt [[reptile]]s and [[amphibian]]s. However, [[lizard]]s are largely unavailable as prey due to their typically diurnal periods of activity.<ref name= Houston/> However, some snakes are partially or largely nocturnal, and more than a dozen species are hunted in North America. Snakes hunted range from small, innocuous [[garter snake]]s (''Thamnophis'' ssp.) and [[night snake]]s (''Hypsiglena torquata'') to venomous species like [[Agkistrodon piscivorus|cottonmouth]]s (''Agkistrodon piscivorus'') and [[Crotalus viridis|prairie rattlesnake]]s (''Crotalus virdis'') and formidable, large species like [[Lampropeltis getula|common king snake]]s (''Lampropeltis getula'') and [[Western rat snake|black rat snake]]s (''Pantherophis obsoletus''), which in mature specimens can rival the owl in mass and sheer predatory power.<ref name= Bent/> The capture of the hatchlings of very large reptiles such as [[loggerhead turtle]]s (''Caretta caretta'') and [[American alligator]]s (''Alligator mississippiensis'') by great horned owls has been reported, in both cases likely when the baby reptiles are attempting to make their way to the security of water.<ref name= Bent/><ref>{{cite journal |last1=Toland |first1=B. |year=1991 |title=Great horned owl predation of Atlantic loggerhead turtle hatchlings |journal=Florida Field Naturalist |volume=19 |issue= |pages=117–119 |url=https://sora-dev.unm.edu/node/134434}}</ref> On rare occasion, [[salamander]]s, [[frog]]s and [[toad]]s are reported as prey.  On rare occasions, fish are taken including [[goldfish]] (''Carassius auratus''), [[bluegill]] (''Lepomis macrochirus''), [[Ameiurus|bullhead]]s (''Ameiurus'' ssp.), other [[catfish]], [[Catostomidae|suckers]], [[Centrarchidae|sunfish]], [[eel]]s and [[Cyprinidae|dace and chub]].<ref name= Bent/><ref name=DwightSmith/>

Many types of invertebrates are recorded as prey. These include mainly insects, but also [[crayfish]], [[crab]]s, [[centipede]]s, [[spider]]s, [[scorpion]]s and [[worm]]s.<ref name=PF/> The occasionally invertebrate prey taken largely consists of common, large insects such as various [[beetle]]s, [[crickets]], [[grasshopper]]s, [[Nepomorpha|water bug]]s and [[Tettigoniidae|katydid]]s, some of which the great horned owl has even reportedly caught via "hawking", i.e. swooping at on the wing.<ref name="Bent" /><ref name="Houston" /><ref>{{cite journal |last1=Duncan |first1=J.R. |last2=Lane |first2=P.A. |year=1998 |title=Great Horned Owl Observed Hawking 'Insects' |journal=Journal of Raptor Research |volume=22 |issue=3 |page=93 |url=https://sora.unm.edu/node/53103}}</ref> In some cases, the content of insects in great horned owl pellets may actually be due to the owls eating other birds which have freshly eaten insects in their own stomachs.<ref name="Hamerstrom" /> It is commonly believed that routine insectivory in great horned owls is mainly restricted to inexperienced young owls too unskilled to graduate to larger prey yet. It is clearly inefficient for owls of this size to attempt to raise young on a diet of foods as small as insects.<ref name="Marti" /> Although rare, [[carrion]]-feeding has been recorded in great horned owls, especially ones wintering in Canada and other northern areas during harsh weather.<ref>{{cite journal |last1=Errington |first1=P. L. |year=1938 |title=The Great Horned Owl as an indicator of vulnerability in prey populations |journal=The Journal of Wildlife Management |volume=2 |issue=4 |pages=190–205 |doi=10.2307/3795666|jstor=3795666 }}</ref> Road kills are sometimes opportunistically eaten. A case of an owl scavenging a [[white-tailed deer]] (''Odocoileus virginianus'') carcass, ultimately tearing off the deer's leg, was captured on a motion capture video camera set out to film wildlife.<ref>{{cite web |url= http://www.twincitiesnaturalist.com/2011/03/great-horned-owl-on-motion-camera-birds.html |title=Great Horned Owl on Motion Camera |author=Mona, K. |publisher=Twin Cities Naturalist |access-date=2016-11-29}}</ref>

===Urban vs rural diet===
Studies comparing the diets of rural and urban great horned owls have identified that the most abundant rodent prey in their environment fulfils the majority of their diet.<ref name=":1">{{Cite journal|last1=Hindmarch|first1=Sofi|last2=Elliott|first2=John E.|date=2015-02-04|title=Comparing the diet of Great Horned Owls (''Bubo virginianus'') in rural and urban areas of southwestern British Columbia|journal=The Canadian Field-Naturalist|volume=128|issue=4|page=393|doi=10.22621/cfn.v128i4.1634|issn=0008-3550|doi-access=free}}</ref><ref name=":3">{{Cite journal|last=Kopij|first=G|date=2012|title=Food niche overlap in co-existing Barn Owl Tyto alba (Scopoli 1769) and Great Horned Owl Bubo virginianus Gmelin 1788 in intensively used farmland|url=https://www.researchgate.net/publication/287217024|journal=Pol. J. Ecol|volume=61|pages=179–181}}</ref><ref>{{Cite journal|last1=Rullman|first1=Stan|last2=Marzluff|first2=John M.|date=2014|title=Raptor Presence Along an Urban–Wildland Gradient: Influences of Prey Abundance and Land Cover|journal=Journal of Raptor Research|volume=48|issue=3|pages=257–272|doi=10.3356/jrr-13-32.1|s2cid=86034385|issn=0892-1016|doi-access=free}}</ref><ref>{{Cite journal|last1=Chace|first1=Jameson F.|last2=Walsh|first2=John J.|date=2006|title=Urban effects on native avifauna: a review|url=https://linkinghub.elsevier.com/retrieve/pii/S016920460400146X|journal=Landscape and Urban Planning|language=en|volume=74|issue=1|pages=46–69|doi=10.1016/j.landurbplan.2004.08.007|bibcode=2006LUrbP..74...46C |url-access=subscription}}</ref> 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.<ref name=":3" /> In southwestern [[British Columbia]], [[Townsend's vole]]s were the most common prey species, while consumption of rats increased as the nesting location became more urban and rats replaced voles as the most abundant and stable food source.<ref name=":1" />  A similar focus on rats was found in populations in urban parks in [[Seattle]].<ref name=":0">{{Cite journal|last=Lambert|first=Anthony|date=1981|title=Presence and Food Preferences of the Great Horned Owl in the Urban Parks of Seattle|journal=The Murrelet|volume=62|issue=1|pages=2–5|doi=10.2307/3534439|jstor=3534439}}</ref>  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 [[rodenticide]]s.<ref>{{Cite journal|last1=Stone|first1=Ward B.|last2=Okoniewski|first2=Joseph C.|last3=Stedelin|first3=James R.|title=Poisoning of Wildlife with Anticoagulant Rodenticides in New York|date=April 1999|journal=Journal of Wildlife Diseases|volume=35|issue=2|pages=187–193|doi=10.7589/0090-3558-35.2.187|pmid=10231745|s2cid=22823380|issn=0090-3558}}</ref>

===Interspecific predatory relationships===
[[File:Hawk eating prey.jpg|thumb|right|An immature red-tailed hawk eats a vole, one of the many prey items that feed both the competing hawks and great horned owls.]]
Due to their very broad dietary habits, the great horned owls share their prey with many other predators, including avian, mammalian and reptilian ones. Almost every study comparing the diets of North American owls illustrates the considerable overlap in the dietary selection of these species, as all species, besides the primarily insectivorous varieties, rely on many of the same small rodent species for most of their diet, extending from the small northern saw-whet owl and [[eastern screech owl]] to the great horned and great grey owls.<ref name= Marti/><ref name= Cromrich/>

In a long-term study of a block of [[Michigan]], all nine species of accipitrid, falcon and owl that stayed to breed there were found to be primarily dependent on the same two rodent genera, the [[meadow vole]] and the two common ''[[Peromyscus]]'' species.<ref name= Craighead/> In the [[Great Basin]], the owls share black-tailed jackrabbit and [[desert cottontail]] as the primary prey with golden eagles, red-tailed hawks and [[ferruginous hawk]]s (''Buteo regalis''); all four species had diets with more than 90% of the biomass is made up of those lagomorphs. Of these, the great horned owl and golden eagle were able to nest most closely to one another because they had the most strongly dissimilar periods of activity.<ref name= Smith/><ref name= Smith3/> In California, when compared to the local red-tailed hawks and [[Crotalus atrox|western diamondback rattlesnake]]s (''Crotalus atrox''), the diets were most similar in that by number about 15–20% of all three species' diets depended on [[Cottontail rabbit|cottontail]]s, but the largest portion was made up of [[ground squirrel]]s in the hawk and the rattlesnake and desert woodrats and other assorted [[rodent]]s in the great horned owl.<ref name= Fitch/> In the [[Taiga|boreal forests]], the great horned owl's prolificacy as a [[snowshoe hare]] hunter places it second only to the [[Canada lynx]] (''Lynx canadensis'') among all predators. Although locally dependent on the hares as their main food, [[northern goshawk]]s (''Accipiter gentilis''), red-tailed hawks and golden eagles apparently do not have as large of an impact on the hares, nor do mammalian carnivore generalists that also kill many hares, like the [[Fisher (animal)|fisher]], [[bobcat]], [[wolverine]] (''Gulo gulo''), [[coyote]] and larger varieties (i.e. [[Gray wolf|wolves]] (''Canis lupus''), [[cougar]]s (''Puma concolor'') and [[bear]]s (''Ursus'' ssp.)).<ref name= Rohner/><ref name= Houston2/><ref name= Mcinvaille/><ref>WLM. (1918). ''Bird Enemies of the Varying Hare''. The Auk, 372–373.</ref>

The relationship between great horned owls and other raptorial birds in its range is usually decidedly one-sided. While certain species, such as the red-tailed hawk and [[northern goshawk]], might be seen as potential competition for the owls, most others seem to be regarded merely as prey by great horned owls. The great horned owl is both the most prolific and diverse predator in America of other birds of prey, with other accomplished raptor-hunters such as the goshawk and the golden eagle being more restricted in range, habitat and number in North America and thus having a more minor impact. All studies have found raptors are a small portion of this owl's diet but predation can be seriously detrimental for such prey, as raptors tend to be territorial and sparsely distributed as a rule and thus can be effectively decimated by a small number of losses.<ref name= Voous/><ref name= Cromrich/> In the [[gray hawk]] (''Buteo plagiatus''), for example, in a study of one breeding block of [[Arizona]], the owls were observed to visit nests nightly until all the nestlings were gone.<ref>Bibles, Brent D., Richard L. Glinski and R. Roy Johnson. 2002. ''Gray Hawk (Buteo plagiatus)'', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.</ref>

Raptorial birds in general tend to have large, conspicuous nests which may make them easier for a hunting owl to locate. The great horned owl gains an advantage by nesting earlier than any other raptor in its range (indeed any bird), as it is able to exploit the other raptors as food while in a more vulnerable state as their own nestlings have become well developed.<ref name= Craighead/> On average, great horned owls begin nesting about three weeks before red-tailed hawks begin to build nests, although some raptors may locally breed as much as two months after the owls.<ref name= Houston/><ref name= Dunstan>Dunstan, T. C., & Harrell, B. E. (1973). ''Spatio-temporal relationships between breeding red-tailed hawks and great horned owls in South Dakota''. Raptor Research, 7(2), 49–54.</ref>

More so than diurnal varieties of raptor, fairly significant numbers of owls are hunted, as all species are to some extent nocturnal and thus their corresponding activity can attract the horned owl's unwanted attention. The extent of predation on other owls depends on the habitat preferences of the other species. Eastern and western screech owls may be most vulnerable since they prefer similar wooded edge habitat. In a block of [[Wisconsin]], great horned owls were responsible for the failure of 78% of eastern screech owl's nests.<ref name= Craighead/> Long-eared owls and, to a lesser extent, barn owls tend to hunt in open, sparsely treed habitats more so than great horned owls, but since they may return to wooded spots for nesting purposes, they may be more vulnerable there. The long-eared owl and barn owls are often compared to the great horned owl as these medium-sized species often occur in abutting habitats and often hunt primarily the same vole and mice species, although the alternate prey of the great horned tends to be much larger, including the smaller owls themselves.<ref name= Earhart/><ref name= Rudolph/><ref>Barrows, C. W. (1989). Diets of five species of desert owls. Western Birds, 20(1), 1–10.</ref> In a pair of studies from [[Colorado]], the average weight of prey for long-eared owls was {{convert|28|to|30|g|oz|abbr=on}}, {{convert|46|to|57.1|g|oz|abbr=on}} for barn owl and {{convert|177|to|220|g|oz|abbr=on}} for the great horned owl.<ref name= Marti/><ref name= Marti2/>

Both young and adult great grey owls, despite their superficially superior size, are apparently hunted with impunity by great horned owls. In the boreal forests, both the northern hawk owl and great grey owl appear to be in greater danger of great horned owl predation in years where the snowshoe hare have low populations.<ref name= Duncan>Duncan, J. R. 1987. ''Movement strategies, mortality, and behavior of radio-marked Great Gray Owls in southeastern Manitoba and northern Minnesota''. Pages 101–107 in Biology and conservation of northern forest owls: Symposium proceedings, February 3–7, Winnipeg, MB. (Nero, R. W., R. J. Clark, R. J. Knapton, and R. H. Hamre, Eds.) General Technical Report, RM-142. Fort Collins, CO: USDA, Forest Service, Rocky Mountain Forest and Range Experiment Station.</ref><ref>Rohner, C., Smith, J. N., Stroman, J., Joyce, M., Doyle, F. I., & Boonstra, R. (1995). ''Northern hawk-owls in the nearctic boreal forest: prey selection and population consequences of multiple prey cycles''. Condor, 208–220.</ref> Great horned owls were the leading cause of mortality in juvenile spotted owls (30% of losses) and juvenile great grey owls (65% of losses).<ref name= Duncan/><ref>Forsman, E. D., Anthony, R. G., Reid, J. A., Loschl, P. J., Sovern, S. G., Taylor, M., & Seaman, D. E. (2002). ''Natal and breeding dispersal of northern spotted owls''. Wildlife Monographs, 1–35.</ref> Less is known about relations with the snowy owl, which may compete with great horned owls for food while invading south for the winter. Anecdotally, both snowy and great horned owls have rarely been reported to dominate or even kill one another depending on the size and disposition of the individual owls, although the snowy's preference for more open areas again acts as something of a buffer. The snowy may be the one North American owl too formidable for the great horned owl to consider as prey.<ref name= Potapov/>

Whereas owls of any age are freely attacked by great horned owls whether nesting or not, when it comes to diurnal raptors, great horned owls are mainly a danger around the nest. They often hunt diurnal raptors when they come across their often relatively conspicuous active platform nests during hunting forays in spring and summer, taking numbers of both nestlings and brooding adults.<ref name= Houston/> Again, like owls, diurnal raptors are attacked depending on the relative similarity of their habitat preferences to the owl. [[Cooper's hawk]]s (''Accipiter cooperii'') and red-tailed hawks tend to be most vulnerable, as they prefer the same wooded edges frequented by great horned owls. Other diurnal raptors may be attracted to more enclosed wooded areas, such as [[sharp-shinned hawk]]s (''Accipiter striatus'') or [[zone-tailed hawk]]s (''Buteo albonotatus''), or more open plain and meadow areas, such as [[Northern harrier]]s (''Circus hudsonius'') and ferruginous hawks, but this is almost never a total insurance against predation as all of these are recorded prey.<ref name= Hamerstrom/><ref>Stoleson, S. H., & Sadoti, G. (2010). ''Zone-tailed Hawk (Buteo albonotatus)''. In: Cartron, Jean-Luc, ed. Raptors of New Mexico. Albuquerque, NM: University of New Mexico Press.</ref><ref>Sutherland, J. E. 1987. ''The predation ecology of the Northern Harrier (Circus cyaneus hudsonius) on Mallard Island, North Dakota''. Master's Thesis. Univ. of N. Dakota, Grand Forks.</ref><ref>Bechard, Marc J. and Josef K. Schmutz. 1995. ''Ferruginous Hawk (Buteo regalis)'', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.</ref>

In a study of [[red-shouldered hawk]] (''Buteo lineatus'') and [[broad-winged hawk]] (''Buteo brachyurus'') breeding in [[New York (state)|New York]], despite their nesting in deeper woods than those that host these owls, the main cause of nest failure was great horned owl predation.<ref name= Crocoll/> Similarly, the great horned owl was the primary cause of nesting failure for both desert-dwelling [[Harris's hawk]]s (''Parabuteo unicinctus'') and forest-dwelling [[northern goshawk]] in [[Arizona]] (39% and 40% of failures, respectively), wetland-inhabiting [[osprey]] (''Pandion haliaetus'') in [[Delaware]] (21% of failures) and [[peregrine falcon]]s (''Falco peregrinus'') in the [[Western United States]] (27% of failures).<ref>Dawson, J. W., & Mannan, R. W. (1991). ''The role of territoriality in the social organization of Harris' Hawks''. The Auk, 661–672.</ref><ref>Steidl, R. J., & Griffin, C. R. (1991). ''Growth and brood reduction of mid-Atlantic coast ospreys''. The Auk, 363–370.</ref><ref>Walton, B. J., & Thelander, C. G. (1988). ''Peregrine falcon management efforts in California, Oregon, Washington, and Nevada''. Peregrine falcon populations: their management and recovery. The Peregrine Fund, Boise, Idaho, 587–598</ref><ref>Boal, C. W., & Mannan, R. W. (1994). ''Northern goshawk diets in ponderosa pine forests on the Kaibab Plateau''. Studies in Avian Biology, 16, 97–102.</ref> The fact that many of the nests great horned owls use are constructed by accipitrids may lead to localized conflicts, almost always to the detriment of the hawks rather than the owls. While the young of larger diurnal raptors are typically stolen in the night, great horned owls also readily kill large adult raptors both in and out of breeding seasons, including [[osprey]], [[northern goshawk]] and [[rough-legged buzzard]].<ref>Cold, C. W. 1993. ''Adult male osprey killed at nest by Great Horned Owl''. Passenger Pigeon 55:269–270.</ref><ref>Rohner, C. and F. I. Doyle. 1992. ''Food-stressed Great Horned Owl kills adult goshawk: exceptional observation or community process?'' Journal of Raptor Research, 26:261–263.</ref><ref>Bechard, Marc J. and Theodor R. Swem. 2002. ''Rough-legged Hawk (Buteo lagopus)'', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.</ref>

Great horned owls are frequently mobbed by other birds. Most accipitrids will readily mob them, as will falcons. [[Hen harrier]]s, [[northern goshawk]]s, [[Cooper's hawk]]s, [[Harris's hawk]]s, red-tailed hawks, [[Swainson's hawk]]s, [[ferruginous hawk]]s, [[red-shouldered hawk]]s, [[American kestrel]]s, [[peregrine falcon]]s, [[prairie falcon]]s (''Falco mexicanus'') and [[common raven]]s (''Corvus corax'') are among the reported species who have been recorded diving on great horned owls when they discover them.<ref name= Houston/><ref name= Orians/><ref name= Rohner3>Rohner, C., Krebs, C. J., Hunter, D. B., & Currie, D. C. (2000). ''Roost site selection of great horned owls in relation to black fly activity: an anti-parasite behavior? '' The Condor, 102(4), 950–955.</ref><ref>Houston, C. S. and K. A. Wylie. 1985. Peregrine Falcons harass nesting Great Horned Owls. Blue Jay 43:42–43.</ref> In [[Arizona]] and [[Texas]], they may be mobbed by [[Mexican jay]]s and [[western scrub jay]]s (''Aphelocoma wollweberi & californica'') and [[Western kingbird|western]] and [[Cassin's kingbird]]s (''Tyrannus verticalis & vociferans'').<ref>Cully, J. F., & Ligon, J. D. (1976). ''Comparative mobbing behavior of scrub and Mexican jays''. The Auk, 116–125.</ref><ref>Ohlendorf, H. M. (1974). ''Competitive relationships among kingbirds (Tyrannus) in trans-Pecos Texas''. Wilson Bulletin, 86(4), 357–373.</ref> In addition, there are several documented incidences of [[American crow]]s mobbing a great horned owl, in groups of dozens or even hundreds of crows.<ref name= Bent/> In response to mobbing, if the owl flies it alights to the nearest secluded spot. If an owl alights on ground or on exposed branch or ledge, it may respond to swooping and stooping flights of corvids and raptors with threat display and raising of its wings.<ref name= Houston/>

==Reproduction==
[[File:Great horned owl chick 3w.jpg|thumb|left|Nestlings of the Rocky Mountains great horned owl (''B. v. pinorum'') in [[New Mexico]]]]
[[File:Bubo virginianus -near Tule Lake National Wildlife Refuge, Oregan, USA -juvenile-8.jpg|right|thumb|Juvenile coastal great horned owls (''B. v. saturatus'') near [[Tule Lake National Wildlife Refuge]], Oregon, United States]]
Great horned owls are some of the earliest-breeding birds in North America, seemingly in part because of the lengthy nightfall at this time of year and additionally the competitive advantage it gives the owl over other raptors. In most of North America, courtship is from October to December and mates are chosen by December to January.<ref name=Konig/> This species was once thought to be strictly monogamous, but recent analysis indicates one male may mate with two females simultaneously, as was discovered for the first time in 2018 in Reno, Nevada.<ref>{{cite web | url=https://www.nationalgeographic.com/animals/article/animals-owls-birds-parenting-polygamy | archive-url=https://web.archive.org/web/20180503042406/https://news.nationalgeographic.com/2018/04/animals-owls-birds-parenting-polygamy/#close | archive-date=May 3, 2018 | title=These Owl Chicks Have Two Moms and a Dad – a First| website=[[National Geographic Society]] | date=2018-05-02}}</ref> 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.<ref name= Konig/> The white throat may serve as a visual stimulus in the low light conditions typical of when this owl courts.<ref name= Rohner/> He often flies up and down on a perch, while approaching the potential mate. Eventually, he comes to approach the female and tries to rub his bill against hers while repeatedly bowing. If receptive, the female hoots back when the pair meet but is more subdued in both her hoot and display. The male may convince the female by bringing her freshly caught prey, which they will share.<ref name=Bent/><ref name= Konig/> While males often hoot emphatically for about a month or six weeks towards the end of the year, the period where females also hoot is usually only a week to ten days.<ref name= Baumgartner/> Pairs typically breed together year after year and may mate for life, although they associate with each other more loosely when their young become mostly independent.<ref name= Konig/> Pairs rekindling their reproductive relationship in the winter may perform a milder courtship to strengthen pair bonds before producing young.<ref name= Baumgartner/>

Males select nesting sites and bring the females' attention to them by flying to the nest and then stomping on it.<ref name=Konig/> Considering the owls' large size, nests with open access are preferred to those enclosed with surrounding branches. Like all owls, great horned owls do not build their own nest. Great horned owls tend to examine an area for an abandoned nest, generally from larger birds like hawks, and take over the nest for raising their own young.<ref>{{Cite journal|last=Morse|first=Douglass H.|date=April 1971|title=Great Horned Owls and Nesting Seabirds|journal=The Auk|volume=88|issue=2|pages=426–427|doi=10.2307/4083889|jstor=4083889|issn=0004-8038}}</ref> They nest in a wider variety of sites than any other North American bird.<ref name= Baumgartner/> Many nests are in cavernous hollows of dead trees or their branches, and especially in southern states in large trees along the edge of old-growth lots.<ref name= Baumgartner/> In mountainous or hilly areas, especially in canyons of the [[Southwestern United States|Southwest]] and [[Rocky Mountains]], cliff ledges, small caves, and other sheltered depressions may be used.<ref name= Baumgartner/> Owls living in prairie country, in the absence of other animals' nests, riparian tree-hollows or man-made structures, will use boulders, buttes, railroad cuts, low bushes and even the bare ground as nest sites.<ref name= Baumgartner/> Ground nests have also been recorded in the midst of tall grasses in [[Florida]] and in the midst of brushy spots on desert ground.<ref name= Voous/> Even the burrow entrances of [[American badger]] and [[coyote]] dens have reportedly been used as nests, in spite of the inherent risk of sharing space with such potentially dangerous co-inhabitants.<ref name= Baumgartner/> Nesting behavior for the great horned owl appears to be more closely related to prey availability than it does to seasonal conditions. There has been some evidence that if prey availability is low enough then the species may forgo mating entirely for a season. Male and female owls of the species have been observed to help incubate the eggs once they have been laid on a nest.<ref>{{Cite web|url=https://greathornedowl.net/great-horned-owl-nest/|title=Great Horned Owl Nest – Interesting Facts & Information|last=Waleed |date=2018-08-29|website=Great Horned Owl|language=en-US|access-date=2020-02-21}}</ref>

[[File:Bubo virginianus00.jpg|thumb|right|A brooding female common great horned owl (''B. v. virginianus'') on her nest in [[Louisiana]]]]
Most tree nests used by great horned owls are constructed by other animals, often from a height of about {{convert|4.5|to|22|m|ft|abbr=on}} off the ground. They often take over a nest used by some other large bird, sometimes adding feathers to line the nest but usually not much more. Allegedly there have some cases where the owls have reinforced a nest structure or appeared to have reconstructed a nest, but as a rule no owl species has ever been known to actually build a nest.<ref name= Baumgartner/> Great horned owls in the Southwest may also use nests in [[Cactus|cacti]], built by [[Harris's hawk]] and red-tailed hawk, as well as large hollows in cacti.<ref>Mader, W. J. 1973. ''Notes on nesting Great Horned Owls in southern Arizona''. Raptor Research, 7:109–111.</ref> The nests they use are often made by most larger types of acciptrids, from species as small as [[Cooper's hawk]]s to [[bald eagle]] and golden eagle, though perhaps most often those of red-tailed hawks and other [[Buteoninae|buteonines]]. Secondly in popularity are [[crow]] and [[raven]] (''Corvus'' ssp.) nests. Even [[Canada goose]], [[black-crowned night heron]] (''Nycticorax nycticorax'') and [[great blue heron]] nests have been used, the latter sometimes right in the midst of an active [[heronry]].<ref>Bendire, C. E. 1892. ''Life histories of North American birds with special reference to their breeding habits and eggs''. Smithsonian Contributions to Knowledge 28:376–389.</ref><ref>Burkholder, G. & Smith, D.G. 1988. ''Great Horned Owl (Bubo virginianus) nesting in a Great Blue Heron (Ardea herodias) heronry''. Journal of Raptor Research, 22 (2): 62.</ref> The leaf nests of [[squirrel]]s are also regularly used but in general great horned owls are partial to stick nests since they provide a much firmer, safer foundation.<ref name= Houston/>

The stage at which eggs are laid is variable across North America. In [[Southern Florida]], eggs may be laid as early as late November to as late as early January. In the [[Southeastern United States|southeast]], from south [[Texas]] to [[Georgia (U.S. state)|Georgia]], egg laying may begin from late December to early February. From [[Southern California]] to northern [[Louisiana]], egg laying is from early February to late March. The largest swath of egg-laying owls from central California to [[South Carolina]] to as far north as [[Ohio]] and [[Massachusetts]] is from late February to early April. In the [[Rocky Mountains]], [[Northwestern United States]], northern [[New England]] and eastern Canada, egg laying is from early March to late April. In the rest of Canada and Alaska, egg laying may be from late March to early May.<ref name= Baumgartner/> The latest known date of egg laying was in mid-June in [[Saskatchewan]] and the [[Yukon Territory]].<ref>Smith, D. G. 1969. ''Nesting ecology of the Great Horned Owl, Bubo virginianus''. Brigham Young University Science Bulletin Biological Services, 10(4):16–25.</ref> In northwestern [[Utah]] and north-central [[Alberta]], egg-laying can be 3–4 weeks earlier than usual when food is abundant and weather is favorable.<ref name= Houston/> For owls found in more tropical climates, the dates of the breeding season are somewhat undefined.<ref name= Konig/> There are usually 2 eggs per clutch, but clutches range in size from 1 to 6 eggs (over 3 is uncommon, over 4 is very rare), depending on environmental conditions.<ref>Austing, G. R. 1968. ''The owls and I''. Audubon 70:72–79.</ref><ref>Peck, G. K. and R. D. James. 1983. ''Breeding birds of Ontario: nidiology and distribution''. Vol. 1. Royal Ontario Museum, Toronto.</ref> The average egg width is {{convert|46.5|mm|in|abbr=on}}, the average length is {{convert|55|mm|in|abbr=on}} and the average weight is {{convert|51|g|oz|abbr=on}}, although mass could be slightly higher elsewhere because this figure is from [[Los Angeles County]], [[California|CA]] where the owls are relatively small.<ref name= Turner>Turner, Jr., J. C. and L. McClanahan, Jr. 1981. ''Physiogenesis of endothermy and its relation to growth in the Great Horned Owl, Bubo virginianus''. Compilation of Biochemical Physiology, 68A:167–173.</ref> The incubation period ranges from 28 to 37 days, averaging 33 days.<ref name= Hoffmeister>Hoffmeister, D. F. and H. W. Setzer. 1947. ''The postnatal development of two broods of Great Horned Owls (Bubo virginianus)''. University of Kansas Publishing Museum of Natural History, 1:157–173.</ref> The female alone usually does all the incubation and rarely moves from the nest, while the male owl captures food and brings it to her, with the first nightly food delivery typically occurring soon after dark.<ref name= Houston/>

The young weigh {{convert|34.7|g|oz|abbr=on}} at birth on average and can gain about {{convert|33|g|oz|abbr=on}} a day for the first four weeks of life, with typical weights in the range of {{convert|800|or|1000|g|lb|abbr=on}} by 25–29 days for males and females, respectively.<ref name= Turner/><ref name= Hoffmeister/> When first hatched the young are covered in whitish gray down, with some brownish about the wings. Gradually the soft juvenile downy plumage comes through the down, being typically a cinnamon-buff color, but with variable hues predicting the eventual color of the mature owls. The extent of down gradually diminishes, developing mature-looking plumage by late summer, although many first year birds still have scattered bits of down into autumn. 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.<ref name= Bent/> The nestling owls develop mostly in behavior between two weeks and two months of age, in which time they adapt the ability to defend themselves, grasp foods and climb. Vocally, the young are able to exert weak chips while still in the egg, developing into a raspy chirp shortly after hatching. 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. The earliest competent hooting by juvenile owls is not until January.<ref name= Houston/><ref>Sumner, Jr., E. L. 1934. ''The behavior of some young raptorial birds''. University of California, Publication on Zoology, 40:331–362.</ref> Young owls move onto nearby branches at 6 weeks and start to fly about a week later. However, the young are not usually competent fliers until they are about 10 to 12 weeks old.<ref name= Konig/> The age at which the young leave the nest is variable based on the abundance of food.<ref name= Mcinvaille/>

The young birds stay in an area ranging from 13 to 52 ha from the nest into fall, but will usually disperse up to several thousand hectares by the end of fall.<ref name= Dunstan2>Dunstan, T. C. 1970. ''Post-fledging activities of juvenile Great Horned Owls as determined by radio-telemetry''. Ph.D. thesis. University of South Dakota, Vermillion.</ref><ref>Fuller, M. R. 1979. ''Spatiotemporal ecology of four sympatric raptor species''. Ph.D. thesis. University of Minnesota, St. Paul.</ref> The offspring have been seen still begging for food in late October (5 months after leaving the nest) and most do not fully leave their parents territory until right before the parents start to reproduce for the next clutch (usually December to January).<ref>Houston, C.S. 1971. Brood size of Great Horned Owls in Saskachetwan. Bird-Banding, 42:103–105.</ref> Birds may not breed for another year or two, and are often vagrants ("floaters") until they establish their own territories.<ref name=Rohner/> Based on the development of the bursa, great horned owls reach sexual maturity at two years of age.<ref>Weller, M. W. 1965. ''Bursa regression, gonad cycle and molt of the Great Horned Owl''. Bird-Banding 36:102–112.</ref>
[[File:Great Horned Owls in Nest.jpg|thumb|left|Adult common great horned owl (''B. v. virginianus'') with juvenile in nest near Madison, Wisconsin]]

===Urban vs rural nesting===
While urban and rural populations show little difference in productivity, there are differences in nest selection.<ref name=":2">{{Cite journal|last=Smith|first=D.|date=1999|title=Nest Site Selection by Urban and Rural Great Horned Owls in the Northeast (Selección del Lugar de Anidamiento por Parte de Bubo Virginianus en Zonas Urbanas y Rurales del Nordeste de los Estados Unidos)|journal=Journal of Field Ornithology|volume=70|issue=4|pages=535–542|jstor=4514446}}</ref><ref>{{Cite journal|last=Minor, William, Minor, Maureen & Ingraldi, Michael|date=1993|title=Nesting of Red-Tailed Hawks and Great Horned Owls in a Central New York Urban/Suburban Area (Anidamiento de Buteo jamaicensis y de Bubo virginianus en un area urbana/suburbana de la parte central de New York|journal=Journal of Field Ornithology|volume=4|issue=4|pages=433–439|jstor=4513852}}</ref>  Rural owls use old [[Bird of prey|raptor]] nests more frequently than urban birds, who utilize crow or squirrel nests. Additionally, urban nesting individuals utilize trees that are taller/wider in diameter and nest much higher compared to rural nesting Great Horned Owls. The reason behind this increased tree height is due to the fact that urban areas have large trees used for ornamentation, shade and shelter. The higher nesting within the taller trees was attributed to human avoidance. Both rural and urban nesting sites were often within range of paved roads, likely a result of the great horned owl's tendency to hunt along roadways<ref name=":2" />

Studies have shown that nesting in urban areas can influence adult great horned owls to lay eggs earlier than those who nest in rural areas. 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.<ref name=":4">{{Cite journal|last=Stout|first=William E.|date=2008|title=Early breeding records and nesting phenology of Great Horned Owls in Wisconsin.|url=https://www.researchgate.net/publication/318641979|journal=The Passer Pigeon|volume=70|pages=381–388}}</ref> Nesting owls at sites in [[Winnipeg|Winnipeg, Manitoba]] began nesting five to six weeks earlier than those in rural parts of Manitoba, presumably due to experiencing an extremely warm winter by Winnipeg's standards, as well as benefitting from the local [[urban heat island]].<ref name=":5">{{Cite journal|last=Artuso|first=Christian|date=2007-03-01|title=January initiation of suburban great horned owl nests in Manitoba|url=https://bluejayjournal.ca/index.php/bluejay/article/view/5871|journal=Blue Jay|language=en|volume=65|issue=1|doi=10.29173/bluejay5871|issn=2562-5667|doi-access=free}}</ref>

==Mortality and longevity==

===Longevity and natural mortality===
Great horned owls seem to be the most long-lived owl in North America. Among all owls, they may outrank even the larger Eurasian eagle owl in known longevity records from the wild,<ref name= Voous/> with almost 29 years being the highest age for an owl recorded in North America.<ref>Nero, R. W. 1992. ''New Great Horned Owl longevity record''. Blue Jay 50:91–92.</ref> In captivity, the record for the longest lived great horned owl was 50 years.<ref>{{Cite web|url=https://www.visitbigsky.com/blog/interesting-facts-about-great-horned-owls-1/|title=Interesting Facts About Great Horned Owls|last=Sky|first=Big|date=2016-10-10|website=Visit Big Sky, Montana|language=en-US|access-date=2020-02-21|archive-date=2020-02-21|archive-url=https://web.archive.org/web/20200221212624/https://www.visitbigsky.com/blog/interesting-facts-about-great-horned-owls-1/}}</ref> A more typical top lifespan of a great horned owl is approximately 13 years.<ref name= Mikkola/> In general, great horned owls are most vulnerable in the early stages of life, although few species press attacks on the owl's nests due to the ferocious defensive abilities of the parents. Occasionally, nestlings and fledglings will fall from the nest too early to escape or to competently defend themselves and fall prey to [[fox]]es, [[bobcat]], [[coyote]]s, or wild or feral [[cat]]s. Occasionally [[raccoon]]s and [[American black bear]]s consume eggs and nestlings from tree nests and [[Virginia opossum]] may take the rare unguarded egg.<ref name= Voous/><ref name= Houston/> [[Crow]]s and [[raven]]s have been reported eating eggs and small nestlings. This can normally only happen when owls are driven from the nest by human activity or are forced to leave the nest to forage by low food resources but on occasion huge flocks of crows have been able to displace owls by harassing them endlessly.<ref name= Bent/><ref name= Houston/> In general, great horned owls rarely engage in [[siblicide]], unlike many other raptorial birds. Siblicide occurred at 9 of 2,711 nests in [[Saskatchewan]].<ref name= Houston2/> Most cases where young owls are killed and/or consumed by their siblings or parents appear to occur when the nestling is diseased, impaired or starving or is inadvertently crushed.<ref name= Hamerstrom/> Adults generally have no natural predators, excepting both North American [[eagle]]s and other owls of their own species.<ref name= Bent/>

Occasionally, great horned owls may be killed by their own prey. Although typically able to kill skunks without ill effect, five owls were found blind after getting sprayed in their eyes by skunks.<ref>Garcelon, D. K. 1981. ''Mortality of Great Horned Owls associated with skunks''. Murrelet 62:26.</ref> Cases where the quills of porcupines have killed or functionally disabled them have been observed as well.<ref name= Powell/> Violent fights have been observed between great horned owls after attempts to capture [[Western rat snake|rat snake]]s and [[Coluber constrictor|black racers]].<ref name= Bent/><ref>Peterson, R. T. 1968. ''The Birds''. Time-Life International (Nederland).</ref><ref>Perry, R. W., Brown, R. E., & Rudolph, D. C. (2001). ''Mutual mortality of great horned owl and southern black racer: a potential risk of raptors preying on snakes''. The Wilson Bulletin, 113(3), 345–347.</ref> 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.<ref name= Herbert>Herbert, R. A., & Herbert, K. G. S. (1965). ''Behavior of peregrine falcons in the New York City region''. The Auk, 62–94.</ref> During their initial dispersal in fall, juvenile owls have a high mortality rate, frequently more than 50%.<ref name= Houston/> For owls in the [[Yukon Territory]], juvenile survival in the 9 weeks after dispersal has dropped from 80% to 23.2% in a span of three years in response of instability of food supply. In the Yukon, adults on territory had an average annual survival rate of 90.5%.<ref name= Rohner/> Anemia, caused by ''[[Leucocytozoon|Leucocytozoon ziemanni]]'' and the drinking of blood by swarming, blood-drinking [[Simulium|blackflies]] (''Simulium'' ssp.), was a leading cause of juvenile mortality in the Yukon.<ref name= Rohner2/>

===Human-related mortality===
The great horned owl is not considered a globally threatened species by the [[IUCN]].<ref name=IUCN/> Including the Magellanic species, there are approximately 5.3 million wild horned owls in the Americas.<ref name= Mikkola/> Most mortality in modern times is human-related, caused by owls flying into man-made objects, including buildings, cars, power lines, or barbed wire.<ref name= Houston/> In one study, the leading causes of death for owls were collision with cars, entanglement with wires, flying into buildings and, lastly, electrocution.<ref>Stewart, P. A. (1969). ''Movements, population fluctuations, and mortality among great horned owls''. The Wilson Bulletin, 155–162.</ref> Among 209 banded nestlings in yet another study, 67% were found dead after independence: 56 were found shot, 41 were trapped, 15 hit by cars, 14 found dead on highways and 14 electrocuted by overhead power lines.<ref>Olendorff, R. R., Miller, A. D., & Lehman, R. N. (1981). ''Suggested practices for raptor protection on powerlines: the state of the art in 1981 (No. 4)''. Published and distributed for the Edison Electric Institute by Raptor Research Foundation.</ref> 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.<ref>Mendenhall, V. M. and L. F. Pank. 1980. ''Secondary poisoning of owls by anticoagulant rodenticides''. Wildlife Society Bulletin, 8:311–315.</ref><ref>Cheney, C. D., S. B. Vander Wall, and R. J. Poehlmann. 1987. ''Effects of strychnine on the behavior of Great Horned Owls and Red-tailed Hawks''. Journal of Raptor Research, 21:103–110.</ref><ref>Seidensticker IV, J. C. and H. V. Reynolds III. 1971. ''The nesting, reproductive performance, and chlorinated hydrocarbon residues in the red-tailed hawk and Great Horned Owl in southcentral Montana''. Wilson Bulletin, 83:408–418.</ref><ref>Blus, L. J. 1996. ''Effects of pesticides on owls in North America''. Journal of Raptor Research, 30:198–206.</ref><ref>Buck, J. A., L. W. Brewer, M. J. Hooper, G. P. Cobb, and R. J. Kendall. 1996. ''Monitoring Great Horned Owls for pesticide exposure in southcentral Iowa''. Journal of Wildlife Management, 60:321–331.</ref><ref>Keith, J. A. and I. M. Gruchy. 1972. ''Residue levels of chemical pollutants in North American birdlife''. Proceedings of International Congregation of Ornithology, 15:437–452.</ref>

Frequently, the species were denominated a pest due to the perceived threat it posed to domestic fowl and potentially small game. The first genuine nature conservationists, while campaigning against the "Extermination Being Waged Against the Hawks and Owls", continued to advocate the destruction of great horned owls due to their predatory effect on other wildlife.<ref name= Voous/> Thus, small bounties were offered in trade for owl bodies. Around the turn of the 20th century, the great horned owl was considered endangered in the state of [[Michigan]] because of the large number of poachers who were illegally hunting and collecting it.<ref>Barrows, W. B. 1912. "Michigan bird life". Michigan Agricultural College, Lansing.</ref> Hunting and trapping of great horned owls may continue on a small scale but is now illegal in most countries.

===Effect on conservation-dependent species===
Occasionally, these owls may prey on threatened species. Following the devastation to its populations from [[DDT]], the reintroduction of the [[peregrine falcon]] to the [[Mississippi River|Mississippi]] and [[Hudson River]]s was hampered by great horned owls killing both young and adult peregrines at night.<ref>Cade, T. J., P. T. Redig, and H. B. Tordoff. 1989. ''Peregrine Falcon restoration: Expectation vs. reality''. Loon 61:160–162.</ref> Similarly, as mainly recorded in [[New England]], attempts to reintroduce [[osprey]]s, after they were also hit hard by DDT, were affected by heavy owl predation on nestlings, and the owls were also recorded to take a large toll locally on the threatened colonies of [[roseate tern]]s.<ref name= Houston/> Where clear-cutting occurs in old-growth areas of the [[Pacific Northwest]], spotted owls have been badly affected by considerable great horned owl predation.<ref name= Johnson2/><ref>Forsman, E. D., E. C. Meslow, and H. M. Wight. 1984. ''Distribution and biology of the Spotted Owl in Oregon''. Wildlife Monographs, 87.</ref> 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 squirrel]]s (''Urocitellus townsendii''),<ref name="Marti, C. D. 1996"/> [[Pacific pocket mice]] (''Perognathus pacificus''),<ref>Brylski, P., Hays, L., & Avery, J. (1998). ''Recovery Plan for the Pacific Pocket Mouse, Perognathus longimembris pacificus''. U.S. Fish & Wildlife Service.</ref> [[giant kangaroo rat]]s,<ref>Grinnell, J. (1932). ''Habitat relations of the giant kangaroo rat''. Journal of Mammalogy, 13(4), 305–320.</ref> [[Stephens' kangaroo rat]] (''Dipodomys stephensi''),<ref>Kelt, D. A., Wilson, J. A., & Konno, E. S. (2005). ''Differential response of two kangaroo rats (Dipodomys) to the 1997–1998 El Niño southern oscillation event''. Journal of Mammalogy, 86(2), 265–274.</ref> [[black-footed ferret]]s,<ref>Breck, S. W., Biggins, D. E., Livieri, T. M., Matchett, M. R., & Kopcso, V. (2006). ''Does Predator Management Enhance Survival of Reintroduced Black-footed Ferrets? '' Recovery of the black-footed ferret-progress and continuing challenges, 203–209.</ref> [[Greater prairie-chicken|greater]] and [[lesser prairie-chicken]]s,<ref>Berger, D. D., Hamerstrom, F., & Hamerstrom Jr, F. N. (1963). ''The effect of raptors on prairie chickens on booming grounds''. The Journal of Wildlife Management, 778–791.</ref><ref>Hagen, C. A., Pitman, J. C., Sandercock, B. K., Robel, R. J., & Applegate, R. D. (2007). ''Age‐Specific Survival and Probable Causes of Mortality in Female Lesser Prairie‐Chickens''. The Journal of wildlife management, 71(2), 518–525.</ref> [[marbled murrelet]]s (''Brachyramphus marmoratus''),<ref>Nelson, S. K., & Hamer, T. E. (1995). ''Nest success and the effects of predation on marbled murrelets''. Ecology and Conservation of the Marbled Murrelet. USDA Forest Service General Technical Report PSW-GTR-152. Pacific Southwest Research Station, Albany, CA, 89–98.</ref> [[ivory-billed woodpecker]]s, [[Florida scrub jay]]s (''Aphelocoma coerulescens''),<ref>Woolfenden, Glen E. and John W. Fitzpatrick. 1996. ''Florida Scrub-Jay (Aphelocoma coerulescens) '', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology</ref> [[pinyon jay]]s,<ref>Balda, R. P., & Bateman, G. C. (1971). ''Flocking and annual cycle of the pinon jay, Gymnorhinus cyanocephalus''. Condor, 287–302.</ref> [[Kirtland's warbler]]s (''Setophaga kirtlandii'')<ref>Mayfield, Harold F. 1992. ''Kirtland's Warbler (Setophaga kirtlandii)'', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology</ref> and [[rusty blackbird]]s (''Euphagus carolinus'').<ref name= Errington2/> The [[American Bird Conservancy]]'s "green list" includes birds with considerable population declines (many classed as [[near threatened]] by the [[IUCN]]) or other immediate threats and/or restricted populations. Altogether, great horned owls hunt 50 different species from that list.<ref name= Voous/><ref>Chipley, R.M., Fenwick, G.H., Parr, M.J. & Pashley, D.M., editors, 2003. ''The American Bird Conservancy Guide to the 500 Most Important Bird Areas in the United States: Key Sites for Birds and Birding in All 50 States''. Random House Trade Paperbacks, {{ISBN|0812970365}}.</ref>

==Captivity==
From experimentally raising young owls in captivity, [[:de:Paul Errington|Paul L. Errington]] felt that they were a bird of "essentially low intelligence" that could only hunt when partially wild and instinctually driven by hunger to hunt whatever they first encounter. He showed captive birds that were provided strips of meat from hatching, rather than having to hunt or to simulate hunting to obtain food, had no capacity to hunt.<ref name= Errington>{{cite journal |last1=Errington |first1=P.L. |year=1932 |title=Studies on the Behavior of the Great Horned Owl |journal=Wilson Bulletin |volume=44 |issue=4 |pages=212–220 |url=https://sora.unm.edu/node/125642}}</ref> On the contrary, William J. Baerg compared behaviorally his captive-raised great horned owls to [[parrot]]s, 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."<ref name= Baerg>{{cite journal |last1=Baerg |first1=W. J. |year=1926 |title=Trying to Tame a Great Horned Owl |journal=The Auk |volume=43 |issue=2 |pages=214–217 |doi=10.2307/4074915|jstor=4074915 }}</ref> Carl D. Marti disagrees with Errington's assessments, noting that their prey selection is not as "completely random as Errington suggested". He further notes that though great horned owls appear to "select their mammalian prey in general relation to the prey populations", [[Cottontail rabbit|cottontail]]s seem to be selected as prey "out of relation to their population status".<ref name="Marti" /><ref name="Errington" />

Arthur C. Bent also noted the variability in temperaments of great horned owls to their handlers, some generally pleasant, though most are eventually aggressive.<ref name="Bent" /> Most captive specimens, once mature, seem to resent attempts at contact and are often given to attacking their keepers. 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.<ref name="Errington" /><ref name="Baerg" /> 

A male great horned owl and a female Eurasian eagle-owl produced an apparently healthy [[hybrid (biology)|hybrid]] young at [[Dudley Zoo]] in England.<ref>{{cite journal |last1=Risdon |first1=D.H.S. |year=1951 |title=The rearing of a hybrid Virginian x European Eagle-Owl at Dudley Zoo |journal=Avicultural Magazine |volume=57 |pages=199–201 |url=https://archive.org/details/avicultur565719501951asco/mode/2up?view=theater}}</ref> 

==Iconography and myth==
Many warrior-based tribes of [[Native Americans in the United States|Native Americans]] admired the great horned owl for their "strength, courage and beauty".<ref name=DwightSmith/> The [[Pima people|Pima]] of the [[Southwestern United States|Southwest]] believed that owls were reincarnations of slain warriors who fly about by night. The [[Arikara]] of the [[Great Plains]] had mystic owl societies in which initiates were made to adorn a facial mask made of the wing and tail feathers of great horned owls. Some Native American nations regarded the great horned owl as a friendly spirit that could aid in matters of love, such as the [[Passamaquoddy]] of [[Maine]], who felt the call of this species was a magical love flute designed to ignite human passions. The [[Hopi]] of the [[Southwestern United States|Southwest]] also associated this owl with fertility, albeit of a different kind: they believed the calling of the owls into summer predicted hot weather, which produced good peach crops. During the [[winter solstice]], the Hopi performed a ceremony with great horned owl feathers in hopes of summoning the heat of summer. Tribes in [[New Mexico]] were known to use owl wing-feathers to produce arrows which could strike their enemies with a minimum of sound. The [[Zuni people|Zuni]] held owl feathers in their mouths hoping to gain some of the silence that owls use in ambushes while striking their own enemies from other tribes. The [[Iroquois]] felt the origin of the great horned owl was due to an unformed owl annoying [[Iroquois mythology|Raweno]], the almighty creator, while Raweno created the [[rabbit]], causing Raweno to make the owl "covered with mud" (dark camouflage) and doomed to ceaselessly call "whoo whoo", which he used while harassing Raweno by night because Raweno was active during the day.<ref name=DwightSmith/>

===Provincial bird===

The great horned owl is the [[List of Canadian provincial and territorial symbols|provincial bird]] of [[Alberta]].<ref>{{cite web|title=Great Horned Owl (Bubo virginianus)|url=http://aep.alberta.ca/fish-wildlife/wild-species/birds/owls/great-horned-owl.aspx|website=Alberta Environment & Parks|access-date=2018-01-08|archive-date=2018-03-06|archive-url=https://web.archive.org/web/20180306023249/http://aep.alberta.ca/fish-wildlife/wild-species/birds/owls/great-horned-owl.aspx}}</ref>

==References==
{{Reflist|30em}}

==Further reading==
{{Refbegin}}
* {{cite journal|last=Accordi|first=Iury Almeida|author2=Barcellos, Andre|title=Composição da avifauna em oito áreas úmidas da Bacia Hidrográfica do Lago Guaíba, Rio Grande do Sul|journal=Revista Brasileira de Ornitologia|date=June 2006|volume=14|issue=2|pages=101–115|url=http://www.ararajuba.org.br/sbo/ararajuba/artigos/Volume142/ara142art2.pdf|language=pt, en|archive-url=https://web.archive.org/web/20081219192057/http://www.ararajuba.org.br/sbo/ararajuba/artigos/Volume142/ara142art2.pdf|archive-date=2008-12-19}}
* {{cite journal |last=Banks |first=R.C. |author2=Cicero, C. |author3=Dunn, J.L. |author4=Kratter, A.W. |author5=Ouellet, H. |author6=Rasmussen, P.C. |author7=Remsen, J.V. Jr. |author8=Rising, J.A. |author9=Stotz, D.F. |title=Forty-Second Supplement to the AOU Checklist of North American Birds |journal=The Auk |year=2000 |volume=117 |issue=3 |pages=847–858 |doi=10.1642/0004-8038(2000)117[0847:FSSTTA]2.0.CO;2 |doi-access=free }}
* {{cite journal|last=Dickerman|first=Robert W.|title=The Taxonomy of the Subarctic Great Horned Owl (''Bubo virginianus subarcticus'') Nesting in the United States|journal=The American Midland Naturalist|date=1 July 2002|volume=148|issue=1|pages=198–199|doi=10.1674/0003-0031(2002)148[0198:TTOTSG]2.0.CO;2|s2cid=85988692 }}
* {{cite journal |last=Dickerman |first=Robert W. |title=Notes on the type of ''Bubo virginianus sclariventris'' |journal=[[Bulletin of the British Ornithologists' Club]] |date=29 January 2004 |volume=124 |issue=1 |pages=5–6 |url=http://www.msb.unm.edu/birds/publications/Bubo_virginianus_BBOC.pdf }}
* Ganey, J. L., W. M. Block, J. S. Jenness, R. A. Wilson (1997). "Comparative habitat use of sympatric Mexican spotted and great horned owls." ''J. Wildl. Res.'' '''2'''(2): 115–123.
* 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}}
* 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 2006-12-05. [https://bna.birds.cornell.edu/bna/species/372/articles/introduction (HTML preview)]
* {{cite journal|last=Howard|first=Hildegarde|author-link=Hildegarde Howard|title=A Preliminary Survey of Trends in Avian Evolution From Pleistocene to Recent Time|journal=Condor|year=1947|volume=49|issue=1|pages=10–13|url=http://sora.unm.edu/sites/default/files/journals/condor/v049n01/p0010-p0013.pdf|doi=10.2307/1364422|jstor=1364422}}
* Johnson, D. H. (1993). [http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/36472/JohnsonDavidHarold1993.pdf?sequence=1 "Spotted owls, great horned owls, and forest fragmentation in the central Oregon Cascades."] ''Thesis. Oregon State University, Corvallis, US.''
* Rohner, C. (1997). [http://www.nrs.fs.fed.us/pubs/gtr/gtr_nc190/gtr_nc190_347.pdf "Non-territorial floaters in great horned owls (Bubo virginianus)"] {{Webarchive|url=https://web.archive.org/web/20160222073757/http://www.nrs.fs.fed.us/pubs/gtr/gtr_nc190/gtr_nc190_347.pdf |date=2016-02-22 }}. In: Duncan, JR; Johnson, DH; Nicholls, TH (eds): ''Biology and conservation of owls of the Northern Hemisphere, 2nd International Symposium''. St. Paul, MN: US Department of Agriculture, Forest Service. pp.&nbsp;347–362.
* Rohner, C., and F. I. Doyle (1992). "Food-stressed great horned owl kills adult goshawk: exceptional observation or community process?" ''J. Raptor Res.'' '''26'''(4): 261–63.
* Rohner, Christoph, and Charles J. Krebs (1996). [https://link.springer.com/article/10.1007%2FBF00334655#page-1 "Owl predation on snowshoe hares: consequences of antipredator behaviour."] ''Oecologia'' '''108'''(2): 303–310.
{{Refend}}

==External links==
{{Commons category|Bubo virginianus|the great horned owl}}
{{Wikispecies|Bubo virginianus}}
{{Collier's poster|Virginian Eared Owl}}
* {{InternetBirdCollection|great-horned-owl-bubo-virginianus|Great Horned Owl}}
* [https://web.archive.org/web/20120817075924/http://www-rci.rutgers.edu/~au/owl.htm Information on Owls], a compilation of various sources pertaining to owls
* [https://www.mbr-pwrc.usgs.gov/id/framlst/i3750id.html Great Horned Owl – ''Bubo virginianus''] – USGS Patuxent Bird Identification InfoCenter
* {{VIREO|Great+Horned+Owl|Great Horned Owl}}

{{Taxonbar|from=Q81515}}
{{Authority control}}

[[Category:Bubo (genus)|great]]
[[Category:Owls of the Americas|great horned owl]]
[[Category:Pleistocene birds]]
[[Category:Provincial symbols of Alberta]]
[[Category:Apex predators]]
[[Category:Articles containing video clips]]
[[Category:Birds described in 1788|Great horned owl]]
[[Category:Taxa named by Johann Friedrich Gmelin|Great horned owl]]
[[Category:Extant Pleistocene first appearances]]
[[Category:Birds of Mexico]]