The great horned owl is the most widely distributed true owl in the Americas and one of the continent's most formidable nocturnal predators, ranging from the subarctic forests of Canada to the southern tip of South America [BirdLife 2024; Wikipedia/BotW]. Instantly recognizable by its prominent feathered ear tufts — the "horns" of its name — and a deep, resonant hoot, it is an apex avian predator whose broad diet of more than 500 recorded prey species makes it a keystone regulator of small-mammal populations [Wikipedia/BotW]. Although the species remains widespread and common across its enormous range, it is increasingly exposed to anticoagulant rodenticides that accumulate through its prey, a contamination pathway now well documented across North America [Gomez et al. 2023; Elliott et al. 2022]. This profile examines the owl's biology, its continental range, and the modern pressures that shape its conservation outlook.
Biology and Identification
The great horned owl is a large, heavily built owl with a barrel-shaped body, broad wings, and conspicuous ear tufts. Females are larger than males: across North American populations, males average roughly 1,224 g and females roughly 1,608 g, with total body length spanning about 43–64 cm and wingspan reaching 91–153 cm [Wikipedia/BotW]. Plumage is cryptically mottled in grays, browns, and buff, with a rufous to grayish facial disc bordered in black, a white throat patch, and dense barring on the underparts. The "horns" are tufts of feathers and have no auditory function; the owl's true ears are asymmetrically placed openings on the sides of the head that enable precise localization of prey by sound.
The species is among the most dietary generalists of all raptors. More than 500 prey species have been documented across its range, with mammals comprising the great majority of the diet by frequency and birds forming most of the remainder [Wikipedia/BotW]. Principal prey include rabbits and hares, rats, mice, voles, and ground squirrels; the great horned owl is also one of the few habitual predators of skunks [Wikipedia/BotW; Audubon 2024]. It will take prey as large as geese and other raptors, including smaller owls, and is capable of carrying prey approximately equal to its own body mass [Wikipedia/BotW].
Great horned owls are powerful, largely nocturnal and crepuscular hunters that locate prey by sight and exceptional hearing, striking from a perch with crushing talons. They are among the earliest-nesting birds in North America, frequently laying eggs in late winter — weeks or months ahead of most other raptors — so that fledglings have a long summer to learn to hunt [Audubon 2024]. The species builds no nest of its own, instead reusing the old stick nests of hawks, eagles, crows, and herons, or occupying tree cavities, cliff ledges, caves, and broken snags [Audubon 2024]. Wild individuals commonly live more than a decade, and banded birds have been recorded surviving into their late twenties [ADW 2024].
Habitat and Range
The great horned owl is the most broadly distributed owl in the Americas, breeding from the subarctic treeline of northern Canada and Alaska south through the contiguous United States and Mexico, and discontinuously through Central America into South America as far as Argentina [BirdLife 2024; Wikipedia/BotW]. It is absent from the West Indies and most offshore islands but otherwise occupies a wider array of biomes than almost any other raptor.
The species is a habitat generalist, occurring in deciduous, coniferous, and mixed forests, as well as deserts, prairies, tundra edges, mangrove and riparian woodlands, rocky coasts, mountains, and increasingly urban and suburban landscapes [Wikipedia/BotW; Audubon 2024]. It tends to favor a mosaic of open ground for hunting interspersed with trees or cliffs for nesting and roosting, and is comparatively scarce in unbroken old-growth forest or dense humid rainforest [Wikipedia/BotW]. Its extreme adaptability across climate zones and human-modified habitats underlies its continental abundance.
In accordance with NRWL sensitive-species policy, specific site locations, den or nest sites, and seasonal movement details are not disclosed in this article.
Conservation Status
The great horned owl is listed as Least Concern on the IUCN Red List, most recently assessed in 2018 [BirdLife/IUCN 2018]. The classification reflects the species' extremely large geographic range, very large population, and a population trend assessed as stable; it does not approach the thresholds that would warrant a threatened category under any of the IUCN criteria [BirdLife/IUCN 2018; BirdLife 2024]. Partners in Flight estimates the global breeding population at approximately 5.7 million individuals and assigns the species a low Continental Concern Score [PIF 2024].
The species is listed on CITES Appendix II as part of the order-wide listing of Strigiformes, which places nearly all owls under international trade controls [CITES 2024]. While North American Breeding Bird Survey and Christmas Bird Count data indicate broadly stable continental numbers over recent decades, some regional populations — notably in parts of Canada — have shown localized declines linked to habitat change, contaminants, and collisions [BirdLife 2024]. Historically, even at the height of organochlorine pesticide use, great horned owls did not experience the population crashes or severe eggshell thinning seen in many fish-eating raptors, because their predominantly mammalian prey carried lower contaminant burdens [Sheffield 1997].
Threats
Anticoagulant rodenticides are the most extensively documented contemporary contaminant threat to the species. Because great horned owls prey heavily on rats and other rodents in suburban and agricultural landscapes, they accumulate second-generation anticoagulant rodenticides (SGARs) through secondary poisoning. In a long-term study of birds of prey in western Canada (1988–2018), great horned owls showed an 81% incidence of exposure to at least one SGAR [Elliott et al. 2022]. In a Texas wildlife-rehabilitation dataset, the great horned owl was the most frequently admitted owl, and 21 of 31 individuals tested (67.7%) were positive for anticoagulant rodenticides, with brodifacoum the compound most often detected [Gomez et al. 2023].
Collisions and entrapment with human infrastructure are significant sources of injury and mortality. In the same Texas rehabilitation study, entrapment in human structures and vehicle collisions together accounted for a substantial share of owl admissions with identifiable causes [Gomez et al. 2023]. Vehicle strikes are a recurrent hazard for owls that hunt along roadsides where small mammals concentrate.
Persecution and incidental killing historically reduced numbers where the species was shot as a perceived threat to poultry and game; while now legally protected across much of its range, illegal shooting still occurs. Electrocution on power infrastructure and entanglement also contribute to local mortality.
Habitat alteration affects regional populations unevenly. Although the species tolerates a wide range of modified landscapes, intensive land-use change can reduce prey availability and suitable nesting structures in some areas, contributing to documented regional declines [BirdLife 2024].
What Is Being Done
Legal protection. Across the United States and Canada the great horned owl is protected under the Migratory Bird Treaty Act and equivalent national legislation, prohibiting killing, capture, or trade without authorization. The species' inclusion on CITES Appendix II as part of the order-wide Strigiformes listing subjects international trade to permit controls and monitoring [CITES 2024].
Population monitoring. Long-running continental surveys — the North American Breeding Bird Survey and the Audubon Christmas Bird Count — track the species' distribution and abundance over decades, providing the trend data that underpins its IUCN assessment and flag regional declines for further attention [BirdLife 2024].
Contaminant surveillance and rodenticide reform. Research programs screening raptor tissues for anticoagulant rodenticides have quantified the scale of secondary poisoning in great horned owls and other predators, generating evidence used to advocate for restrictions on the most hazardous second-generation compounds [Elliott et al. 2022; Gomez et al. 2023]. Owls themselves are increasingly used as biomonitors of environmental contamination because their position as top predators integrates exposure across the food web [Sheffield 1997].
Wildlife rehabilitation. Licensed rehabilitation centers treat and release thousands of injured and orphaned raptors annually; rehabilitation admission data have proven a valuable source of information on the causes and frequency of human-related owl mortality [Gomez et al. 2023].
How Readers Can Help
Reduce rodenticide use. The single most direct action for protecting great horned owls is to avoid second-generation anticoagulant rodenticides, which poison owls through the rats and mice they consume. Using snap traps, sealing entry points, and supporting natural rodent control allows owls to do what they do best — suppress rodent populations — without being poisoned [Elliott et al. 2022; Gomez et al. 2023].
Citizen science. Logging owl sightings through platforms such as iNaturalist and eBird, and participating in the Breeding Bird Survey or Christmas Bird Count, contributes directly to the long-term datasets that monitor the species' status [BirdLife 2024].
Drive carefully at dusk and night. Owls hunting along roadsides are vulnerable to vehicle strikes; reducing speed in rural and wooded areas at night lowers collision risk [Gomez et al. 2023].
Support rehabilitation and habitat stewardship. Supporting licensed wildlife rehabilitators, retaining large trees and snags that provide nesting sites, and keeping artificial lighting and disturbance away from known roost areas all help maintain healthy local owl populations.
References
[ADW 2024] Animal Diversity Web. (2024). Bubo virginianus (great horned owl). University of Michigan Museum of Zoology. https://animaldiversity.org/accounts/Bubo_virginianus/
[Audubon 2024] National Audubon Society. (2024). Great Horned Owl (Bubo virginianus) — Audubon Field Guide. https://www.audubon.org/field-guide/bird/great-horned-owl
[BirdLife 2024] BirdLife International. (2024). Species factsheet: Bubo virginianus (Great Horned Owl). https://datazone.birdlife.org/species/factsheet/great-horned-owl-bubo-virginianus
[BirdLife/IUCN 2018] BirdLife International. (2018). Bubo virginianus. The IUCN Red List of Threatened Species 2018: e.T61752071A132039486. https://doi.org/10.2305/IUCN.UK.2018-2.RLTS.T61752071A132039486.en
[CITES 2024] CITES. (2024). Bubo virginianus — listed under Strigiformes spp. (Appendix II). Convention on International Trade in Endangered Species of Wild Fauna and Flora. https://cites.org/eng/taxonomy/term/3315
[Elliott et al. 2022] Elliott, J.E., Silverthorn, V., Hindmarch, S., Lee, S., Bowes, V., Redford, T. & Maisonneuve, F. (2022). Anticoagulant Rodenticide Contamination of Terrestrial Birds of Prey from Western Canada: Patterns and Trends, 1988–2018. Environmental Toxicology and Chemistry, 41(8), 1903–1917. https://doi.org/10.1002/etc.5361
[Gomez et al. 2023] Gomez, E.A., Prestridge, H.L. & Smith, J.A. (2023). Anthropogenic threats to owls: Insights from rehabilitation admittance data and rodenticide screening in Texas. PLOS ONE, 18(8), e0289228. https://doi.org/10.1371/journal.pone.0289228
[PIF 2024] Partners in Flight. (2024). Avian Conservation Assessment Database — Great Horned Owl population estimate and Continental Concern Score (as reported via Cornell Lab of Ornithology, All About Birds). https://www.allaboutbirds.org/guide/Great_Horned_Owl/lifehistory
[Sheffield 1997] Sheffield, S.R. (1997). Owls as biomonitors of environmental contamination. In J.R. Duncan, D.H. Johnson & T.H. Nicholls (Eds.), Biology and Conservation of Owls of the Northern Hemisphere, USDA Forest Service General Technical Report NC-190, pp. 383–398. https://www.nrs.fs.usda.gov/pubs/gtr/gtr_nc190/gtr_nc190_383.pdf
[Wikipedia/BotW] Great horned owl (Bubo virginianus) — natural history compilation drawing on Birds of the World (Cornell Lab of Ornithology) species account. https://en.wikipedia.org/wiki/Great_horned_owl