Like other owl species, great horned owls have a rounded face and yellow eyes that face forward. They have a black bill with white or tan feathers surrounding it. They have feathers on top of their heads that look like horns. These are usually darker than the rest of their head, which is important for camouflage. They have a white spot on their throat. Their bellies are white with brown and black stripes and markings on them. Their back is darker in color, with black and brown colors in the feathers. (Dickerman and Johnson, 2008; Dickerman, 1991; McGillivray, 1989; Rohner, 2001)
Great horned owls are are not all the same size. Females are a little bit larger than males. Females weigh 1.7 kg on average and males weigh 1.3 kg on average. Great horned owls in the north are a bit bigger and have a wingspan a little bit longer than great horned owls in the south. In northern latitudes, they tend to have larger core bodies and a longer wingspan. Many other species are larger in the north as well. Great horned owls are 45.7 to 63.5 cm long and their wingspan is 127 to 152.4 cm. Their coloring also changes depending on where they live. A subspecies of great horned owls that lives in forests and meadows is darker and browner than other great horned owls. The area where they live also changes what color they are. Another subspecies in Baja California lives in the desert and is lighter and grayer than other great horned owls. (Dickerman and Johnson, 2008; Dickerman, 1991; McGillivray, 1989; Rohner, 2001)
Great horned owls live on almost all of the continent of North America and down into Central and South America too. They farthest north they live is the northern tip of Alaska, at 68 degrees north latitude. The farthest south they live is at the southern end of Brazil, at 54 degrees south latitude. (McGillivray, 1989; Meiri and Dayan, 2003; Morrell, 1993)
Great horned owls can live in many types of habitats. They can live at sea level along the coast, but they can also live as high as 3352.8 m above sea level. They are often found in habitats that are a mix of woods and open fields. They can live in grasslands, in the desert, and in and around where humans live. They can also live in swamps and marshes and coastal forests as well. (Dickerman and Johnson, 2008; Dickerman, 1991; Morrell, 1993; Rohner, 2001)
Great horned owls form a mating pair to raise their young. They find each other through hooting. Males hoot all year long but females only hoot during the mating season. The mating pair marks a territory that other breeding pairs are not allowed to enter. This is so they don't have to compete with other great horned owl pairs for food within their territory. Compared to other animals, they are not totallyy territorial. They mostly protect the area closest to their nest. (Baumgartner, 1938; Rohner, 2001; Walsh, 1989)
Great horned owls take over nests that were abandoned by squirrels or other birds. Sometimes they take over nests abandoned by other great horned owls. The number of chicks they have depends on where they live and how much food is available that year. If there is not very much food available that year, they have a smaller number of chicks. On the east coast of the United States, they usually don't have more than 2 chicks. In Central America and western North America, it is normal for them to have 3 or 4 chicks. Overall, they have 1 to 6 eggs per season. The eggs hatch in 30 to 37 days. Great horned owl chicks can fly after 6 to 9 days and can be independent of their parents at 5 to 10 weeks. In 1 to 3 years, they are able to have their own chicks. Like other birds that live in so many different places, the ones that live in north nest later than the ones that live in the south. (Baumgartner, 1938; "Great Horned Owl", 2012a; Rohner and Krebs, 1996; Rohner and Smith, 1996)
When the mating pairs of great horned owls are nesting, males and females switch off hunting and protecting the chicks. Males do most of the hunting and females spend most of the time with the chicks. If there is not a lot of food around, females more often leave the nest to look for more food. This also happens if there are a lot of chicks. Great horned owls have nests in different locations depending on their habitat. In older forests their nests can be up to 100 feet off the ground. In prairies or grasslands they nest in bushes, small sheltered areas in cliffs, or even on the ground. (Baumgartner, 1938; Rohner and Smith, 1996)
Great horned owls live an average of 13 years in the wild and 20 years in captivity. The record for the longest life in the wild is 28 years old. The record for the longest life in captivity is 35 years. Human activities can destroy their habitat and make them less likely to live as long. (Rohner, 2001; Rudolph, 1970; Sullivan, 1995)
Great horned owls live by themselves most of the time, except when they are nesting. They usually stay near the same area and do not migrate like many other birds do. They communicate with each other by hooting. Most of the time hooting is used to decide the boundaries of their territory. If there is a disagreement over their territory, it can sometimes end in death. Other times, certain great horned owls that do not have a mate or a territory travel between the territories of other great horned owls. They avoid disagreements by not hooting and staying at the edges of the territory they are inside of. (Baumgartner, 1938; Dickerman and Johnson, 2008; Houston, et al., 1998; Kinstler, 2009; Rohner, 2001)
Great horned owls have home ranges of different sizes. They are territorial, but sometimes they only defend the part of their territory that is closest to the nest. Their territories are 5.26 to 5.56 sq km in area. (Rohner, 2001; Walsh, 1989)
Great horned owls communicate with each other by hooting. Hooting establishes their territories and also is used to find mates. When hooting to mark their territory, they sound like, "hoo-hoo hoooo hoo-hoo." This sound can be heard from miles away. When they are attacking prey, they screech loudly. Scientists play recordings of great horned owls hooting and then listen for their response to figure out how many of them live in a particular area. Great horned owls have great vision which allows them to see their prey and find their way through the darkness, even in the forest. They have binocular vision, which means they have excellent vision facing forward but their vision on the sides is weaker. They can lose their vision from accidents, infections, and maybe from problems with their genes. (Fite, 1973; Kinstler, 2009; Maclaren, et al., 1995; Rohner, 2001; Walsh, 1989)
Great horned owls are carnivores. They usually eat animals that live on land and have backbones. Their diet depends on what kind of prey is available. If they are living in older forests, they usually eat rabbits and hares, pikas, and voles. In the southwestern U.S., great horned owls eat young rabbits and small rodents and also insects. If they are living in fields and deserts, they usually eat rodents and insects. If they are living near water, they also eat fish, amphibians, crustaceans, and reptiles. Great horned owls hunt by perching on a branch and searching for prey. When the see their prey, they swoop down from the branch and can catch prey while flying if needed. (Donázar, et al., 1989; Link, 2012; "Great Horned Owl", 2012a)
Great horned owls are at the very top of many food chains, so they do not have natural predators. However, they can sometimes kill each other in a disagreement over territory. Also, crows or raccoons sometimes find and eat their eggs. (Hunter, et al., 1997; "Great Horned Owl", 2012a; Rohner, et al., 2000; Rohner, 2001)
Great horned give birth to more young in years when there is plenty of food. For example, great horned owls in the north eat mostly snowshoe hares <<Lepus americanus>>. When there are a lot of snowshoe hares, the number of great horned owls increases. When there are not as many snowshoe hares, there are not as many great horned owls either. (Rohner, et al., 2000; Rusch, et al., 1972)
Great horned owls can become infected by some parasites. If they are bitten by an infected blackfly, they can become infected with avian malaria. The infection does not always kill them, however. Great horned owls that live where there are blackflies move their nests to avoid them. In the summer when blackflies are biting, they roost on or near the ground. In the winter, when there are fewer blackflies biting, they return to nest in the tops of trees in the forest. (Rohner, et al., 2000; Rusch, et al., 1972)
Great horned owls sometimes eat chicken, ducks, or other poultry raised by humans. ("Great Horned Owl", 2012b)
Great horned owls eat many kinds of animals, including rodents and insects that humans consider pests. They can live in ecosystems were humans live, so they can control the number of rodents and insects. (Donázar, et al., 1989; Rusch, et al., 1972)
Great horned owls are not threatened or endangered. They can live in many kinds of environments and their numbers are not threatened.
Drew Dietrich (author), Radford University, Karen Powers (editor), Radford University, Kiersten Newtoff (editor), Radford University, Melissa Whistleman (editor), Radford University, Catherine Kent (editor), Special Projects.
Minnesota Department of Natural Resources. 2012. "Great Horned Owl" (On-line). Minnesota Department of Natural Resources. Accessed March 18, 2012 at http://www.dnr.state.mn.us/birds/greathornedowl.html.
National Wildlife Federation. 2012. "Great Horned Owl" (On-line). Wildlife Library. Accessed March 31, 2012 at http://www.nwf.org/Wildlife/Wildlife-Library/Birds/Great-Horned-Owl.aspx.
Baumgartner, F. 1938. Courtship and nesting of the great horned owls. The Wilson Bulletin, 50/4: 274-285.
Braekevelt, C. 1993. Fine structure of the pecten oculi in the great horned owl. Histology and Histopathology, 8/1: 9-15.
Brown, R., J. Baumel, R. Klemm. 1994. Anatomy of the propatagium: The great horned owl. Journal of Morphology, 219/2: 205-224.
Cawthorn, R., P. Stockdale. 1982. The developmental cycle of Caryospora bubonis Cawthorn and Stockdale 1981 (Protozoa: Eimeriidae) in the great horned owl, Bubo virginianus (Gmelin). Canadian Journal of Zoology, 60/2: 152-157.
Coefield, S., T. Fredericks, R. Seston, M. Nadeau, D. Tazelaar, D. Kay, J. Newsted, J. Giesy, M. Zwiernik. 2010. Ecological risk assessment of great horned owls (Bubo virginianus) exposed to PCDD/DF in the Tittabawassee river floodplain in Midland, Michigan, USA. Environmental Toxicology and Chemistry, 29/10: 2341-2349.
Dickerman, R. 1991. Specimens from the subarctic nesting population of great horned owl from New York, New Jersey, and Connecticut. The Kingbird, Summer: 154-157. Accessed May 04, 2012 at http://www.msb.unm.edu/birds/publications/Great_Horned_Owl_TK_2.pdf.
Dickerman, R., A. Johnson. 2008. Notes on great horned owls nesting in the Rocky Mountains, with a description of a new subspecies. Journal of Raptor Research, 42/1: 20-28.
Donázar, J., F. Hiraldo, H. Delibes, R. Estrella. 1989. Comparative food habits of the eagle owl Bubo bubo and the great horned owl Bubo virginianus in six palearctic and neartic biomes. Ornis Scandinavica, 20/4: 298-306.
Fite, K. 1973. Anatomical and behavioral correlates of visual acuity in the great horned owl. Vision Research, 13/2: 219-230.
Houston, C. 1975. Reproductive performance of great horned owls in Saskatchewan. Bird Banding, 46/4: 302-304.
Houston, C., D. Smith, C. Rohner. 1998. "Great Horned Owl" (On-line). Birds of North America Online, Cornell Lab of Ornithology. Accessed September 21, 2012 at http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/372/articles/migration.
Hunter, D., C. Rohner, D. Currie. 1997. Mortality in fledgling great horned owls from black fly hematophaga and leucocytozoonosis. Journal of Wildlife Diseases, 33/3: 486-491.
Kinstler, K. 2009. Great horned owl Bubo virginianus vocalizations and associated behaviours. Ardea, 97/4: 413-420.
Link, R. 2012. "Living With Wildlife" (On-line). Accessed April 12, 2012 at http://wdfw.wa.gov/living/owls.html.
Maclaren, N., S. Krohne, R. Porter Jr., M. Ringle, D. Lindley. 1995. Corynenbacterium endophthalmitis, glaucoma, and sceral ossicle osteomyelitis in a great horned owl (Bubo virgininanus). Journal of Zoo and Wildlife Medicine, 26/3: 453-459.
McGillivray, B. 1989. Geographic variation in size and reserve size dimorphism of the great horned owl in North America. The Condor, 91: 777-786.
Meiri, S., T. Dayan. 2003. On the validity of Bergmann's rule. Journal of Biogeography, 30/3: 331-351.
Miller, A. 1934. The vocal apparatus of some North American owls. The Condor, 36/5: 204-213.
Morrell, T. 1993. Status and Habitat Characteristics of the Great Horned Owl in South-Central Pennsylvania. Ann Arbor, MI: Proquest Dissertations and Theses.
Rayment, L., D. Williams. 1997. Glaucoma in a captive-bred great horned owl. The Veterinary Record, 140/18: 481-483.
Rohner, C. 2001. Non-territorial floaters in great horned owls (Bubo virginianus). 2nd Owl Symposium: 347-362.
Rohner, C., C. Krebs. 1996. Owl predation on snowshoe hares: Consequences of Antipredator Behaviour. Oecologia, 108/2: 303-310.
Rohner, C., C. Krebs, B. Hunter, D. Currie. 2000. Roost site selection of great horned owls in relation to black fly activity: An anti-parasite behavior?. The Condor, 102/4: 950-955.
Rohner, C., J. Smith. 1996. Brood size manipulations in great horned owls Bubo virgininanus: Are predators food limited at the peak of prey cycles?. The International Journal of Avian Science, 138/2: 236-242.
Rudolph, S. 1970. Predation ecology of coexisting great horned and barn owls. The Wilson Bulletin, 90/1: 134-137.
Rusch, D., E. Meslow, P. Doerr, L. Keith. 1972. Response of great horned owl populations to changing prey densities. The Journal of Wildlife Management, 36/2: 202-296.
Smith, D. 2002. Great Horned Owl. Mechanicsburg, PA: Stackpole Books.
Sullivan, J. 1995. "Index of Species Information" (On-line). Accessed March 31, 2012 at http://www.fs.fed.us/database/feis/animals/bird/buvi/all.html.
Walsh, D. 1989. Habitat Use, Population Densities, and Vocal Behavior of the Great Horned Owl in Central Utah. Ann Arbor, MI: Proquest Dissertations and Theses.