The Great Horned Owl - large, powerful, and long-lived - is adapted by its anatomy, physiology, and behavior to survive in any climate but arctic-alpine regions. Equally at home in desert, grassland, suburban, and forest habitats, north to the tree line, it has a diverse prey base and the most extensive range with the most variation in nesting sites of any American owl.

Its large eyes are equipped with many rods for night vision and pupils that open widely in the dark. Although its eyes do not move, flexibility in the atlanto-occipital joint enables this owl to swivel its head more than 180° and to look in any direction. Its hearing is acute, assisted by facial disc feathers that direct sound waves to its ears. Its feathers are exceptionally soft, providing superb insulation and allowing for silent flight. Females are able to maintain their eggs at incubating temperature near 37 °C, even when the ambient temperature is more than 70° colder. This species is a perch-and-pounce hunter. Although its short, wide wings allow maneuverability among trees of the forest, the resulting high wing-loading makes aerial foraging less efficient. Its strong talons, which take a force of 13 kg to open, allow it to sever the spinal column of prey even larger than itself. Its hooked beak efficiently tears meat from bones.

Early field studies on the Great Horned Owl focused on territoriality in Kansas ( Baumgartner, F. M. (1939b). Territory and population in the Great Horned Owl. Auk 56:274-282. Close Baumgartner 1939b Baumgartner, F. M. (1939b). Territory and population in the Great Horned Owl. Auk 56:274-282. Close Baumgartner 1939b) and on diet in Iowa and Wisconsin ( Errington, P. L., F. Hamerstrom and Jr. Hamerstrom, F. N. (1940). The Great Horned Owl and its prey in north-central United States. Iowa Agric. Exp. Stn. Res. Bull. 277:757-850. Close Errington et al. 1940). Long-term banding efforts and subsequent analyses of recoveries were made in Saskatchewan ( Houston, C. S. and C. M. Francis. (1995). Survival of Great Horned Owls in relation to the snowshoe hare cycle. Auk 112:44-59. Close Houston and Francis 1995 Houston, C. S. and C. M. Francis. (1995). Survival of Great Horned Owls in relation to the snowshoe hare cycle. Auk 112:44-59. Close Houston and Francis 1995) and Ohio ( Holt, Jr., J. B. (1996b). A banding study of Cincinnati area Great Horned Owls. Journal of Raptor Research 30:194-197. Close Holt 1996b). Major field studies, with an emphasis on breeding biology and diet in relation to predator-prey dynamics, were conducted in Alberta (L. B. Keith and coworkers e.g., Adamcik, R. S., A. W. Todd and L. B. Keith. (1978). Demographic and dietary responses of Great Horned Owls during a snowshoe hare cycle. Canadian Field-Naturalist 92:156-166. Close Adamcik et al. 1978), Wisconsin ( Petersen, L. (1979a). Ecology of Great Horned Owls and Red-tailed Hawks in southeastern Wisconsin. Wis. Dep. Nat. Resour. Tech. Bull. 111. Close Petersen 1979a), and southwestern Yukon Territory (e.g., Rohner, C. (1996). The numerical response of Great Horned Owls to the snowshoe hare cycle: consequences of non-territorial 'floaters' on demography. Journal of Animal Ecology 65:359-370. Close Rohner 1996).