Introduction

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 the most extensive range, the widest prey base, and the most variable 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 1939) and on diet in Iowa and Wisconsin (Errington et al. 1940). Long-term banding efforts and subsequent analyses of recoveries were made in Saskatchewan (Houston and Francis 1995) and Ohio (Holt 1996). 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 et al. 1978), Wisconsin (Petersen 1979), and southwestern Yukon Territory (e.g., Rohner 1996).