An opportunistic hunter, the great horned owl has a remarkably varied diet that includes insects, rabbits, hares, opossums, skunks, ducks, geese, herons, reptiles, frogs, fish and occasionally domestic cats (Felis catus) (2) (3) (5) (9). It has also been known to kill animals as large as porcupines (3).
A well-adapted predator, the great horned owl has large eyes which provide it with excellent night vision, making it perfectly suited for hunting at night. Although the eyes are unable to move within the eye socket, the neck of the great horned owl is able to rotate 180 degrees, giving it nearly all-round vision. The acute hearing of this bird enables it to detect its prey and its exceptionally soft feathers prevent it from being detected while flying (2). Hunting at night from an elevated position, the great horned owl is able to see its prey and then attack with its powerful talons. Excess food is stored within the great horned owl’s territory (5).
A generally nocturnal species (3), the great horned owl spends its days roosting in trees, bushes or crevices in cliffs (2) (5). Breeding pairs typically occupy the same territory, which they protect from intruders, becoming especially aggressive and territorial during the breeding season (2) (5). The pair establish and maintain their territory through vocalising (2).
One of the earliest species to begin nesting, the great horned owl begins breeding in late January in certain populations (3). The male and female vocalise together prior to mating, after which a nest is chosen at a suitable site (2) (3) (5). The nesting sites of the great horned owl are extraordinarily variable, and this species occupies a wider range of nest sites than any other bird in the Americas (2).The nest is usually the disused nest of another large bird species, but cavities in trees, cliffs and deserted buildings will also be used, and the great horned owl will also nest on the ground (2) (3) (5).
A single clutch of two eggs is usually laid, although the clutch size occasionally ranges between one and four eggs. The eggs of the great horned owl are dull and white with a slightly rough surface, and are incubated by the female for between 30 and 37 days, with the male feeding the female throughout this period (2).
Once hatched, the nestlings remain in the nest for between 6 and 7 weeks, and begin to fly between 10 and 12 weeks old (2) (5). The nestlings are voracious feeders and weigh around 75 percent of the total adult mass when they leave the nest, after which time they remain within close proximity to the adults until the end of summer or early autumn (2) (3) (5).
The great horned owl is a sedentary species and even the most northerly populations do not migrate (2) (3) (9). However, in times when food becomes scarce, individuals may move to areas where there is more abundant prey (9).