Great horned owl (GHOW) vary in color from brown to gray, with a wingspan of three–five feet. Their name is derived from the tufts of feathers on either side of their head. GHOW have excellent hearing and sharp vision. Their eyes are incapable of rotation; instead, they are able to rotate their heads 270 degrees in a fluid motion. GHOW activity begins at dusk. GHOW may aggressively protect their nest from threats.
Males and females hoot to each other during nesting season, January–February. They are the first bird species to nest in Lake County each year. Although nearly identical in appearance, the male uses a distinctive posture while calling. The male calls from a prominent branch, holding his body horizontally, drooping his wings, cocking his tail slightly, and inflating his white throat patch. Mutual bill rubbing and preening has been noted when the pair is together. The GHOW pair maintain the same territory for up to eight years, remaining solitary during most of the year, staying with their mate only during the nesting season. The average home range is one square mile.
GHOW do not build a nest of their own, instead they occupy a nest previously built by other large birds, such as red-tailed hawks, American crows and great blue herons. GHOW may also use hollows in trees, clumps of witch's broom, rocky crevices, or artificial platforms. The addition of a few feathers is the only modification the female makes.
Two to four eggs are typically laid. The female sits on the nest constantly during incubation, about 26–35 days. The male perches nearby during this period, bringing food to the female. As the owlets grow the female spends less time on the nest but perches nearby to defend it if threatened.
The owlets are dependent upon their parents for food until the fall, and their harsh begging calls can be heard throughout the summer. They begin roaming from the nest onto nearby branches six–seven weeks after hatching, and cannot fly well until 10–12 weeks of age. Juveniles disperse up to 150 miles from the nest site in the autumn, while adults tend to remain in their breeding areas year-round.