Occasionally, when Great Horned Owls kill more prey than they can eat, they cache the remains for later use. Great Horned Owls will incubate frozen food until it thaws and can be eaten.
Renowned for ferocity, Great Horned Owls kill and eat small to medium mammals of many kinds, especially hares and rabbits. They eat mice, rats, squirrels, opossums, woodchucks, bats, weasels, and the occasional domestic cat. Great-Horned Owls also eat skunks, which are sometimes such a prominent part of the diet that both bird and nest may smell of musk. Although mammalian prey typically comprise more than three quarters of the diet, more than fifty species of birds have been recorded as prey. In addition to hunting small songbirds, Great Horned Owls have been known to eat large birds such as grouse, herons, ducks, Canada Geese, hawks (including Red-tailed), and even other species of owl. A woodland with resident Great Horned Owls usually lacks any other raptors in the immediate vicinity.
In late fall and early winter, the low muffled hooting of a Great Horned Owl may carry great distances, signaling that males are beginning to occupy breeding territories. Males and females sometimes sing duets, the male calling the well-known pattern of four to five hoots, “whoo, whoo-hoo, whooo, whooo.” The female responds with a higher pitched two-syllable call, or six to eight lower pitched hoots, “whoo, whoo-hoo, whoo-oo, whoo-oo.” Although nearly identical in appearance to the female, the male uses a distinctive posture while calling. He calls from a prominent branch or rock, holding his body nearly horizontally, drooping his wings, cocking his tail slightly, and inflating his white throat patch. Once paired, the male and female may roost together in dense foliage or rock crevices.
The development of young Great Horned Owls is prolonged over many months. Typically the female lays two eggs, sometimes more when food is abundant. She uses an old hawk’s nest, crow’s nest, hollow tree, or rock crevice, with the addition of a few feathers as the only improvement. Nesting begins as early as January or February. With such an early start, snowfall may cover the incubating parent and the nest at times. Occasionally the eggs freeze and a new clutch must be laid. After nearly one month, helpless chicks hatch, clad in white, eyes closed. Although the nestlings are unable to fly for ten to twelve weeks, they begin venturing out onto nearby branches after about six weeks. Because fledglings remain dependent on their parents for food until fall, their harsh begging calls may be heard throughout the summer.
The Great Horned Owl is found in a greater variety of habitats than any other owl. It has a vast range, from just south of the Arctic tundra in Canada to the pampas of South America. It inhabits deciduous forests, coniferous forests up to about 11,000 feet, swamps, coastal mangroves, rocky desert canyons, and riverine aspen groves in the Great Plains area. Great Horned Owls in North America reach their highest population densities in eastern Colorado, Nebraska, Kansas, and southern Saskatchewan, where grassland meets forest. They are less common in mountainous regions and in the Mojave and Sonoran Deserts.
Great Horned Owls are one of the largest of North American owls–about the size of a Red-tailed Hawk. They are very bulky with large heads and long ear tufts. They are generally warm brown on the upper parts, spotted with darker brown, black and whitish. The throat is white, contrasting with the darkly splotched upper breast. The brownish-buff underparts are paler toward the belly and barred. The legs and feet are thickly feathered with only the talons exposed. The eyes are large and yellow. Coloration varies both individually and regionally. Birds in the east tend to be more richly colored with orangish facial discs. Those from the far north and desert areas are paler with gray faces. Birds from the far West and from tropical areas are the darkest, with dark reddish facial discs. Sexes are similar, although females tend to be larger and more heavily marked.