A great horned owl hunts mostly at night, and this book follows how it lives, from its senses to its food, its nest and the records kept about it. A great horned owl has feather tufts on its head that look like horns, but the tufts are not ears, because they are only tufts of feathers, and it also has a white patch of feathers at its throat, and female great horned owls are larger than males. An adult great horned owl is between 18 and 25 inches long, and its wingspan can reach about 1.5 meters (5 feet), while sources measure its weight in different ways: the Wildlife Science Center says great horned owls generally weigh between 2.2 and 3.8 pounds. The Animal Diversity Web gives an average mass of about 1.7 kg for female great horned owls and 1.3 kg for males. The Owl Research Institute lists adult male great horned owls at 1304 g (2.9 lb) and adult females at 1509 g (3.3 lb). Great horned owls are the largest North American owls with ear tufts.

A great horned owl hunts mostly at night, and it has large eyes, nearly as large as human eyes, that are even larger in proportion to its brain than the eyes of other owls. It has binocular vision, which gives excellent frontal vision but weaker peripheral vision, and its night vision is excellent, in black and white rather than color, and an owl turns its head to look around, because its eyes do not move in the sockets, and an owl can turn its head about 270 degrees, which is three-quarters of the way around a circle. A 2013 Johns Hopkins study of owls found that twelve of the 14 cervical vertebrae, the bones of an owl's neck, have a special adaptation for protecting blood vessels, and in that study the hollow cavities in the neck bones were approximately 10 times larger in diameter than the vertebral artery traveling through them.

In the Audubon account, the comb and fringe of owl wing feathers funnel air smoothly over the wing and dampen the sound, and special flight feathers let an owl fly down silently, and Scott Weidensaul told Audubon that the more nocturnal the owl, the more dependent it is on silent flight, and great horned owls also have soft, fluffy feathers that keep them warm in colder climates. A great horned owl has keen hearing and keen vision in low light, and great horned owls have better depth perception and better perception of sound elevation (up-down direction) than humans, and an owl can pinpoint both the horizontal and vertical direction of a sound, and a great horned owl is keenly attuned to high-frequency sounds, such as those made by squeaky-voiced rodents. A great horned owl watches from a high perch, then swoops down to catch its food, and a great horned owl's hoot is low and deep. You can hear great horned owls hooting at night in winter.

One way to learn what an owl eats is to identify the bony remains of prey in its regurgitated pellets. In a 2005 study of a small sample of great horned owl pellets, feather and hair remains showed three species of birds, while the bones in the pellets represented only mammals. The authors of that study wrote that a pellet finding shows an important bias that challenges the reliability of owl pellet studies using only bones. Up to 90 percent of a great horned owl's diet is mice, voles, squirrels and other small mammals, and great horned owls have the widest prey base of any North American owl. A great horned owl may eat more than 4,000 mice per year, and in the Sierra Nevada, 61 percent of the great horned owl diet consisted of cottontails, as reported in a 1995 U.S. Forest Service review, and to a lesser extent, great horned owls also take reptiles, amphibians, fish and large insects, and they also catch small prey by walking on the ground.

Great horned owls start nesting early, in winter, and great horned owls do not build their own nests, and they add little or no nest material, aside from feathers at times. They use nests built by other large birds, such as hawks and crows, and a great horned owl may also nest on a cliff ledge, in a cave, in a broken-off tree stump, or sometimes on the ground, and in Vermont, great horned owl nests have been found in borrowed hawk and heron nests and in broken tree stubs. In towns and cities, great horned owls nest in deserted buildings and powerline towers, according to a 1995 U.S. Forest Service review, and they use artificial nests when more suitable nest sites are unavailable. A great horned owl usually lays two or three eggs, and published incubation times for great horned owl eggs differ from account to account: 28 to 35 days in one account, 30 to 37 days in another, and 25 to 30 days in a third.

The great horned owl is the most widely distributed true owl in the Americas, and it lives across most of North America. Great horned owls are most commonly found in areas where woodland and open fields are mixed together, and they live in many places, including the countryside and cities. The Peregrine Fund lists the great horned owl's status as Least Concern, as of November 2026, and mated great horned owls stay in their territory all year. The Animal Diversity Web says great horned owl territories are generally 5.26 to 5.56 square kilometers in area, and a 1995 U.S. Forest Service review reported that in southeastern Wisconsin the average annual home range of a great horned owl was about 813 acres (329 hectares). In banding studies, most (93 percent) banded great horned owls from a wide range of study sites were recovered within 48 miles (80 km) of where they were banded. Great horned owls do not regularly migrate, but a 1995 U.S. Forest Service review says it is common for great horned owls to move from Canada to the northern Great Lakes States in winter.

While the female sits on the eggs, the male brings her food, and both parents help feed the young owls, and in a 1995 U.S. Forest Service review, great horned owl nestlings often edged out of the nest by about 32 days, and first flight could occur by 9 weeks, and young great horned owls can fly well at about 9 to 10 weeks old, and parents care for them for up to several months, and a great horned owl usually first breeds at 2 years of age. Much of what scientists know about how long birds live comes from banding data. The record for the longest life in the wild for a great horned owl is 28 years, according to the Animal Diversity Web, as of November 2026, and records of longevity, based on banding, can only go up as more birds are banded and found. Great horned owls in captivity may live more than 20 years.

Words to know

• regurgitated: coughed up
• incubation: egg-sitting time
• banding: tagging with rings
• cervical: of the neck
• longevity: length of life