One way to learn what an owl eats is to identify the bony remains of prey in its regurgitated pellets. A great horned owl swallows small prey whole, and it coughs up pellets of the bones and fur it cannot digest. Great horned owls eat rabbits, rats and squirrels, and up to 90 percent of a great horned owl's diet is mice, voles, squirrels and other small mammals. Great horned owls have the widest prey base of any North American owl, and a great horned owl may eat more than 4,000 mice per year. To a lesser extent, they also take reptiles, amphibians, fish and large insects.

A great horned owl has keen hearing and keen vision in low light. A great horned owl 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. An owl turns its head to look around, because its eyes do not move in the sockets, and it can turn its head about 270 degrees, which is three-quarters of the way around a circle. 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. A great horned owl is keenly attuned to high-frequency sounds, such as those made by squeaky-voiced rodents, and special flight feathers let an owl fly down silently.

An adult great horned owl is between 18 and 25 inches long, and an average adult weighs about 3.1 pounds. 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, while 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), and a great horned owl's wingspan can reach about 1.5 meters (5 feet). Great horned owls are the largest North American owls with ear tufts.

Mated great horned owls stay in their territory all year, and the Animal Diversity Web says great horned owl territories are generally 5.26 to 5.56 square kilometers in area. 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). Great horned owls are most commonly found in areas where woodland and open fields are mixed together, and the great horned owl is the most widely distributed true owl in the Americas. 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.

Great horned owls start nesting early, in winter. 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. A great horned owl usually lays two or three eggs, and the eggs hatch in about a month. While the female sits on the eggs, the male brings her food, and both parents help feed the young owls.

Baby great horned owls are covered with down when they hatch. 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. 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. 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. Great horned owls in captivity may live more than 20 years.

Words to know

• regurgitated: coughed up
• binocular: two-eyed
• peripheral: at the sides
• territory: claimed area