A great horned owl hunts mostly at night. A great horned owl has large eyes, nearly as large as human eyes, that are even larger in proportion to its brain than the eyes of other owls, and 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. A 2013 Johns Hopkins study of owls found that twelve of the 14 cervical vertebrae in an owl's neck have a special adaptation for protecting blood vessels.

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. Scott Weidensaul told Audubon that the more nocturnal the owl, the more dependent it is on silent flight. 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. 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. It watches from a high perch, then swoops down to catch its food, and great horned owls also catch small prey by walking on the ground.

One way to learn what an owl eats is to identify the bony remains of prey in its regurgitated pellets, and a great horned owl coughs up pellets of the bones and fur it cannot digest. In a 2005 study of a small sample of great horned owl pellets, feather and hair remains showed three species of birds. 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, and a great horned owl may eat more than 4,000 mice per year, and to a lesser extent, great horned owls also take reptiles, amphibians, fish and large insects. A great horned owl swallows small prey whole, and great horned owls eat rabbits, rats and squirrels.

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. Great horned owls do not build their own nests, and they use nests built by other large birds, such as hawks and crows, and they add little or no nest material, aside from feathers at times. 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.

Great horned owls start nesting early, in winter, and female great horned owls are larger than males. 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. A great horned owl usually first breeds at 2 years of age.

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 the 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. The same review says it is common for great horned owls to move from Canada to the northern Great Lakes States in winter. Much of what scientists know about how long birds live comes from banding data, and 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 great horned owls in captivity may live more than 20 years.

Words to know

• regurgitated: coughed up
• cervical: of the neck
• vertebrae: neck bones
• banding: tagging with rings
• territory: claimed area