They do not build a nest of their own but utilise the nests of other birds such as the hawk, crow and heron. They may also use squirrel nests, hollows in trees, rocky caves, clumps of witches broom, abandoned buildings, or on artificial platforms. They are extremely aggressive when defending its nest and will continue to attack until the intruder is killed or driven off. Normally, two to four eggs are laid and incubated by the female only for 26-35 days. They are fed for another few weeks as they are slowly weaned.
Families remain loosely associated during summer before young disperse in the autumn.
Territories are maintained by the same pair for as many as 8 consecutive years, however, these Owls are solitary in nature, only staying with their mate during the nesting season. A long-lived Owl, captive birds have been known to live 29 to 38 years, and wild Owls up to 13 years. Most mortality is related to man - shootings, traps, road kills and electrocutions. The only natural enemies are other Great Horned Owls and, occasionally, Northern Goshawks during disputes over nest sites. Great Horned Owls have adapted to many different places and climates.