Although we’re deep in winter’s chill, activities that many people associate with spring are underway already. For example, some Great Horned Owls in the Chicago region are beginning to nest.
Great Horned Owls typically are early nesters. Males hoot more in December and early January to court mates. Then mated pairs find nesting locations. They may choose empty tree holes, or move into stick or leaf nests abandoned by squirrels, or large birds, such as hawks. Sometimes the owl pair adds extra materials to line the nest, but often they’ll just use the abandoned nest as is.
Around mid- to late February, the female lays her eggs, about two on average. Then for two and a half months, she spends almost all of her time sitting on the nest. In Great Horned Owls, only females incubate the eggs, but males bring food to their mates while females are sitting on the nest.
Eggs hatch after about a month of incubation. Mother owls brood their young—keep their babies covered—continuously for about two weeks after hatching. As the young grow, the amount of time females spend brooding decreases. Sometime in April, young owls leave the nest (fledge), usually about six to seven weeks after hatching.
Initially after leaving the nest, juvenile owls can fly only short distances, and often just move to nearby branches. But parent birds stay close and defend their young into early autumn. Parents also continue feeding their young, occasionally bringing them prey items to supplement their diets while they learn to hunt.
Why do Great Horned Owls nest so early? One theory is that this timing gives young owls a longer period to learn to hunt before the next winter comes. Hunting is challenging; juvenile owls must become adept at catching fast-moving rodents, birds, and other prey successfully—well enough to feed themselves and survive independently. By fledging fairly early in spring, young owls have the rest of spring and all of summer, a period when prey are more plentiful, to practice their hunting skills.
One of the largest owls in the Chicago region, Great Horned Owls may stand two feet tall, and have wing spans of four to five feet. Females usually are larger than males, but otherwise the sexes look similar.