Great Horned Owl
Bubo virginianus
Great horned owls nest in urban areas, grasslands, shrublands, riparian woodlands, and coniferous forests from the plains to near treeline. They lay their eggs in used hawk or magpie nests, in hollow stumps, on building ledges, or even on the ground. They prey on almost anything that moves, including insects, songbirds, other owls, mice, rabbits, prairie dogs, squirrels, snakes, skunks, muskrats, and house cats.
These large, non-migratory owls vocalize year-round as pairs defend territories ranging from one square mile on the plains to two square miles or more in the mountains. Vocal activity usually peaks during the late fall to early winter courtship period. Nesting begins in January or February. After leaving the nest in May or early June, the fledglings spend several days walking around on tree limbs or on the ground. Young may remain with their parents until early winter.
Local populations have increased in recent decades as these opportunistic predators adapt to our urbanizing environment. Great horned owls have replaced long-eared owls in Boulder County riparian woodlands, and their predatory activities may have contributed to a decline in local burrowing owl populations. They also prey on barn owls.
Vocalizations: A low, “who-whoo, who whoo” (male), or a slightly higher “who-who-wh-whoo, wh-who-whoo” (female); assorted barks, screams, and squawks.
Nesting: February-May on plains, slightly later in foothills and mountains; 3-4 eggs in a hawk or magpie nest or a tree hollow; usually 1-3 fledged young.
Where to listen and look: Boulder Creek near Sawhill and Walden Ponds; Rock Creek Farm Open Space; White Rocks Trail.