The great horned owl (Bubo virginianus) is one of the most common and widespread owl species in North America. These large, powerful owls can be found in a variety of habitats across the continent, from dense forests to open deserts. Great horned owls are opportunistic nesters, using cavities in trees, rock ledges, abandoned buildings, and even old nests built by other birds. But where exactly do these owls prefer to build their nests? In this article, we’ll take a deep dive into the nesting habits of great horned owls to find out where they typically choose to raise their young.
Nesting Requirements
Great horned owls have fairly broad requirements when it comes to selecting a nesting site. The main things they look for are:
- A cavity with enough space for the female to incubate eggs and brood young owls. Great horned owl nests are typically 2-3 feet wide and 8 inches to 2 feet deep.
- A sturdy structure that can support the weight of adult owls and growing young. Great horned owls can weigh up to 3-4 pounds.
- Some degree of privacy and concealment from predators and the elements.
- Easy access in and out of the nest cavity.
- A location high enough off the ground to keep eggs and chicks safe from ground predators.
Beyond meeting these basic criteria, great horned owls are quite flexible in selecting nest sites. They are unafraid of nesting close to human habitation and will readily occupy nest boxes and artificial platforms intended for hawks, crows, or other large birds.
Favorite Nest Sites
Although great horned owls utilize a diversity of nesting spots across their range, there are a few key types of sites they tend to favor:
Cavities and Crevices in Large Trees
The most classic great horned owl nest is inside a natural cavity or crevice in a large, mature tree. Owls look for openings created by damage, decay, or breakage in the tree trunk or major branches. Hardwood trees like oak, elm, cottonwood, willow, and maple are often chosen. Conifers like pine, spruce, and juniper may also be used. Cavities and platforms in the main fork of broad-leaved trees are another favorite.
Cliff Ledges and Crevices
In areas with rock cliffs, bluffs, or canyon walls, great horned owls will readily adopt sheltered ledges and openings as nest sites. These may be bare rock ledges or small caves. Nesting may also occur in crevices and cavities on the underside of fallen boulders or rocky overhangs.
Old Nests of Other Large Birds
Great horned owls are notorious for taking over the abandoned nests of hawks, crows, herons, and other large birds rather than building their own nest from scratch. Platform nests built by red-tailed hawks are a common choice. Owls may do some tidying and rearranging of the existing nest but often move right in.
Nooks and Crannies on Manmade Structures
From barns and silos to stadium light fixtures, great horned owls will occupy a wide array of manmade structures. They most often use cavities and sheltered spots on buildings, bridges, and similar structures that mimic natural nest sites. But these adaptable owls aren’t overly picky – if the spot is safe and roomy, they may settle in for nesting.
Regional Differences
Great horned owls occupy an incredibly diverse range of habitats across North and South America. Unsurprisingly, the specific types of sites used for nesting can vary quite a bit across this vast range:
Eastern Forests
In eastern forest environments, great horned owls primarily nest in natural tree cavities or utilize old hawk, heron, or crow nests built in tree forks. Main cavity sites include oak, beech, sycamore, elm, and maple. Old crow nests in pines, hemlocks, and other conifers are also used.
Western Mountains and Deserts
In the western mountains and arid desert environments, great horned owls are somewhat more reliant on rock outcrops, bluffs, and canyon walls. This is due to fewer large, old trees. But they will use trees like cottonwoods along waterways where available. Nesting also occurs in mine shafts, caves, and rocky overhangs.
Northern Forests
Cavities in poplar, birch, spruce, and other northern tree species are the major nest sites across Canada and Alaska. Nests are also common on cliffs and bluffs, or in sheltered rock overhangs. Great horned owls here may take over old nests used by large hawks or ravens.
Tropical Environments
From the Florida swamps to the Amazon rainforest, great horned owls utilize cavities in palms, mangroves, and mighty ceiba trees within tropical regions. They also occupy nooks and ledges on cliffs, ruins, and temples within ancient Mayan cities in Central America.
Nest Height
When nesting in trees, great horned owls typically choose cavity sites high up on the main trunk or in major limb forks. Average nest height is usually 20-60 feet above the ground but can occasionally be as high as 100 feet. This provides protection from terrestrial predators and a commanding view of the surrounding territory.
On cliffs and canyon walls, nests may be situated anywhere from just a few feet to over 100 feet off the canyon floor or above ground level. The availability of suitable ledges and outcrops dictates height in rock crevice situations. In manmade structures, owls usually nest at heights over 15-20 feet.
Typical Nest Heights by Location
Nest Location | Typical Height Range |
---|---|
Tree cavities | 20 – 60 ft |
Cliffs and canyons | 5 – 100+ ft |
Manmade structures | 15 – 60+ ft |
Nest Construction
Unlike many birds, great horned owls do not build an elaborate nest structure from scratch. The female will, however, arrange materials already present in or around the nest site into a scrape or cup to hold the eggs. Typical nest materials include:
- Sticks, twigs, and debris already in tree cavity
- Leaf litter or pine needles on rocky ledges
- Grasses and weeds stuffed onto sheltered manmade perches
- Lining feathers plucked from her own breast
Females may do some minor pruning of sticks around the cavity entrance or shuffle materials into a more cohesive platform. But great horned owl nests are generally messy, sparse affairs in comparison to hawk or crow nests – just enough to provide a foundation for the eggs. The eggs and chicks are insulated by the female’s own body heat as she broods them.
Reuse of Nests
It is common for the same great horned owl pair to use the same nest over multiple years, though they may also shift occasionally to alternate sites within their territory. Advantages of reusing a nest include:
- Saved effort – minimal repair needed to get nest ready
- Proven safe location
- Familiar territory
In one study, 13 out of 20 great horned owl nests monitored were reused for between 2-7 years before the pair shifted to a new site. However, nest reuse may become less likely if site conditions change, such as loss of a tree cavity or increased human disturbance near the nest. Pairs are capable of building new nests from scratch but seem to prefer established sites when available.
Timing of Nesting
Great horned owls begin nesting much earlier in the year than most other owl species. This head start allows young owls enough time to fledge and leave the nest before summer, when food is most abundant. Here is the general nesting timeline:
- October – January: Breeding and nest site selection
- February – March: Egg laying and incubation (lasting ~30 days)
- April – May: Hatching and rearing young (fledging in 6-7 weeks)
- June – July: Young owls leave nest and disperse
Further north, great horned owls may not start nesting until late winter, with young fleeing in mid-summer. In the southernmost parts of their range breeding can start as early as September. Pairs mate for life and often return to the same territory each year.
Habitat Near Nest Sites
Given their diverse habitat range, great horned owl nests may be situated near a variety of landscape features:
- Forest edges – provide hunting perches and access to open areas
- Fields and meadows – source of rodent prey like voles and mice
- Rivers, lakes, swamps – hunting habitat with amphibians and fish
- Suburban neighborhoods – abundant prey like rabbits, skunks, rats
Nest locations are strongly influenced by availability of suitable cavities and security from predators first and foremost. But proximity to high quality hunting habitat and reliable prey sources may also play a role in nest site selection.
Protection Status
Great horned owls are widespread and adapt readily to human settlement and habitation changes. They are not considered threatened or endangered in most regions. However, it is illegal to disturb or interfere with active nests in many areas. Some key protections include:
- Covered under the Migratory Bird Treaty Act in the U.S. and Canada – illegal to harm nests
- State and local regulations may protect occupied nests
- Species of Special Concern in a few states like Minnesota and New Mexico
Responsible birders and photographers keep their distance from nests to avoid stressing owls during the critical breeding season. Landowners and developers should also avoid logging or removing trees, buildings, or cliffs used for nesting. Following regulations and best practices allows both owls and humans to coexist safely.
Conclusion
Great horned owls demonstrate a high degree of adaptability and variation when it comes to selecting nesting sites across the Americas. Tree cavities, cliff ledges, and old hawk or crow nests in the main fork of trees represent classic nest locations. But these opportunistic owls will occupy a diversity of natural and manmade sites that offer sufficient space, protection, and security. While specific nest spots may shift over the years, pairs often reuse favorable nests for many seasons. Understanding the nesting requirements and habits of great horned owls can help sustain healthy populations of these iconic raptors across their range.