Great Horned Owl, Bubo virginianus
Note: this post, while published, is a work in progress, as are all posts in this series, My Photo Life List. My goal is to photograph every species of bird that is seen on a regular basis here in Michigan, working from a list compiled by the Michigan chapter of the Audubon Society. This will be a lifelong project, that I began in January of 2013, and as I shoot better photos of this, or any other species, I will update the post for that species with better photos when I can. While this series is not intended to be a field guide per se, my minimum standard for the photos in this series is that one has to be able to make a positive identification of the species in my photos. The information posted here is from either my observations or the Wikipedia, the online free encyclopedia, however, I have personally shot all the photos appearing in this series.
Great Horned Owl, Bubo virginianus
The Great Horned Owl is a large owl native to the Americas. It is an adaptable bird with a vast range and is the most widely distributed true owl in the Americas.
The Great Horned Owl is the heaviest extant owl in Central and South America and is the second heaviest owl in North America, after the closely related but very different looking Snowy Owl. It ranges in length from 43–64 cm (17–25 in) and has a wingspan of 91–153 cm (36–60 in). Females are invariably somewhat larger than males. An average adult is around 55 cm (22 in) long with a 124 cm (49 in) wingspan and weighing about 1.4 kg (3.1 lb)
There is considerable variation in plumage coloration but not in body shape. This is a heavily built, barrel-shaped species that has a large head and broad wings. Adults have large ear tufts and it is the only very large owl in its range to have them. The facial disc is reddish, brown or gray in color and there is a variable sized white patch on the throat. Its “horns” are neither ears nor horns, simply tufts of feathers.
The breeding habitat of the Great Horned Owl extends from subarctic North America throughout most of North and Central America and then down into South America south to Tierra del Fuego, the southern tip of the continent. It is absent from southern Guatemala, El Salvador and Nicaragua to Panama in Central, and Amazonia and the southwest in South America, as well as from the West Indies and most off-shore islands. They are the most widely distributed owl in the Americas.
It is among the world’s most adaptable owls in terms of habitat. The Great Horned Owl can take up residence in trees that includes deciduous, coniferous, and mixed forests, tropical rainforests, pampas, prairie, mountainous areas, deserts, subarctic tundra, rocky coasts, mangrove swamp forests, and some urban areas. It is less common in the more extreme areas (i.e., the heart of the deserts, extremely dense rainforests and in mountainous areas above the tree line), generally absent from non-tidal wetland habitat, and missing from the high Arctic tundra. It prefers areas where open habitats, which it often hunts in, and woods, where it tends to roost and nest. This species can occasionally be found in urban or suburban areas. However, it seems to prefer areas with less human activity and is most likely to be found in park-like settings in such developed areas, unlike Eastern and Western Screech Owls which are regular in suburban settings. All mated Great Horned Owls are permanent residents of their territories, but unmated and younger birds move freely in search of company and a territory, and leave regions with little food in winter.
Like most owls, the Great Horned Owl makes great use of secrecy and stealth. Due to its natural-colored plumage, it is well camouflaged both while active at night and while roosting during the day. Despite this, it can still sometimes be spotted on its daytime roosts, which are usually in large trees but may occasionally be on rocks. This regularly leads to their being mobbed by other birds, especially American Crows. Since owls are, next to Red-tailed Hawks, perhaps the main predator of crows and their young, crows sometimes congregate from considerable distances to mob owls and caw angrily at them for hours on end. When the owls try to fly off to avoid this harassment, they are often followed by the corvids.
Owls have spectacular binocular vision, allowing them to pinpoint prey and see in low light. The eyes of a Great Horned Owl are nearly as large as those of a human being and are immobile within their circular bone sockets. As a result, instead of turning its eyes, an owl must turn its whole head, the neck capable of rotating a full 270 degrees, in order to see in various directions without moving its entire body.
An owl’s hearing is as good as, if not better than, its vision. Owls have better depth perception and better perception of sound elevation (up-down direction) than human beings. This is due to the asymmetrical positions of owl ears on either side of the head. The right ear is typically set higher in the skull and at a slightly different angle. By tilting or turning its head until the sound is the same in both ears, an owl can pinpoint both the horizontal and vertical direction of the sound’s source.
Owls also have approximately 300 pounds per square inch (PSI) of crushing power in their talons, a PSI greater than the human hand is capable of exerting. In some cases the gripping power of the Great Horned Owl may be comparable to much larger raptor species such as the Golden Eagle.
Owls hunt mainly by watching from a snag, pole or other high perch, sometimes completely concealed by the dusky night and/or partially hidden by foliage. From such vantage points, owls dive down to the ground, often with wings folded, to ambush their prey. They also hunt by flying low over openings on the ground, scanning below for prey activity. On occasion owls may actually walk on the ground in pursuit of small prey or, rarely, inside a chicken coop to prey on the fowl within. They have even been known to wade into shallow water for aquatic prey, although this has been only rarely reported. Owls can snatch birds and some arboreal mammals directly from tree branches as well. The stiff feathering of their wings allows owls to produce minimal sound in flight while hunting.
Almost all prey is killed with the owl’s talons, often instantly, though some may be bitten about the face as well. Prey is swallowed whole when possible. However an owl will also fly with prey to a perch and tear off pieces with its bill. Very large prey, any that is notably heavier than the owl, must be eaten where it is killed for it is too heavy to fly with. In northern regions where such large prey is prevalent, an owl may let uneaten food freeze and then thaw it out later using its own body heat. When prey is swallowed whole, owls regurgitate pellets of bone and other non-digestible bits about 6 to 10 hours later, usually in the same location where the prey was consumed. Great Horned Owl pellets are dark gray or brown in color and very large, 7.6 to 10.2 cm (3.0 to 4.0 in) long and 3.8 cm (1.5 in) thick, and have been known to contain skulls up to 3 cm (1.2 in) wide inside them.
Prey can vary greatly based on opportunity. According to one author, “Almost any living creature that walks, crawls, flies, or swims, except the large mammals, is the great horned owl’s legitimate prey”. The predominant prey group are small to medium-sized mammals such as hares and rabbits, which are statistically the most regular prey, as well as any small to moderately sized rodent such as rats, squirrels, flying squirrels, mice, lemmings and voles. Other mammals eaten regularly can include shrews, bats, armadillos,muskrats, martens and weasels. Studies have unsurprisingly indicated that mammals that are primarily nocturnal in activity, such as rabbits, shrews or muroid rodents, are generally preferred.
The Great Horned is also a natural predator of prey two to three times heavier than itself such as porcupines, marmots and skunks. According to the Cornell Lab of Ornithology, the Great Horned Owl is the only regular avian predator of skunks. In one case, the remains of 57 striped skunks were found in a single owl nest.
Birds also compose a large portion of a Great Horned Owl’s diet, ranging in size from kinglets to Great Blue Herons and young swans. Regular avian prey includes woodpeckers, grouse, crows, pigeons, herons, gulls, quail, turkey and various passerines. Waterbirds, especially coots and ducks, are hunted fairly often; even raptors, up to the size of Red-tailed Hawks and Snowy Owls, are sometimes taken. Other birds, being primarily diurnal, are often snatched from their nocturnal perches as they sleep. The Great Horned Owl is a potential predator of any other owl species found in the Americas, of which there are several dozen. Bird prey are often plucked before eaten and the legs and much of the wings are torn off and discarded.
Reptiles to the size of young American alligators, amphibians, fish, crustaceans and even insects, centipedes, scorpions and earthworms are occasional supplemental prey. In addition, the Great Horned Owl will prey on domesticated animals, including cats and small or young dogs. Carrion is eaten with some regularity, including road-kills.
It is common for people to deal with troublesome wildlife by placing plastic replicas of Great Horned Owls on their property, since many small animals will actively avoid areas inhabited by them.
Great Horned Owls are some of the earliest-breeding birds in North America, seemingly in part because of the lengthy nightfall at this time of year. They breed in late January or early February and are often heard calling to each other regularly as early in the fall as October. They choose a mate by December and are often heard duetting before this time. For owls found in more tropical climates, the dates of the breeding season are somewhat undefined.
The male attracts the attention of his mate by hooting emphatically while leaning over (with the tail folded back) and puffing up his white throat to look like a ball. The female hoots back when the pair meet but is more subdued in both her hoot and display. Pairs typically breed together year after year and may mate for life, although they associate with each other more loosely when their young become mostly independent. Like all owls, Great Horned Owls do not build their own nest. They often take over a nest used by some other large bird, sometimes adding feathers to line the nest but usually not much more. Old crow and raven, Red-tailed Hawk or large squirrel nests are often favored in North America. However, they are far from dependent on the old nests of others and may use cavities in trees and snags, deserted buildings, and artificial platforms. Other nest sites have included a large gap in a tree trunk, sheltered depressions on rocks and even a heron’s nest in the midst of a heronry. Males select nesting sites and bring the females’ attention to them by flying to them and then stomping on them.
There are usually 2 eggs per clutch, but clutches range in size from 1 to 6 eggs (over 4 is very rare), depending on environmental conditions. The average egg width is 1.8 in (46.5 mm), the average length is 2.2 in (55.2 mm) and the average weight is 1.8 oz (51 g). The incubation period ranges from 28 to 37 days, averaging 33 days. The female alone does all the incubation and rarely moves from the nest, while the male owl captures food and brings it to her. Brooding is almost continuous until the offspring are about 2 weeks old, after which it decreases; during this time the male feeds both the female and the young. Young owls move onto nearby branches at 6 weeks and start to fly about a week later. However, the young are not usually competent fliers until they are about 10 to 12 weeks old. The offspring have been seen still begging for food in late October (5 months after leaving the nest) and most do not separate from their parents until right before they start to reproduce for the next clutch (usually December). Birds may not breed for another year or two, and are often vagrants (“floaters”) until they establish their own territories.
On to my photos, and I only have one in digital form, and it isn’t great, but it meets my minimum standard of being able to make a positive ID of the species:
This is number 84 in my photo life list, only 266 to go!
That’s it for this one, thanks for stopping by!