The California great horned owl, known by its scientific name Bubo virginianus pacificus, is the type of great horned owl most likely to be seen in Southern California and San Bernardino County in particular. The great horned owl, of which there are more than 20 subspecies, was once referred to by naturalists as the “winged tiger” or “tiger of the air,” as well as the hoot owl. The Californian great horned owl is an extremely adaptable bird which ranges throughout Central and Southern California west of the Sierra Nevada except the San Joaquin Valley, south to Northwestern Baja California. It intergrades with pallescens in San Diego County.
Resident all-year, the California great Horned Owl sports a very rich brown, dark underside with barring. The humeral area is black. Feet are mottled dark. The facial disc is often darkly mottled. Among owls, this is a fairly small-bodied race, in fact including the lightest wild great horned adult owl ever weighed. The wing chord length in males averages 13.09 inches and in females averages 13.83 inches. Body mass in males ranges from 1.499 to 2.804 pounds, averaging 2.186 pounds. In females, the weight ranges from 1.819 to 3.677 pounds, averaging 2.894 pounds. Tail length is 6.9 to 8.6 inches 8.0 to 9.1 inches in males and females, respectively. Bill length is 1.3 to 1.6 inches.
In most aspects of their behavior, great horned owls are typical of owls and most birds of prey. There is disagreement among ornithologists about whether the great horned owl is a bird of “essentially low intelligence,” as has been concluded by Paul L. Errington, or whether they are intelligent birds, as enunciated by William J. Baerg. The assessment of the horned owl’s intelligence for some turns on the willingness of those birds taken captive by humans to accede to training. Most captive horned owls, once mature, appear to resent captivity and may attack their keepers. This makes them ill-suited for falconry or entertainment purposes, thus resulting in some considering the birds to be stupid. This may say more about the narrow point of reference these humans have than about the birds themselves, which have a natural affinity for freedom.
Its primary diet appears to be rabbits and hares, rats and mice and voles, although it is an opportunistic feeder and freely hunts any animal it can overtake, primarily rodents and other small mammals, but also larger mid-sized mammals, various birds, reptiles, amphibians and invertebrates. According to Carol Lee, “Almost any living creature that walks, crawls, flies, or swims, except the large mammals, is the great horned owl’s legitimate prey.” In fact, the great horned owl has the most diverse prey profile of any raptor in the Americas.
The horned owl makes great use of secrecy and stealth. Its natural-colored plumage camouflages it well while active at night and while roosting during the day. In daytime it roosts usually in large trees and occasionally in crevices or small caves in rocks or in dense shrubbery. Generally great horned owls are active at night, although in some areas may be active in the late afternoon or early morning.
Hunting activity tends to peak between 8:30 pm and 12:00 am at night and then can pick back up from 4:30 am to sunrise. Owls hunt mainly by watching from a snag, pole or other high perch. During hunting forays, they often fly about 160 to 330 feet from perch to perch, stopping to survey for food at each, until they sense prey below. From such vantage points, owls dive down to the ground, often with wings folded, to ambush their prey. Effective maximum hunting distance of an owl from an elevated perch is 300 feet. Due to their short but broad wings, great horned owls are ideally suited for low speed and maneuverability, though they can reach speeds of more than 40 miles per hours in level flight. Despite reports that they do not hunt on the wing, they also sometimes hunt by flying low over openings on the ground, scanning below for prey activity. Owls can snatch birds and some arboreal mammals directly from tree branches in a glide as well. The stiff feathering of their wings allows owls to produce minimal sound in flight while hunting.
Almost all prey are killed by crushing with the owl’s feet or by incidentally stabbing of the talons, often instantly, though some may be bitten about the face as well. Prey is swallowed whole when possible. Not all prey can be swallowed at once, and owls will also fly with prey to a perch and tear off pieces with their bill.
Many large prey items are dismembered. A signature method when dealing with large prey for the great horned owl is to behead the victims before it takes to its nest or eating perch. The great horned owl will also crush the bones of its prey to make it more compact for carrying. Many owls will accrue a cache of prey, especially those who are nesting. Caches are kept in a safe location, usually the crotch of a tall tree.
The great horned owl is one of the earliest nesting birds in North America, often laying eggs weeks or even months before other raptorial birds. The courtship for the great horned owl runs from October to December and mates are chosen by December to January. This species is strictly monogamous. The male attracts the attention of his mate by hooting emphatically while leaning over and puffing up his white throat. The white throat may serve as a visual stimuli in the low light conditions typical of when this owl courts. He often flies up and down on a perch, while approaching the potential mate. Eventually, he comes to approach the female and tries to rub his bill against hers while repeatedly bowing. If receptive, the female hoots back when the pair meet but is more subdued in both her hoot and display. The male may convince the female by bringing her freshly caught prey, which they will then share. While males often hoot emphatically for about a month or six weeks towards the end of the year, the period where females also hoot is usually only a week to ten days. 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. Pairs rekindling their reproductive relationship in the winter may perform a milder courtship to strengthen pair bonds before producing young.
Males select nesting sites and bring the females’ attention to them by flying to them and then stomping on them. Like all owls, great horned owls do not build their own nest. They nest in a wider variety of nest sites than any other North American bird. Most tree nests used by great horned owls are those constructed by other animals, often from a height of about 15 to 72 feet off the ground. They often take over a nest used by some other large bird, and add no more to the nest than feathers.
Egg laying by the California great horned owl takes place from early February to late March. There are usually two eggs per clutch, but clutches range in size from one to six eggs. The average egg width is 1.83 inches, the average length is 2.2 inches and the average weight is 1.8 ounces. The incubation period ranges from 28 to 37 days, averaging 33 days. The female alone usually does all the incubation and rarely moves from the nest, while the male owl captures food and brings it to her, with the first nightly food delivery typically occurring soon after dark. The young weigh around 1.22 oz at birth on average and can gain an average of about 1.17 ounces a day for the first four weeks of life, with typical weights in the range of 1.8 or 2.2 lb pounds by 25–29 days for males and females, respectively. The nestling owls develop mostly in behavior between two weeks and two months of age, in which time they adapt the ability to defend themselves, grasp foods and climb. Vocally, the young are able to exert weak chirps while still in the egg, developing into a raspy chirp shortly after hatching. 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 age at which the young leave the nest is varied based on the abundance of food.
Mated pairs of horned owls occupy territories year-round and long-term. Territories are established and maintained through hooting, with highest activity before egg-laying and second peak in autumn when juveniles disperse.
