GREAT HORNED OWLS
Bubo virginianus
by Shani Freidman
Sometimes called the "tiger of the air," the Great horned owl is one of our fiercest predators. Mostly hunting at night, sometimes during daylight, it ranges from the northern tree line of arctic Canada to the southern tip of South America. Its habitat is widely varied. You can find it hunting in woods, mountains, marshes, dunes, and open deserts. In Arizona it is fairly common, except in the high central southern mountains. Inconspicuous during the day, it quietly roosts in deep vegetation, taking off silently if disturbed.
One of the largest and most powerful of all North American owls, the Great horned is from eighteen to twenty five inches long, with an impressive wingspan of three to five feet. Males and females are similar in appearance, but the female is the larger of the two. In general, the body is brown, spotted with darker brown. Their ears are tufted, and their so-called horns are simply tufts of feathers. White throat feathers contrast with dark cross-barred under parts. Feathers cover their legs up to the talons. The plumage is variable among the many subspecies, from a very pale arctic subspecies to the chocolate brown found in Central America. In Arizona, three pale hued subspecies have been identified, mostly varying in the color of their feet.
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Photo by Richard of Searchnet Media
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Another way to identify Great horned owls is by learning their distinctive sounds. Some people think their call sounds like, "Don't kill owls, save owls"- a five syllable sentence (three short syllables, followed by two long ones) hooted on a single pitch with an almost dovelike quality. However, variations are common, from a three syllable, "Don't kill owls" to longer series with additional single or double note trailing phrases. Like most owlets, the young give out a rasping hiss when hungry. When attacking an enemy, angry growling krrooo-ooo notes are heard, along with downright screams. If defensive or aggressive, a Great horned makes itself look larger by spreading its wings to the side, tilting its body forward, and fluffing up its body feathers-while hissing or snapping its bills together to produce a clicking that can be heard fifty yards away. The young also scream as a food call or to attract the attention of an adult. If defending her nest, a female makes short, laughing wha-whaart notes or a similar chuckling whar, whah, wha-a-a-ah sound. Mated pairs of owls call to each other, probably to coordinate and strengthen their pair bond.
The binocular vision of the Great horned owl is spectacular, allowing them to see in very low light and pinpoint prey. Their eyes are nearly as big as ours and fixed in circular bone sockets. They cannot turn their eyes, so they pivot their heads instead. Their neck can swivel up to 270 degrees, allowing them to see in many directionswithout turning their body.
Their hearing is just as amazing. Their ears are not in the same position on each side of their head. The right ear is set higher up and at a slightly different angle. By tilting and/or turning its head, the owl can pinpoint both the vertical and horizontal direction of a sound. Their depth perception and ability to discern sound elevation (up/down direction) is far superior to ours. They can even hear small rodents in their burrows under the ground.
After nightfall, using acute sight and hearing, a Great horned owl perches high above and silently swoops down to catch prey in its powerful feet and talons. The bird has a crushing power of 200 to 300 pounds per square inch in its talons. Compare this to the 60 pounds per square inch in the hand of an adult man. It is an opportunist, dining on what it can find, from the smallest shrews to large hares and rabbits. It is so fond of squirrels that it strikes leaf nests in the daytime to flush them out. Chipmunks, wood rats, Norway rats, mice, muskrats, minks, weasels, skunks, ground squirrels, pocket gophers, woodchucks, opossums, and even porcupines are taken. Cottontail rabbits are a significant food source. Domestic cats, small dogs, snakes and bats are also eaten. Its appetite for domestic fowl has often placed the Great horned owl at the wrong end of a shotgun. It consumes grebes, ducks, geese, swans, bitterns, small herons, coots, gallinules, rails, phalaropes, pheasants, quail, grouse, domestic turkeys, chickens and guinea fowl. Mourning doves, hawks, other owls, flickers, woodpeckers, jays, crows, blackbirds, meadowlarks, buntings, juncos, sparrows, mockingbirds, and robins are on the menu. It even goes into chimneys after swifts. Occasionally, it eats frogs, eels, goldfish, bullheads, perch, small alligators, crayfishes, crickets, beetles, grasshoppers, katydids, and scorpions. It goes after whatever it can catch and carry off to its feeding roost (usually an abandoned nest, hollow stump, or fallen log near its nest) where it rips apart and devours its meal. Owl pellets (regurgitated, elliptical balls of undigested fur, bones, hair and feathers) collect near the feeding roost.
Great horned owls begin courtship behavior as early as October. The male hoots as he gradually approaches the female, landing on perches closer and closer to her. When they can both see each other, they bow and hoot, simultaneously dropping their wings and cocking their tails upward at nearly a 90 degree angle. While hooting their duet, the female's sound is higher pitched and at a quicker tempo than the male's. The white feathers below the chin are conspicuously fluffed up in time with the calls, an effective visual signal in dimly lit places. The male walks and hops on the ground, or throws his head back and bill snaps. While engaged in prolonged mutual calling, the birds rub their beaks together. Bill snapping can occur if the female gets aggressive. In this case, the male renews his posturing and gradual approach. If the female accepts him, they engage in allopreening, i.e. alternately pecking at the feathers around the other's bill and head. Allopreening seems to reduce tensions between the pair. They may fly together for a short distance. Every now and then, the male brings a meal to his mate. Once paired, the owls stay close together, often roosting together in the daytime. They remain mated until the death of one of the pair.
Great horned owl does not build its own nest. It lays claim to an existing nest made by a Red-tailed hawk, Bald eagle, heron, or crow. Usually, it finds an unused nest early in the year well before other birds are ready to nest. If the bird that built the nest finds an owl in residence, it does not contest the ownership of the nest, and builds a new one of its own. Great horned owl also uses rocky cliffs, caves, hollows of trees, or even the ground for a nesting site. It has accepted large manmade platforms built in trees. Jon designed large houses for them that were immediately accepted and used on a private property in northwest Tucson.
They are among the earliest birds to breed in North America, beginning to breed in the dead of winter (late January or early February) in northern climes. In Arizona, it nests in the spring, with eggs hatching in June. Incubation duties are shared by both parents, taking from 26 to 36 days. The adults feed the young on the ground before they can fly, 63 to 70 days after hatching. Some parents are fiercely protective of their young, attacking intruders. They have been known to assault furry caps, apparently mistaking them for prey.
Our new world Great horned owl is very closely related to the Eurasian Eagle owl. Together, they are a superspecies, i.e. two species that are clearly derived from a common ancestor, but are too distinct to be considered a single species. The two birds have been bred in captivity.
Even though it is constantly harassed by man, the Great horned owl continues to survive throughout most of our continent. Surely its highly secretive nature and extreme adaptability helps its survival. Habitat disruption, road kills and indiscriminate shooting are the major causes of its population decline in North America.