Great Horned Owl

(Bubo virginianus)





Family:
Strigidae (STRIJ-ih-dee). The Typical Owl Family, includes about 140 owls except for barn owls and bay owls.

Genus: Bubo (BEW-boh) is from the Latin word meaning "owl" or from the Greek word for "eagle owl" used by the great 1st century Roman naturalist Pliny (Gaius Plinius Secundus). Great horned owls are related to the eagle owl of Eurasia.

Species: virginianus, meaning "of Virginia" where the first specimen of great horned owls was collected. The common name "horned owl" comes from the large ear tufts.

Geographic Range

Great horned owls occur all over the United States and most of Canada, and southward to Central and South America to the Straits of Magellan. They are one of the most widespread species of owls. They mostly reside year round in their territories, but ones from the far north move southward in fall or winter.

Description

Great horned owls are big and bulky (3-4 pounds), standing 18-25" tall with a wingspan of 36-60" long. Males and females are similar in appearance, except the female is the larger of the two. The plumage of the great horned owl varies regionally, from pale to dark. In general, they have brown body plumage covered with darker brown spots and white throat feathers that contrast with the dark cross-barred underparts. The white feathers stand out like a collar against the darker underside feathers. Some great horned owls may be very pale underneath, but still the white collar stands out.

The great horned owls facial disk may have orangish or grayish feathers, and whiter feathers that form a V between the yellow eyes with black pupils. Their ear tufts are large and set far apart on the head. Just like a dog, great horned owls use these ear tufts to convey body language - when they are irritated the tufts lie flat and when they are inquisitive the ears stand upright.

In summary, four good field marks for the great horned owl are: size, eye color, ear tufts and the white collar.

Voice

Of course, if you hear a great horned owl call, that is a great identification aid. Their call is a series of deep hoots, from 3 to 8 notes long, and sounds like - "Whose Awake, Me Too", with the "Me Too" part descending in tone or who-who-ah-whoo, who-ah-whoo. Like a coyote howl, the call of the great horned owl is a classic sound of the wild and can be heard a long way off. And when nesting pairs of great horned owls call, the female has the higher pitched voice.

Young great horned owls have a screeching hunger call that is also very loud and sounds like short blasts of escaping steam through metal pipes.

Habitat

Found in woods, mountain forests, desert canyons, marshes, city parks, and urban forests. The owls prefer open areas to dense woodlands or nest sites close to the edge of a forest where they can hunt.

Breeding and Nesting

Great horned owls are one of the earliest spring nesting birds; eggs may be laid in January or February through April. They use abandoned stick nests of a hawk or heron or crow, but also nest in rock alcoves, hollows of trees, abandoned buildings, or sometimes on the ground.

Throughout the winter, courting great horned owls will light up their nesting territory with nighttime hooting. Generally 2-3 white eggs are laid, although they may lay up to 6 eggs. Both the male and female incubate the eggs for 30-35 days. The young are fed by both parents, and the parents fiercely defend their nest site against intruders. If young owls fall out of the nest prematurely, the adults will feed the bird on the ground.

The young fledge from the nest at 45-55 days old.

Great horned owls can live greater than 12 years; some captive birds have lived to 29 years old.

Food and Hunting

Great horned owls tend to perch during the daylight hours in a protected rocky alcove or on a tree limb. They mainly hunt at night, but may hunt in daylight hours. From a quiet perch, the owl listens for sounds that betray a creature's presence. They may move about from tree to tree to get a better fix on the source of the sound. Once they pinpoint the sound, the owl silently swoops in, spreads its talons wide and pounces on its prey - known as the "perch and pounce" hunting method. Smaller prey is swallowed whole, but larger prey are torn into pieces.

Great horned owls eat a wide variety of prey, both small and large. Cottontail rabbits seem to be a prominent food, but the owls will take squirrels, shrews, jackrabbits, muskrats, mice, weasels, skunks, pocket gophers, snakes, domestic cats, bats, beetles, scorpions, frogs, grasshoppers, and a wide variety of birds, from small passerines like juncos and sparrows to wild ducks, grouse, pheasants, and even other owls. It seems that the world is one big smorgasbord to a great horned owl.

Several hours after an owl has eaten, its stomach forms a pellet of fur, feathers, exoskeletons, and bones - indigestible parts of its meal. The owl then "upchucks" this pellet. Owls may have a favorite roost or perch spot where they cast out these pellets. Scientists collect the pellets and gently pull them apart in their laboratories to see what the owl has been eating.

Behavior

Great horned owls roost during the day in protected rocky caves or on tree limbs. Sometimes if you see an owl during the day, stop and watch. If the owl is not bothered, it will slowly closes its eyes and fall asleep. Its talons clutch the tree branch and keep the owl from falling off its perch!

Contrary to popular belief, owls can not turn their heads completely around. They can rotate their heads 270 degrees, thanks to extra vertebra in their necks. Because their eyes are fixed in their sockets - they can't move their eyes up or down or side to side - the owl has to move its whole head to compensate for the fixed eyes.

When owls are awake, they use their hearing and eyesight to alert them of danger or possible prey. Great horned owl eyes, which are almost as large as a humans, allows a great amount of light to pass through the pupil, so the owl can see in dark conditions. If a great horned owl was as big as a human, its eyes would be the size of oranges!

Owls have incredible senses of hearing, a trait that allows them to hunt at night. Their ears are located on the sides of the head, but are off-set, not symmetrical like human ears. The openings of the ears are slightly tilted in different directions - often the right ear is longer and set higher up on the skull. Plus, owls have soft feathers that surround the openings which they can spread to make a funnel for sound to enter the ear. This enables the owl to use triangulation to pinpoint the source of a sound, when the prey can not be seen. By tilting or moving their head until the sound is of equal volume in each ear, the owl can pinpoint the direction and distance of the sound.

Owl feathers are soft, almost like polar fleece to the touch. This helps to deaden the sound of air rushing over the feathers while the bird is in flight. Also the front edge of the first primary or wing feather is toothed like a hand saw. This helps wind pass over the wings and keep the bird's flight noiseless. It wouldn't be easy to catch prey at night if you were crashing around in the dark!

Additional Notes

Some biological supply houses sell sterilized owl pellets for classroom use. These are a great way for students to investigate what types of foods owls eat.

Owls have a third, opaque eye membrane, called the nictitating membrane. This membrane helps to clean the eye of material and protect the eye from the brightness of day or foreign objects at night.

Owls have four toes on each foot, like most birds. Instead of having three toes in front and one in back, an owls outer toe is reversible - it can rotate so that there are two toes in front and two in back. This helps the owl grip a perch but also creates a bigger "mitt" when it swoops down to catch prey - kind of like the difference between a catcher's mitt and a shortstops. At night an owl needs all the advantages they can muster to capture prey.

The owls facial disk is shaped like a shallow bowl. This shape acts like a parabolic dish, to help funnel sound into the ear openings.







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