Throughout history people have attributed various human characteristics to owls. The Greeks depicted their goddess of wisdom as an owl. Even today, pictures of the Great Horned Owl, Bubo virginianus, are used to symbolize the "wise old owl." Early Romans and some Native American Indians believed that owls were messengers of death. Europeans and American settlers associated the owl with witches and the devil.

DESCRIPTION

The great horned owl is 18-25 inches long and has a wingspread of 48-60 inches. The great horned owl weighs 3-5 pounds. It is the same size as the snowy owl which occasionally wanders down from the arctic. The gray owl of Canada is larger but weighs less.

The plumage (feathers) of the great horned owl is very mottled. Its back is dark brown with black bars which look like broken or uneven stripes. The throat is white. Its ear tufts are edged in black. The owl appears to have eyebrows (actually feathers). Its facial disk (face--made up of feathers) is reddish in color and is surrounded by a wide white collar. The owl's breast is white or buff with dark brown or black barring. Both sexes share the same coloration. Females are about 1/3 larger than males. Its large head, flat face, short neck and white throat make it easy to identify when seen in flight. Its large yellow eyes are also distinctive.

POPULATION/DISTRIBUTION

Great horned owls are familiar to most Americans. They live in most of North America and range from the Arctic to South America. Owl populations vary widely even in excellent habitat, but the reasons for this are not well-known. It is believed that prey abundance plays a role.

HABITAT

Great horned owls maintain permanent home ranges. The home range must provide food and water on a year-round basis. The size of a specific owl's home range will vary widely depending on the topography (layout of the land), type of plant life and various other environmental conditions. The home range can vary from hundreds of acres to several miles in size.

The great horned owl's home range normally includes a large woodland, adjacent fields and smaller woodlots. Choice habitat includes nesting sites, daytime roosting sights, and good hunting territory.

Owls use nests of other large birds such as crows and hawks, and large tree hollows. Others use cliff ledges, or caves as nesting sites. During daylight hours, the great horned owl needs a roost which is not easily visible. They prefer roost trees located some distance away from other trees in the area. Open fields and forest edges serve as hunting territory.

Red-tailed hawks and great horned owls frequently share the same home range since the hawk hunts by day and the owl by night. Sometimes owls primarily use hawk nests for their own nest.

FOOD AND FEEDING BEHAVIOR

Adaptations for capturing and eating prey. Owls are one of the few predators which can use either sight or hearing to precisely prey. Their eyes are large and during darkness, the pupil of the eye expands to fill the entire eye. The owl's pupil has many light detecting nerve cells (rods). The back of the eye (retina) has many rod-shaped receptor cells for gathering light.

Their eyes are located on the front of a fairly flat face which gives them excellent binocular vision. Binocular and 3-dimensional vision allows the owl to determine the distance to its prey. Binocular vision is needed by owls and other birds that hunt living prey.

The owl is only able to see what is directly in front of it. It rotates its head to see possible prey. Contrary to popular belief, the owl cannot rotate its head all the way around, but can turn it over halfway around to look backwards. Owls have poor close range vision and may back away to see clearly.

Owl ears are large holes which are covered by special feathers and are located just behind the facial disk feathers on both sides of the head. The shape of the owl's head and ears and the arrangement of feathers allow the owl to hear very faint sounds. Owls are able to hear sounds such as mice chewing or squeaking up to 900 feet away. Scientists have demonstrated that owls can locate prey just by sound.

The flight of the adult great horned owl is powerful, swift, unfaltering, and silent. It stays close to the ground while flying to catch the desired prey. The owl's wing is adapted for silent flight. The wings are large compared to a small body. This allows for less wing flapping. Owls also use gliding which is quieter than flying. The edges of the owl's wing feathers are a soft fringe which helps to dampen the sound of air rushing through the feathers.

The talons of the great horned owl are zygodactylous (2 talons face forward, 2 face backwards). This permits the owl's feet to operate like a vise or tongs when catching prey. The talons pierce its prey and lock into place when the owl's feet strike its prey. They remain in place until the owl straightens its leg which releases the tendon holding the talons in this position. The talons give the great horned owl one of its nicknames--the meathook!

Feeding Techniques. Great horned owls hunt at twilight and at night. They hunt during daylight hours only when food is extremely scarce or during heavily overcast days. Their main hunting technique is to perch in a tree at the edge of a clearing or roadside and wait for prey to move underneath. Then, with a swift and shallow dive, they catch prey in their talons.

Owls usually eat small animals by beginning at the head and eating backward. They may pluck birds before consuming them. Owls swallow small prey, such as rats or mice, whole and head first. Owls consume the bones, fur and feathers as well as the edible meat. The hair, fur and bones are later regurgitated (spit out) as pellets which are also called castings (clumps of indigestible parts of prey). Piles of castings at the foot of trees identify owl roosting trees. They are also found at the base of other perches or in open fields.

Owls prey on a wide variety of birds and small mammals. Common prey include various mice, or rodents such as muskrats, squirrels or woodchucks. Owls also eat cats and rabbits. They may eat geese, ducks, chickens, crows, various song birds, or even hawks, bats and other owls. Some owls eat snakes, fish and crayfish. The great horned owl is well known for eating skunk--despite its strong odor. Owls may feed on carrion (dead animals). This opportunistic feeding behavior allows owls to remain on the territories year-round.

When a preferred prey species is extremely abundant, some owls eat only a specific portion of the body, such as the head. This contributes to the great horned owl's reputation as being a bloodthirsty predator.

BEHAVIOR

Courtship and Reproduction. Male owls beginning hooting to locate a female as early as October, November and December. Their hoot travels across long distances and they show excitement when hearing a return hoot. Courtship includes plenty of loud hooting. Once the pair meets, they face each other, snap their bills and rub their bills together.

During the courtship display the male bows his head, ruffles his feathers, droops his wings, and thrusts his tail skyward. He swells his white chest and gives a long, drawn out hoots.

The female inspects various nesting sites as part of courtship. They are not particular about nesting sites and may use old nests of hawks, crows, or squirrels. Owls also use hollows, broken-off snags and decayed tops of old or dead trees. Owls occasionally take over eagle nests-forcing the eagles to rebuild before laying their eggs. Nest sites may be used for several consecutive years if prey is abundant.

The male owl frequently presents food to his mate while courting. Scientists believe that courtship feeding helps to supply the female with adequate nutrition in order to form and lay a clutch of eggs within a short period. It may also serve to prevent the female from killing and eating her suitor.

After the courtship displays end, the male continues to hoot to maintain territory and the female remains near the selected nest until time to lay the eggs. She lays them in the debris (wood chips or other plant matter) in the bottom of the nest. In Michigan, egg laying begins in mid to late February. The number of eggs laid seems to be linked to available food supplies. Normally the female lays 2-3 dull white, thick-shelled, oval-shaped eggs. Owls lay only one clutch of eggs per season. Some females nest only every other year. Females in prime habitat may nest every year.

Incubation of the eggs lasts through the winter. Both the females and the eggs can survive extremely cold weather. Incubation usually takes 26-35 days with both sexes sharing in the process. The male feeds the female during this time.

Once the owlets hatch, the male brings large quantities of food to the nest. Prey is stored in the nest, since young owlets eat their nest mates if not kept constantly fed.

Newly hatched owls are covered with white natal (birth) down. Their eyes open at 9 days and function poorly for the first 2 weeks after opening. The owlet cannot hold up its head. After 3 weeks buff-colored, mottled looking down replaces the natal down. The owlets needs constant brooding (female sits on nest and covers owlets) to protect them from cold and predators. A female owl will viciously attack both animal and human invaders during this time.

Owlets begin growing their primary feathers (main, adult feathers) at 3 weeks of age. They have light yellow eyes with blue pupils. Less brooding is necessary and they are very active about the nest. Owlets learn to eject excrement (body waste) over the side of the nest but sometimes fall due to their clumsiness. About this time the owlets begin using a defensive display when disturbed. They raise their feathers, fan their wings downward, and hiss or snap their bill.

After 5-6 weeks, the female coaxes the owlets out of the nest by offering food from a nearby branch. The owlets first flight out of the nest, at 9-10 weeks, is to the ground. They quickly scramble up a tree to get away from ground level predators. If approached by a predator, they assume a hiding pose by sitting still and erect against the side of the tree. If this pose fails, they fly to ground and present the defensive display.

Feedings become irregular but the young owlets remain with the female and beg for food until September or October. During mid-June, the young owlets use their inborn instinct to attack prey. Young owls leave their parent's home range in autumn, when they are fully independent and can find their own hunting territory.

Territories. The territory for a mated pairs may range 1/3 of a mile to 2-5 square miles. Some ornithologists (scientists who study birds) believe that owls form permanent pair-bonds. If one member of the pair dies, the survivor remains in the home territory until another mate arrives.

Owls defend their territories from other owls. Defense occurs during breeding times. It lasts from 1 month before breeding until the young owlets leave the parental territory. Adults may wander across territory lines for a short time before the next breeding season begins. They frequently allow other types of birds such as hawks to live in their territory.

Owls with large territories frequently spend each season in a different part of their territory. Owls use specific areas of their territory for nesting and roosting. Some birds use certain trees so regularly that observers can predict in which trees they will find the owl in during a specific season.

During the winter and fall, owls prefer evergreen roost trees since they provide daytime cover. When these are not available, owls will adapt to any place that provides as much concealment as possible during daylight hours. They seem to prefer to roost in isolated trees in small forest openings.

Some northern great horned owls migrate to an area south of their normal ranges when winter food supplies are scarce. Whenever possible, they remain on their home ranges the year-round.

Voice/Sound. Great horned owls make a hoot that sounds like: who ho-hooo, hooo. The sound is very low and carries a long distance. The male voice is lower than females. Male calls are loud, rich, and deep. Female calls are longer and softer. People sometimes confuse the cooing of a dove with the hooting of an owl, but they do not sound similar. Owls also make laughing, angry, growling or guttural barks. Male owls respond easily to human imitation of their hoot.

MISCELLANEOUS COMMENTS

Great horned owls eat mammals such as rats, mice, and rabbits that cause problems for humans. Great horned owls also eat skunks, opossums, raccoons, squirrels, and other animals that also eat the eggs of grouse, pheasants and ducks.