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Owl - biology.

Publié le 11/05/2013

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Owl - biology. I INTRODUCTION Owl, common name for a group of birds of prey that mainly hunt at night. Owls have exceptional eyesight and the best hearing of all birds. Owls are found worldwide except in the Antarctic region, and they have adapted to environments ranging from arctic tundra to deserts. Scientists have named over 200 owl species, most of which live in forests. Some owls are threatened by habitat loss and human activity. Owls have long held a special fascination because of their mysterious habits and distinctive appearance. The owl is often used to symbolize wisdom, an image that dates back to ancient Greece. The owl was associated with Athena, the Greek goddess of wisdom. Other cultures, however, have seen the owl as more sinister--a symbol of death and darkness. The ancient Romans considered the owl a bad omen, a sign that some misfortune would happen. Owls have also been associated with magic and sorcery. II PHYSICAL DESCRIPTION Owls have very large eyes that are directed forward to provide a wide field (60 to 70 degrees) of binocular vision for depth perception. Owls reportedly have the best night vision of any animal and their eyes are ten times more sensitive to light than human eyes. The eyes of owls are so large that there is little room in the skull for muscles to move the eyes. Instead, owls must turn their entire heads to look sideways. Their relatively long and flexible necks permit the head to rotate up to 270 degrees, leading to the myth that owls can pivot their heads completely around. The large eyes are supported internally by a circle of bones called the sclerotic ring. Owls use their extremely acute hearing to hunt in dark conditions. In many species, the large ear openings are at different levels on each side of the skull, with the left ear higher and tilted downward. This arrangement allows owls to pinpoint the direction of a sound by comparing slight differences in timing and loudness. The round ruffs of feathers called "facial disks" on the flattened faces of owls help collect and concentrate sounds much as human ears do. Using faint sounds alone, owls can accurately judge the position of small prey on the ground from 23 m (75 ft) away. Like other birds of prey, owls have needle-sharp claws (talons) on their powerful feet, with three toes pointed forward and a fourth toe pointed backward for grasping and perching. They also have sharp-tipped hooked beaks for tearing flesh, though owls have wide mouths and often swallow small prey whole. Female owls are larger than males, but otherwise look the same with generally dull brown and grey feather patterns to help blend in with woodland environments. The snowy owl, however, is white for camouflage against snow in winter and in arctic regions. Some owls have a pair of feather tufts on their heads that resemble "ears" or "horns." These ornamental feathers help owls recognize their own species and have no function related to hearing. The wings of owls are relatively broad and short, adapted for maneuvering in low-level flight among trees rather than for soaring over open areas. Their feathers are widely spaced and have fluffy edges that muffle their flight, making owls almost perfectly silent as they approach prey. The different species of owls have distinct calls used to announce their territories. Many owls hoot. Some make whistling, wailing, or screeching sounds. Other calls and vocal noises are used to communicate with mates. Barn owls make a hissing scream. The life spans of owl species vary. Large species such as the great horned owl and the great grey owl may live 12 years or more in the wild, and longer in captivity. Barn owls generally live about two years in the wild. Some small owls may have life spans of up to 10 years in the wild. III HUNTING AND DIET Owls feed entirely on living animals, with the size of the prey matched to the size of the owl. The smallest owls may eat mainly insects while the biggest owls can reportedly catch mammals as large as hares, deer fawns, weasels, or foxes. Small rodents are the main prey for a great variety of owls. A number of owls also eat other birds. Some owls eat bats caught in the air. A few owls feed primarily on fish. Owls often swallow prey whole rather than carefully tearing off bits of flesh. Indigestible portions of their food, such as bones, hair, and feathers, are compressed and regurgitated as compact pellets. Studying the contents of pellets reveals what species the owls prey on. Most owls hunt at night. The barn owl becomes active at dusk. About a third of owl species hunt during the daytime, including the snowy owl and the northern pygmy owl. Owls generally maintain a hunting territory year round. However, some species that live in northern regions may migrate south in winter in years when food supplies are low. IV NESTING AND REPRODUCTION Owls do not build their own nests. They may reuse a nest built by an eagle or a crow, or may use a hollow in a tree. Burrowing owls nest on the ground in abandoned burrows made by other animals. They use their claws to expand the burrows and may live in colonies. Barn owls simply lay their eggs in a flat, enclosed spot high off the ground. Most owls are territorial and solitary. Males and females generally maintain separate nests and hunting territories. During breeding season, the male may seek out the female in her nest. Sometimes a male brings a freshly caught animal to the female as part of a courting ritual. Some owls such as screech owls and barn owls keep the same mate for life. Other owls only pair for a single breeding season. All owls lay white eggs. Larger species may lay from 2 to 5 eggs. Some smaller species lay up to 10 eggs. Barn owls sometimes lay as many as 12 eggs. The female incubates the eggs from about 25 to 30 days in most species. The male brings her food while she remains with the eggs. After the owlets hatch, the young remain in the nest and both parents begin to provide them with food. As the baby owls grow, their diet may be adjusted from insects to larger prey, including whole rodents. Most owlets are ready to fly and leave the nest after two months. Parental care stops and the young owls must learn to hunt on their own. V TYPES OF OWLS Scientists divide owls into two families: typical owls (Strigidae), which contains the great majority of species, and barn owls (Tytonidae). Among the largest species of typical owls are the eagle owls. They have tufts of feathers on their heads that are called "ears." The great horned owl is the only eagle owl found in the Americas. It is about 60 cm (25 in) in length with a wingspan of 1.4 m (60 in). Numerous species of eagle owls inhabit Europe, Africa, and Asia. Most widely distributed is the northern eagle owl, found from Scandinavia and Spain to Japan. It is about 71 cm (28 in) long with a wingspan of about 2m (72 in). Nearly as large and closely related to eagle owls is the snowy owl, found in North America, Europe, and Asia. Snowy owls lack ear tufts. Screech owls and scops owls are small typical owls found worldwide. Most are about 20 cm (8 in) long. Many species have prominent feather ear tufts. Researcher know much about some of these owls, such as the eastern screech owl of eastern North America, and the Eurasian scops owl, a migratory species that breeds in southern Europe east to Lake Baikal. Many related tropical species, however, remain to be studied. So-called earless owls, which lack ear tufts, include the great grey owl, the tallest owl, found in North America, Europe, and Asia. The great grey owl is up to 84 cm (33 in) long, with a wingspan of 1.5 m (60 in). Also earless are the pygmy owls, which are smaller than the screech owls. The northern pygmy owl lives in parts of western North America from Canada to the Southwest. Smallest of all owls is the elf owl of the southwestern United States and Mexico. It is 13 cm (5 in) long, and nests in woodpecker holes in large cacti. Barn owls and masked owls, along with bay owls, make up the barn owl family. They have smaller eyes and longer legs than typical owls, and are recognizable by their heart-shaped faces. Barn owls are found worldwide, including on Pacific islands where they were introduced to control rats. VI CONSERVATION About 25 percent of owl species worldwide are on the International Union for the Conservation of Nature and Natural Resources (IUCN) Red Data list with some risk of extinction in the wild. In the United States, two owls are protected under the Endangered Species Act: the northern spotted owl and the ferruginous pygmy owl. The northern spotted owl depends on old growth forests for survival, and efforts to protect the species led to restrictions on logging in areas of California, Oregon, and Washington beginning in the 1990s. The situation grew more complicated when the barred owl began to move into areas inhabited by the spotted owl. The more adaptable barred owl has begun displacing the threatened northern spotted owl in some regions. In parts of the United States local populations of owls are under pressure from habitat loss caused by urban development as well as logging. Pesticides and other chemicals also affect owls. Chemicals used to kill rodents can poison owls over time if the owls eat animals that have consumed the rodenticides. Other pesticides can affect reproduction in owls. An emerging threat to owl populations is the West Nile virus, a disease spread by mosquitoes. The disease originated in Africa and first appeared in the United States in 1999. The virus has since spread from the East Coast to the West Coast. Birds are carriers of the virus. Members of the crow family, raptors, and owls are particularly vulnerable and have a high death rate after infection. Scientific classification: Owls make up the order Strigiformes. Typical owls make up the family Strigidae, and barn owls make up the family Tytonidae. The eastern screech owl is classified as Megascops asio (also as Otus asio), and the Eurasian scops owl as Otus scops. Eagle owls make up the genus Bubo. The great horned owl is classified as Bubo virginianus, and the northern eagle owl as Bubo bubo. The snowy owl is classified as Bubo scandiacus (also as Nyctea scandiaca). The great grey owl is Strix nebulosa. The burrowing owl is now classified as Athene cunicularia (formerly Speotyto cunicularia). The elf owl is classified as Micrathene whitneyi. The common barn owl is classified as Tyto alba. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

« Among the largest species of typical owls are the eagle owls.

They have tufts of feathers on their heads that are called “ears.” The great horned owl is the only eagleowl found in the Americas.

It is about 60 cm (25 in) in length with a wingspan of 1.4 m (60 in).

Numerous species of eagle owls inhabit Europe, Africa, and Asia.

Mostwidely distributed is the northern eagle owl, found from Scandinavia and Spain to Japan.

It is about 71 cm (28 in) long with a wingspan of about 2m (72 in).

Nearly aslarge and closely related to eagle owls is the snowy owl, found in North America, Europe, and Asia.

Snowy owls lack ear tufts. Screech owls and scops owls are small typical owls found worldwide.

Most are about 20 cm (8 in) long.

Many species have prominent feather ear tufts.

Researcher knowmuch about some of these owls, such as the eastern screech owl of eastern North America, and the Eurasian scops owl, a migratory species that breeds in southernEurope east to Lake Baikal.

Many related tropical species, however, remain to be studied. So-called earless owls, which lack ear tufts, include the great grey owl, the tallest owl, found in North America, Europe, and Asia.

The great grey owl is up to 84 cm (33in) long, with a wingspan of 1.5 m (60 in).

Also earless are the pygmy owls, which are smaller than the screech owls.

The northern pygmy owl lives in parts of westernNorth America from Canada to the Southwest. Smallest of all owls is the elf owl of the southwestern United States and Mexico.

It is 13 cm (5 in) long, and nests in woodpecker holes in large cacti. Barn owls and masked owls, along with bay owls, make up the barn owl family.

They have smaller eyes and longer legs than typical owls, and are recognizable by theirheart-shaped faces.

Barn owls are found worldwide, including on Pacific islands where they were introduced to control rats. VI CONSERVATION About 25 percent of owl species worldwide are on the International Union for the Conservation of Nature and Natural Resources (IUCN) Red Data list with some risk ofextinction in the wild.

In the United States, two owls are protected under the Endangered Species Act: the northern spotted owl and the ferruginous pygmy owl.

Thenorthern spotted owl depends on old growth forests for survival, and efforts to protect the species led to restrictions on logging in areas of California, Oregon, andWashington beginning in the 1990s.

The situation grew more complicated when the barred owl began to move into areas inhabited by the spotted owl.

The moreadaptable barred owl has begun displacing the threatened northern spotted owl in some regions. In parts of the United States local populations of owls are under pressure from habitat loss caused by urban development as well as logging.

Pesticides and otherchemicals also affect owls.

Chemicals used to kill rodents can poison owls over time if the owls eat animals that have consumed the rodenticides.

Other pesticides canaffect reproduction in owls. An emerging threat to owl populations is the West Nile virus, a disease spread by mosquitoes.

The disease originated in Africa and first appeared in the United States in1999.

The virus has since spread from the East Coast to the West Coast.

Birds are carriers of the virus.

Members of the crow family, raptors, and owls are particularlyvulnerable and have a high death rate after infection. Scientific classification: Owls make up the order Strigiformes.

Typical owls make up the family Strigidae, and barn owls make up the family Tytonidae.

The eastern screech owl is classified as Megascops asio (also as Otus asio ), and the Eurasian scops owl as Otus scops .

Eagle owls make up the genus Bubo .

The great horned owl is classified as Bubo virginianus , and the northern eagle owl as Bubo bubo .

The snowy owl is classified as Bubo scandiacus (also as Nyctea scandiaca ).

The great grey owl is Strix nebulosa .

The burrowing owl is now classified as Athene cunicularia (formerly Speotyto cunicularia ).

The elf owl is classified as Micrathene whitneyi .

The common barn owl is classified as Tyto alba. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation.

All rights reserved.. »

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