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Eagle - biology.

Publié le 11/05/2013

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Eagle - biology. I INTRODUCTION Eagle, large bird of prey that is active during the daytime. Like other birds of prey, such as hawks and vultures, eagles hunt, kill, and eat other animals. Eagles are found throughout the world except in Antarctica and on some remote ocean islands. Only two kinds of eagles live in North America: the golden eagle and the bald eagle. Among the largest eagles in the world are the harpy eagle of Latin America and the Philippine eagle of Asia. These birds have wingspans as great as 2.5 m (8 ft) and weigh as much as 9 kg (20 lbs). In most eagle species, the female is slightly larger than the male. The word eagle comes from the ancient Roman name for the golden eagle, aquila. This eagle has been regarded from ancient times as a symbol of courage and power because of its large size, superb flying skills, and its unreachable nest sites in remote, mountainous country. In Roman myths the golden eagle is associated with the principal god, Jupiter. It was the emblem of certain Roman military legions, of France under Napoleon, of Germany, and of the Russian and Austro-Hungarian empires. In 1782 the bald eagle was adopted for the emblem of the United States as a symbol of strength and freedom. II CHARACTERISTICS OF EAGLES Eagles are characterized by their stout legs, strong feet with sharp talons (claws), and a hooked bill that is nearly as long as their head. They have large, broad, strong wings and a broad tail that in flight is spread like a fan. The broad wings enable eagles to soar gracefully through the air. To conserve energy they flap their wings as little as possible, gliding and using thermals--rising columns of warm air--to gain height. Eagles can reach speeds up to 100 km per hour (60 mph), but they usually fly more slowly to use less energy. They can dive for prey at speeds greater than 160 kph (100 mph). Eagles have extremely sharp eyesight and can spot prey from a great distance. Respect for the eagle's keen eyesight is conveyed by the expression eagle eye. The various kinds of eagles prey on mammals, reptiles, or fish. They may swoop low to snatch prey with their feet, or make a direct downward dive onto the prey. The eagle kills its prey with its strong feet and talons, with which it can squeeze the life from the captured animal, and it rips the flesh from its prey with a large, curved bill. Eagles have a lifespan of about 20 to 30 years in the wild, though some species live even longer. Eagles in captivity can live more than 40 years. Male and female eagles are thought to form lifelong pair bonds. Some eagle species perform spectacular flight displays during courtship. They may lock talons high in the sky and tumble together through the air, separating just before they reach the ground. Eagles build nests largely of sticks and twigs, which they place in layers. They may return to the same nest year after year, adding new materials to the old nest. Over time eagle nests can become enormous, measuring more than 3 m (10 ft) high and more than 3 m (10 ft) across and weighing more than a ton. The female eagle generally lays one or two eggs. She sits on the eggs, while the male hunts and brings her food. Although male golden eagles will brood (cover and keep warm) newly hatched chicks, in most eagles the male's role is to hunt for food. He brings food to the female at the nest, and she then feeds the chicks. The female stays at or near the nest until the downy young have begun to grow feathers. At this time she starts hunting for food for the chicks while the male does less of this work. After the young are fully grown, they remain near the nest for a time while still being fed by the parents. In some species the young become independent quite soon, whereas in others there is a long transition period as the parents do less and less feeding. Eagles do not nest close to one another, and they need a large territory for hunting. Generally, the larger the eagle, the larger its prey and the larger the territory it seeks to defend. When too many nests appear in an area, fights may break out among the occupants. Because eagles raise so few offspring and because of their territorial requirements, habitat disturbances, such as water pollution, the development of waterfronts, and the destruction of forests, have threatened many eagle species. See Endangered Species. III KINDS OF EAGLES Eagles belong to a large family of birds that also includes kites, hawks, buzzards, and certain vultures. There are about 60 different species of eagles and no widely accepted system of classifying them. Some experts classify eagles by prominent features or habits into four loose groups: booted or true eagles, sea or fish eagles, forest eagles, and snake or serpent eagles. The booted eagles have feathered legs in contrast to the bare and scaled legs of eagles in the other groups (and of most other birds). Sea eagles, such as the bald eagle, feed mainly on fish. Most forest eagles inhabit tropical rain forests. As their name suggest, snake eagles feed primarily on snakes. IV GOLDEN EAGLES AND OTHER BOOTED EAGLES The golden eagle is distributed through most of the northern hemisphere, in North America, Europe, Asia, and Africa. In North America they are most common in the mountainous areas and the prairies of the western United States and Canada. Golden eagles are found as far south as Mexico. Dark brown or blackish-brown plumage covers the bodies of golden eagles, with a layer of golden feathers on the back of the head and neck. This golden plumage gives the bird its name. Female golden eagles grow about 1 m (about 3 ft) long from the tip of the beak to the tip of the tail. They have a wingspread of about 2 m (about 7 ft). Males are smaller, as is true for most birds of prey. The birds' legs and feet are feathered down to the toes. The tail of adults is brown with several indistinct pale bands; that of immature birds is white with a dark brown band at the end. Most golden eagles build their nests on cliff ledges, but in some areas they prefer to nest in large trees. Like other eagles they build large, coarse nests of sticks and twigs. The female usually lays two eggs, but she may lay only one or, on occasion, three. The eggs are heavily marked with blotches and spots of various shades of brown. Golden eagles feed mainly on small mammals, especially mice, larger rodents, and rabbits, although they can kill mammals as large as deer. They also eat reptiles and birds. If live food is in short supply, golden eagles will eat carrion (dead animal flesh). When hunting, they usually soar in low over their prey. There are a number of other species in the golden eagle's genus, Aquila. All of them are found in the Eastern Hemisphere. The smallest is the lesser spotted eagle, with a wingspan of about 1.5 m (about 5 ft); it migrates from central Europe to as far south as South Africa. The largest is the wedge-tailed eagle of Australia, a mostly black bird with a wingspan of as much as 2.4 m (about 8 ft). A group of small to medium-size booted eagles, known collectively as hawk-eagles, are found in many parts of the world. V BALD EAGLES AND OTHER SEA EAGLES Sea eagles inhabit coastal regions and the vicinity of lakes and streams, and feed heavily but not exclusively on fish. The bald eagle, the national bird of the United States, is a member of this group found only in North America. It is named for its snow-white head. However, the name bald does not refer to a lack of feathers but comes instead from an outdated word meaning marked with white, as in piebald. The adult bald eagle is blackish brown, with a white head and tail. Its bill, legs, and feet are bright yellow. The bill, which is longer and heavier than the gray bill of golden eagles, is useful for piercing the skin of fish. Bald eagles vary in size. Most of them measure from about 75 to 100 cm (about 30 to 40 in) in length, with a wingspan of 1.8 to 2.3 m (6 to 7.5 ft). The bald eagle is the second-largest bird of prey in North America. Only the California condor is larger. Compared with other eagles, the bald eagle is a relatively clumsy hunter and fisher. The birds generally hunt and kill on their own only when easier alternatives fail. For prey they rely partly on dead or injured fish, or on fish such as salmon that come to shallow water to spawn. Bald eagles also steal fish from smaller birds, especially the osprey. When the osprey has captured a live fish, the eagle harasses the bird in the air until it drops the fish, whereupon the eagle snatches the food. Scales on the feet of bald eagles help them hang onto slippery fish while they fly back to their nests. Bald eagles perch in trees for hours, watching for opportunities to feed. Female bald eagles usually lay two eggs, which take about 35 days to hatch. The young remain in the nest for 10 to 13 weeks before they fledge (fly from the nest). Young bald eagles lack the white head and white tail of the adults, which take four to five years to attain. Bald eagles have a wide range: from Alaska and Canada in the north to Florida and Mexico in the south. The birds tend to breed in the northern part of their range and to winter along ocean coasts, large rivers, or in the southern part of their range. Bald eagles were once abundant in North America, but their numbers declined dramatically during the mid- to late 20th century as a result of hunting and the use of pesticides in agriculture. Pesticides, especially DDT, entered the water and then the fish that the eagles ate. As a result of eating the poisoned fish, the female laid eggs with shells so thin that they cracked and broke while she sat on the nest. In 1973 the U.S. government banned the use of DDT, and the same year listed the bald eagle as an endangered species under the Endangered Species Act of 1973. The number of bald eagles in the United States has since climbed. But loss of habitat continues to threaten the birds. In 2007 the U.S. government removed the bald eagle from the list of endangered and threatened species. The counterpart of the bald eagle in Europe and Asia is the white-tailed sea eagle, a fish-eating eagle with a gleaming white tail. The birds occasionally stray to Alaska. The white-tailed sea eagle is grayer than the bald eagle, and its head is pale but not white. The largest of the sea eagles is Steller's sea eagle, which inhabits the coasts of eastern Siberia and northern Japan. The bird has a wingspan of 2.2 to 2.5 m (about 7 to 8 ft). This striking black eagle has a wedge-shaped white tail and, in adults, a large patch of white on its shoulders and legs. VI HARPY EAGLES AND OTHER FOREST EAGLES Some of the largest birds of prey are eagles that live in tropical forests. Among the most powerful of the forest eagles is the harpy eagle. The female's weight of 6.3 to 9 kg (14 to 20 lbs) makes it the heaviest bird of prey in the world. An inhabitant of forests from southern Mexico to northern Argentina, it has become threatened as a result of the ongoing loss of its habitat. The harpy eagle was named after the mythical Harpy, a flying monster from Greek mythology that was half woman and half predatory bird. Feathers on the top of the harpy eagle's pale gray head form a large, raised crest when the bird feels threatened and give it a somewhat owl-like appearance. The back of the harpy eagle is slate black, and its underparts are white, with a black band across the upper chest. The harpy eagle's legs are thick and its curved talons grow 13 cm (5 in) long. The birds use the talons to kill their prey--mainly forest mammals such as monkeys, sloths, and opossums. The Asian counterpart of the harpy eagle, and similar to it in weight, is the Philippine eagle, also known as the monkey-eating eagle. The national bird of the Philippines, it is now found in only a few remote mountain areas of that country's larger islands and is among the rarest birds on Earth. As its nickname suggests the Philippine eagle eats monkeys, but it feeds on many other forest animals, as well, including lemurs, squirrels, lizards, and snakes. VII SNAKE EAGLES Snake eagles feed primarily on reptiles. Strong scales on their legs protect the eagles from snakebite as they grasp their prey. One of the most interesting snake eagles is the bateleur of Africa, named from a French word meaning "acrobat." The name refers to the spectacular aerial displays of the mating birds. Bateleurs inhabit open woodlands and savannas in tropical Africa. Their silhouette in flight is unusual, as they have long, broad wings and an exceptionally short tail. Unlike other eagles, the bateleur feeds mostly on carrion. Bushy crests are characteristic of snake eagles of tropical Asia, such as the crested serpent eagle. Scientific classification: Eagles belong to the family Accipitridae of the order Falconiformes. The golden eagle is classified as Aquila chrysaetos, the lesser spotted eagle as Aquila pomarina, and the wedge-tailed eagle as Aquila audax. The bald eagle is classified as Haliaeetus leucocephalus, the white-tailed sea eagle as Haliaeetus albicilla, and Steller's sea eagle as Haliaeetus pelagicus. The harpy eagle is classified as Harpia harpyja, the Philippine or monkey-eating eagle as Pithecophaga jefferyi, and the bateleur as Terathopius ecaudatus. Contributed By: William Beebe Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

« States, is a member of this group found only in North America.

It is named for its snow-white head.

However, the name bald does not refer to a lack of feathers but comes instead from an outdated word meaning marked with white, as in piebald. The adult bald eagle is blackish brown, with a white head and tail.

Its bill, legs, and feet are bright yellow.

The bill, which is longer and heavier than the gray bill of golden eagles, is useful for piercing the skin of fish. Bald eagles vary in size.

Most of them measure from about 75 to 100 cm (about 30 to 40 in) in length, with a wingspan of 1.8 to 2.3 m (6 to 7.5 ft).

The bald eagle isthe second-largest bird of prey in North America.

Only the California condor is larger. Compared with other eagles, the bald eagle is a relatively clumsy hunter and fisher.

The birds generally hunt and kill on their own only when easier alternatives fail.

Forprey they rely partly on dead or injured fish, or on fish such as salmon that come to shallow water to spawn.

Bald eagles also steal fish from smaller birds, especially theosprey.

When the osprey has captured a live fish, the eagle harasses the bird in the air until it drops the fish, whereupon the eagle snatches the food.

Scales on thefeet of bald eagles help them hang onto slippery fish while they fly back to their nests.

Bald eagles perch in trees for hours, watching for opportunities to feed. Female bald eagles usually lay two eggs, which take about 35 days to hatch.

The young remain in the nest for 10 to 13 weeks before they fledge (fly from the nest). Young bald eagles lack the white head and white tail of the adults, which take four to five years to attain. Bald eagles have a wide range: from Alaska and Canada in the north to Florida and Mexico in the south.

The birds tend to breed in the northern part of their range andto winter along ocean coasts, large rivers, or in the southern part of their range.

Bald eagles were once abundant in North America, but their numbers declineddramatically during the mid- to late 20th century as a result of hunting and the use of pesticides in agriculture.

Pesticides, especially DDT, entered the water and thenthe fish that the eagles ate.

As a result of eating the poisoned fish, the female laid eggs with shells so thin that they cracked and broke while she sat on the nest.

In1973 the U.S.

government banned the use of DDT, and the same year listed the bald eagle as an endangered species under the Endangered Species Act of 1973.

Thenumber of bald eagles in the United States has since climbed.

But loss of habitat continues to threaten the birds.

In 2007 the U.S.

government removed the bald eaglefrom the list of endangered and threatened species. The counterpart of the bald eagle in Europe and Asia is the white-tailed sea eagle, a fish-eating eagle with a gleaming white tail.

The birds occasionally stray to Alaska.The white-tailed sea eagle is grayer than the bald eagle, and its head is pale but not white.

The largest of the sea eagles is Steller’s sea eagle, which inhabits the coastsof eastern Siberia and northern Japan.

The bird has a wingspan of 2.2 to 2.5 m (about 7 to 8 ft).

This striking black eagle has a wedge-shaped white tail and, in adults,a large patch of white on its shoulders and legs. VI HARPY EAGLES AND OTHER FOREST EAGLES Some of the largest birds of prey are eagles that live in tropical forests.

Among the most powerful of the forest eagles is the harpy eagle.

The female’s weight of 6.3 to9 kg (14 to 20 lbs) makes it the heaviest bird of prey in the world.

An inhabitant of forests from southern Mexico to northern Argentina, it has become threatened as aresult of the ongoing loss of its habitat. The harpy eagle was named after the mythical Harpy, a flying monster from Greek mythology that was half woman and half predatory bird.

Feathers on the top of theharpy eagle’s pale gray head form a large, raised crest when the bird feels threatened and give it a somewhat owl-like appearance.

The back of the harpy eagle is slateblack, and its underparts are white, with a black band across the upper chest.

The harpy eagle’s legs are thick and its curved talons grow 13 cm (5 in) long.

The birdsuse the talons to kill their prey—mainly forest mammals such as monkeys, sloths, and opossums. The Asian counterpart of the harpy eagle, and similar to it in weight, is the Philippine eagle, also known as the monkey-eating eagle.

The national bird of the Philippines,it is now found in only a few remote mountain areas of that country’s larger islands and is among the rarest birds on Earth.

As its nickname suggests the Philippineeagle eats monkeys, but it feeds on many other forest animals, as well, including lemurs, squirrels, lizards, and snakes. VII SNAKE EAGLES Snake eagles feed primarily on reptiles.

Strong scales on their legs protect the eagles from snakebite as they grasp their prey.

One of the most interesting snake eaglesis the bateleur of Africa, named from a French word meaning “acrobat.” The name refers to the spectacular aerial displays of the mating birds.

Bateleurs inhabit openwoodlands and savannas in tropical Africa.

Their silhouette in flight is unusual, as they have long, broad wings and an exceptionally short tail.

Unlike other eagles, thebateleur feeds mostly on carrion.

Bushy crests are characteristic of snake eagles of tropical Asia, such as the crested serpent eagle. Scientific classification: Eagles belong to the family Accipitridae of the order Falconiformes.

The golden eagle is classified as Aquila chrysaetos, the lesser spotted eagle as Aquila pomarina, and the wedge-tailed eagle as Aquila audax. The bald eagle is classified as Haliaeetus leucocephalus, the white-tailed sea eagle as Haliaeetus albicilla, and Steller’s sea eagle as Haliaeetus pelagicus. The harpy eagle is classified as Harpia harpyja, the Philippine or monkey-eating eagle as Pithecophaga jefferyi, and the bateleur as Terathopius ecaudatus. Contributed By:William BeebeMicrosoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation.

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