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The eagle is a diverse group of about 55 species of flesh-eating diurnal birds of prey that occur on all continents except Antarctica.
Large, spectacular eagles (especially the sea eagles, harpies, and large booted eagles) are becoming rare. They are killed by farmers and gamekeepers, who shoot them or put out poisoned carrion as bait. They are also in demand by falconers, zoos, and trophy collectors. In addition, the reproductive success of eagles may be impaired by pesticide poisoning. These artificial pressures, plus natural mortality and the eagles' low reproduction rate, place many species in serious danger of extinction.
Description and Behavior of Eagles
Eagles vary in size. Ayres' eagle (Hieraetus dubius) is 16 inches long, while the harpy (Harpia harpyja), the monkey-eating eagle (Pithecophaga jefjeryi), and Steller's sea eagle (Haliaeetus pelagicus) are 36 to 40 inches long, among the largest of flying birds.
Eagles have long, massive, hooked bills and powerful toes with long, curved claws. Their eyes, although located laterally, are directed forward, thus allowing good binocular depth perception. Their wings are broad, and their breast muscles are powerfully developed. Most species are various shades of brown, black, or gray, but some are white or streaked on the underside or have light markings on the head, shoulders, wings, or tail.
The relative length of an eagle's wings and tail and the covering of its legs vary with the habitat and food habits of the species. Species that inhabit forests generally have relatively short wings and long tails that permit them to maneuver among the trees. Open country eagles, on the other hand, have relatively long wings enabling them to soar in search of prey. Species that feed mostly on birds or mammals have feathered tarsi (lower parts of the leg), while snake and fish eaters have unfeathered, heavily-scaled tarsi and rough-soled toes that allow them to get a firm grip on slippery prey.
Most eagles hunt while soaring although some species watch for their prey from a high perch. Feeding territories are very large, up to 16 square miles for large species that may range great distances for food. Eagles usually dive at their victims at an oblique angle and rely on surprise and strength rather than speed or agility. They capture a variety of live vertebrates, but most also take some carrion and are not above robbing other predators. The eagle usually captures its prey on the ground and may then carry it off to eat it elsewhere.
Reproduction and Life Cycle of the Eagle
Eagles nest both on seacoasts and on inland mountains, usually in tall trees or in high cliffs. The nest is a massive structure of sizable sticks lined with leaves and grass. Eagles may use the same nest for many years, adding to it each year; in fact, one nest in Ohio was used for 36 years and weighed almost 1 ton.
Eagles lay only one or two light brown eggs, spotted and splotched with black. Both parents incubate the eggs for relatively long periods, up to 49 days in the larger species. Both parents feed the downy young, which remain in the nest as long as 130 days before fledging. In the larger eagle species the entire reproductive cycle may last more than 12 months, so that successful breeding may take place only once every other year. Although eagles are slow to reach reproductive age, they are long-lived.
Kinds of Eagles
Eagles do not constitute a single natural unit of classification. They are classified, along with kites, hawks, Old World vultures, and harriers, in the family Accipitridae of the order Falconiformes. Eagles are divided into four groups: sea and fish eagles (subfamily Milviinae), serpent eagles (subfamily Circaetinae), harpies and booted (or true) eagles (subfamily Accipitrinae).
Sea and Fishing Eagles. Sea and fishing eagles are very large species found on seacoasts or inland waters throughout most of the world. They have massive bills, scaled tarsi, and wedgeshaped tails in most species. They feed largely by diving at fish near the surface, but they also take mammals, birds, and reptiles, and they do feed on carrion. Sea and fishing eagles include the American bald eagle (Haliaeetus leucocephalus), the European white-tailed sea eagle (H. albi-cilla), Steller's sea eagle (H. pelagicus) of northeast Asia, the tropical African fish eagle (H. vocifer), and the freshwater fishing eagles (Ichthyophaga) of southern Asia.
Serpent Eagles. Serpent eagles, which are medium-sized and stocky, prey on reptiles. They are found only in the Old World and include the widespread harrier eagles (Ciraetus) of Africa, Asia, and southern Europe, the long-tailed serpent eagles (Dryotriorchis and Eutriorchis) of the rain forests of central Africa and Madagascar, and the crested serpent eagles of southeast Asia (Spilornis). In serpent eagles the head and neck are thickly feathered, and the legs and short toes are armored- adaptations that help the eagles in capturing their dangerous and elusive prey. Serpent eagles inhabit open and lightly forested country where they soar for long periods or watch for potential prey from high perches. They kill a snake by crushing its head in their bill and then swallow it whole.
The chunky, black and chestnut batleur (Terathopius ecaudatus), found over the grasslands and forests of Africa, is the most striking and unusual species of the serpent eagle group. The batleur has remarkably long wings and almost no tail. Its face has bare, bright red skin. In flight the batleur eagle rocks from side to side and performs acrobatics. When it dives for prey, it is fast and noisy.
Harpies. The harpies include four huge, broad-winged, long-tailed eagles that inhabit the tropical rain forests of New Guinea, the Philippines, and northern South America. The most spectacular harpy is the rare monkey-eating eagle (Pithecophaga jefferyi) of the Philippines. It has a ruff of pointed erectile feathers around its face, a narrow highly arched bill, massive feet, and sharp talons capable of tearing apart monkeys, dogs, pigs, or poultry. The harpy eagle (Harpia harpyja) of South America, similar to the monkey-eating eagle, preys on Capuchin monkeys, sloths, and large macaw parrots. Both species nest in very high trees, and mounds of prey bones often accumulate under the nests.
Booted Eagles. Booted eagles (Aquila, Hieraetus, Spizaetus, and related genera) are a cosmopolitan group of eagles whose legs are feathered to the toes. Several booted eagles, especially the small crested eagles (Spizaetus) in Africa, have elongated crown feathers. The trim, graceful Old World hawk eagles (Hieraetus) are long-winged, open country bird predators. The true eagles (Aquila) hunt in open country even if they nest in forests. They include the holarctic golden eagle (Aquila chrysaetus) and the Eurasian imperial eagle (A. helica). The true eagles are dark brown or black with golden or white feathering on the head, nape, shoulders, and base of the tail. They fly low often over open countryside hunting for birds and small mammals. They also often harass other birds to give up their own prey, and they eat carrion.
The Eagle in Symbolism
The grandeur of eagles has inspired men since the Stone Age (Paleolithic) when drawings of eagles first appeared in European caves. Eagles symbolize power, courage, freedom, and immortality and have long been used as national, military, and heraldic emblems and as symbols in religion.
The single or double-headed eagle served as an emblem of the might and unity of empire for Belshazzar of Babylon, the Caesars, Charlemagne, many Holy Roman and Byzantine emperors, Napoleon, the Russian czars, and many Austrian emperors. An eagle devouring a serpent on the national seal of Mexico symbolizes the triumph of good over evil. In 1782 the United States adopted as the central motif of the seal of the United States a spread-winged bald eagle brandishing the arrows of war and the olive branch of peace to represent the strength and liberty of the nation. Eagles also appeared on the coins of many countries; the U.S. $10 gold piece had an eagle emblem. The heraldic eagle, an emblem of victory, courage, and royalty, appeared in Sumer-ian, Persian, and Egyptian battle ensigns and on the standard ("aquila") of the Roman legion.
In many ancient religions the eagle symbolized the protective strength of the deities and was the companion of the chief gods. Some North American Indians used the eagle as a symbol of ancestral immortality on their totem poles. In Hebrew and Christian religions the eagle represents the flight of the soul to heaven and the fulfillment of the messianic promise.