The eagles of the world are swift, powerful
birds of prey long admired for their power, ferocity,
and regal bearing. They range in size from
the great Philippine eagle (Pithecanthropos jefferyi)
of the Philippines andNewGuinea to the Nicobar
serpent-eagle (Spilornis klossi), which occurs only
on the Great Nicobar Island off the coast of Malaysia,
and is smaller than many hawks.
In the strict taxonomic sense, the term "eagle"
is a generic term applied to any large, swift, and
powerful bird or group of birds of prey. All are
characterized by a large, hooked bill, keen vision
(called "eagle-eyed sight"), and long, broad wings
for lifting prey. The name "eagle" was originally
applied to the largest birds of prey found in the
northern hemispheres. The discovery of many
species of tropical eagles that are smaller than
some hawk species removed the eagle as the king
of birds, at least in size. Furthermore, the four
groups of birds of prey that bear the name eagle
are apparently not very closely related; some are
more similar to harriers, others to kites, and still
others to buteo hawks.
Taxonomically, all eagles are placed in the
avian order Falconiformes, which is split into two
families, the slimmer and swifter falcons in the
family Falconidae and the others-the harriers,
kites, accipiters, and eagles-in the family Accipitrinae.
The four groups of eagles include the sea
eagles, snake or serpent eagles, crested eagles, and
The Fish Eagles
The eleven species of sea and fish eagles seem mostly closely related to the kites. They occur along all the world's oceans and inland along large lakes and waterways, being absent only from Latin America. All have bare legs and show white in their heads or backs. Two of the most familiar and most widespread of the sea eagles include the bald eagle (Haliaetus leucocephalus) of North America and the European sea eagle (Haliaetus albicilla) of Eurasia. The largest is the Steller's sea eagle (Haliaetus pelagicus), which has an eight-foot wingspan and can weigh fifteen pounds. These powerful eagles feed mainly on live or dead fish but are capable of taking sea calves. The smallest fish eagle is the fish and crab-eating Madagascar fish eagle (Haliaetus vociferoides), which is now confined to the northwest coast of Madagascar. Ecologically, sea eagles often build large stick nests in trees, in sea stacks, or on ledges. Fish and offal are dietary mainstays, along with an occasional gull or other water bird. They scavenge carrion along beaches, waterways, and offshore islands. Some are kleptoparasites that pirate food from other birds such as the osprey. Sizable numbers of bald eagles winter along the coasts of the Pacific Northwest. Notable wintering concentrations also occur in the Wasatch front range of the Rockies, where their food is mostly jackrabbits and other medium-sized mammals. Because of the dietary mainstay of fish, the sea and fish eagles have proven most susceptible to chlorinated hydrocarbon pollution, which accumulates in their tissues and reduces nesting success and productivity. Several are considered threatened or endangered, although captive breeding programs have successfully led to the recovery of the bald eagle. Included in this group is the vulturine fish eagle (Gypohierax angolensis) of southern Africa, which feeds on the pericarp of oil palm nuts along with some crabs and fish. Some authorities prefer to regard this species separately from the bald eagle and rename it the palm-nut vulture.
The Snake and Serpent Eagles
The fifteen species of snake and serpent eagles are a primitive group that have long wings and bare legs as an adaptation for killing venomous snakes. They belong to the subfamily Circaetinae andmay be allied to kites. All are OldWorld species; most live in Africa and southeast Asia, but one, the short-toed snake eagle (Circaetus gallicus) occurs as a breeding species across much of Europe. Serpent eagles are generally large, brown or grayish eagles with yellow eyes, and short toes adapted for killing reptiles. They feed almost entirely on snakes, lizards, and amphibians, mainly frogs. Serpent eagles hunt entirely by the perch-andwait method and most have little difficulty in killing even the larger venomous snakes of Africa and southeast Asia. They are not immune to venom, but rather depend on quickness to avoid being fatally bitten. The European serpent or short-toed eagle (Circaetus gallicus) is also included in this group, although it seems more closely related to harriers. Another aberrant form is the dark, long-winged bateleur (Terathopius ecudatus) of central and southern Africa. Unlike the other snake eagles, the bateleur hunts for small mammals and reptiles across the African plains and savanna in low, searching flights, attacking in tight downward spirals. Groups of immature bateleurs gather to feed on abundant insects, especially at termite mounds when alates emerge.
The Crested Eagles
A third eagle group consists of four species of buzzardlike eagles, which are closely related to the buteo hawks and sometimes grouped with them in the subfamily Buteoninae. These include the largest and most powerful birds of prey in the world, the huge harpy and crested eagles and their relatives such as the harpy eagle (Harpya harpyja) of South America and the great Philippine eagle of the Philippines and New Guinea. These large to very large raptors can take monkeys and other medium-sized and larger mammals of the tropical rain forests.
Booted or True Eagles
The largest eagle group is the "booted" or aquiline eagles, which consists of thirty-three species found worldwide. Sometimes placed in the subfamily Aquilinae, all are large and some are very large, powerful birds of prey. They differ from all other eagles in having a fully feathered tarsus down to their toes. Booted eagles are more common in the Old World, but several species, such as the golden eagle (Aquila chrysaetos), are very widely distributed. The booted eagles also include many small forest species, such as the spizaetus species of Asia and South America. Many of these forest eagles have shorter wings and long tails for hunting birds and mammals within the triple-tiered forest canopy. Most booted eagles are entirely carnivorous, taking a wide variety of vertebrates, especially medium-sized mammals and birds. The largest species, such as the Siberian golden eagle (a subspecies of the golden eagle) take wolves, foxes, and other large mammals. More specialized booted eagles include the black eagle (Ictinateus malayensis) of southeast Asia, which regularly robs nests of eggs and young, and the tawny eagle (Aquila rapax) of Africa and India, which seems to consume everything from termites to carrion up to dead elephants.
Conservation and Economic Importance of Eagles
Even after decades of environmental education, humans still remain the greatest threat to the eagles of the world. Many eagles are shot each year by hunters and sportsman who prefer live target practice. As with other birds of prey, some eagles are hunted for the taxidermy market, a few are taken for falconry, and some are captured as part of the lucrative international trade in zoo specimens, despite the fact that eagles are protected in most countries of the world. Because of their position at the top the food chain, eagles accumulate pesticides and industrial wastes in their tissues, which can reduce nesting success and endangers the life of the eagle. Many toxic chemicals have been found in the eagles of the world, but the fish-eating eagles are most at risk. Eagles need comparatively large home ranges and are constantly at risk fromhabitat destruction and fragmentation. The rapid demise of tropical rain forests places tropical eagles in the greatest risk. Several eagles are listed as endangered or threatened species in many areas of their range. Conservation efforts have included protective legislation, along with recovery programs that included captive breeding, nesting platforms, and reintroduction programs. Both the bald eagles and the white-tailed sea eagle (Haliaetus albicilla) in Scotland have benefitted from extensive and expensive recovery efforts. Conservation programs continue to target the protection of harpy eagles in Latin America and the great Philippine eagle of the Philippine Islands.
Subfamilies: Buteoninae, CircaГ«tinae
Genus and species: Twenty-one genera and fiftythree species, including Haliaetus leucocephalus (bald eagle), Aquila chysaetos (golden eagle), Harpia harpyja (harpy eagle), Haliaetus pelagicus (Steller's sea eagle)
Geographical location: All continents except Antarctica
Habitat:Woods and woodland edges, grasslands, near water for fish-eating species
Gestational period: Thirty to forty-five days, depending on species
Life span: Twenty to thirty years in the wild; up to fifty years in captivity
Special anatomy: Talons; exceptionally keen eyesight; strong legs; sharp, hooked bills
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