Eagle

I

Introduction

Eagle, common name for a number of diurnal (active by day) birds of prey, some of which are the largest members of their family, which also includes buzzards, hawks, kites, and certain vultures. The name “eagle” is somewhat loosely applied, because several of the groups are not particularly closely related to one another, and some birds called hawks are larger than some called eagles.

II

Golden and Related Eagles

The golden eagle is distributed throughout most of the northern hemisphere. This is the eagle that has been regarded from ancient times as a symbol of courage and power because of its large size, superb aerial skills, and the inaccessibility of many of its nest sites, in wild and mountainous country. In Roman myths this eagle is associated with the principal deity, Jupiter. It was the emblem of certain Roman legions, of France under the Bonapartes, of Germany, and of the Russian and Austro-Hungarian empires.

The golden eagle is found in most of Eurasia (except France and its north-eastern neighbours). In North America it occurs as far south as Mexico, but it is most common in the mountainous areas of the western United States and Canada. Females attain a length of about 1 m (3 ft) from the tip of the beak to the tip of the tail, and have a wingspan of about 2 m (7 ft). Males are smaller, as is true for most of the birds of prey. A characteristic of the genus is the feathering of the legs down to the toes; in other eagles the lower part of the leg is bare and scaled, as in most birds. The body plumage is dark brown, with a distinct golden wash over the back of the head and neck, giving the species its name. The tail of adults is brown with several indistinct pale bands; that of immature birds is white with a dark brown terminal band.

Most golden eagles’ nests are built on cliff ledges, but in some areas large trees are preferred. The nest is large and coarse, built of sticks and twigs. The same nest is used from year to year, and the birds add more sticks, so that the nest may eventually be as much as 1.8 m (6 ft) in diameter and 1.5 m (5 ft) high. The usual number of eggs is two, often only one, and occasionally three. They are heavily marked with blotches and spots of various shades of brown. The diet of this species consists mainly of mammals, ranging in size from mice to deer. Birds are taken most often in the breeding season to provide tender food for the young. If live food is in short supply, golden eagles will eat carrion.

There are eight other species in the golden eagle’s genus. The smallest is the lesser spotted eagle, with a wingspan of about 1.5 m (5 ft), which migrates from central Europe to as far south as South Africa, and the booted eagle of Mediterranean countries. Bonelli’s eagle is confined mainly to Spain and Greece. The largest eagle is the wedge-tailed eagle of Australia, a mostly black bird with a wingspan of as much as 2.5 m (about 8 ft).

III

Sea Eagles

The sea eagles—whose alternate name of erne is rarely used—are not closely related to golden eagles; their nearest relatives are probably certain types of vultures. Their bills are longer and heavier than those of the golden eagles, and (in adults) are bright yellow rather than grey, and their lower legs are unfeathered. They inhabit coastal regions and the vicinity of lakes and streams, and feed mainly but not exclusively on fish. The bald eagle, the national bird of the United States, is a member of this group. It ranges widely in North America from Alaska to Florida, with the largest individuals coming from the northern parts of the range. After the breeding season the northern birds migrate southward, whereas many Florida eagles wander northward. The name “bald”, often thought to be a misnomer, does not imply a lack of feathers, but is derived from an obsolete word meaning marked with white, as in piebald. Young birds of this species lack the white head and tail of the adults, which take four to five years to attain. Compared to other eagles, the bald eagle is a relatively clumsy hunter and fisher, and for its prey relies mainly on dead or injured fish, or those that enter shallow water to spawn. It also steals fish from the osprey when the smaller bird has captured a live fish, harassing it in the air until the osprey drops the prey, whereupon the eagle snatches it.

The Eurasian counterpart of the bald eagle is the white-tailed sea eagle, which occasionally strays to Alaska. It is greyer than the bald eagle, and its head is pale but not white. The largest member of this group is Steller’s sea eagle, which inhabits coastal areas of north-eastern Asia and occasionally visits the Aleutian and Pribilof islands of Alaska. It is a blackish eagle with a wedge-shaped white tail and (in adults) a large patch of white on the shoulders.

IV

Crested and Other Eagles

Some of the largest birds of prey in the world are tropical eagles. Among the most powerful of these is the harpy eagle, which weighs about 4.8 kg (10.5 lb). As an inhabitant of lowland virgin forests from southern Mexico to northern Argentina, it has become an endangered species with the continuing loss of its habitat. It feeds principally on arboreal (tree-dwelling) mammals such as monkeys, sloths, and opossums. Its back is slate-black and its underparts are white, with a black band across the upper chest. Its pale grey head is crowned with a double crest which, when erect, gives the bird a somewhat owl-like appearance. The Eurasian counterpart of the harpy eagle, and similar to it in weight, is the Philippine or monkey-eating, eagle, the national bird of the Philippines, now found in only a few remote mountain areas of the larger islands and one of the world’s most endangered species.

A group of small and medium-sized eagles of tropical and subtropical areas of Eurasia and Africa are collectively called hawkeagles. Many have narrow elongated crests. Bushy crests are characteristic of the serpent eagles of tropical Asia, which, as the name suggests, feed predominantly on reptiles, as does the short-toed eagle of southern Europe and the Mediterranean. One of the strangest eagles is the bateleur of open country in tropical Africa. Its silhouette in flight is unique—as it has long, broad wings and an exceptionally short tail. Unlike other eagles, it feeds mostly on carrion.