Most of the typical eagles are included under the genera Aquila and Ilaliaetus, each of which comprises from five to twenty species distributed through all countries, but perhaps most poorly represented in North America, where we have only one species of each genus, viz., the golden-eagle, Aquila chrysaetus, common to Europe, Asia, and North America, and the bald-headed eagle, Hallacius leucoce_phalus, peculiar to North America. The Old World white-tailed sea-eagle, albicilla, which very closely resembles a large and poorly colored bald-eagle, is found in Greenland, but not elsewhere in North America, though abundant in Europe and Asia and even in Kamschatka and the Aleutian Islands.
In Aquila the tarsus is leathered to the toes; in Haliaetus only about half way from heel to toes. The members of the genus Aquila are often spoken of as 'true eagles' as distinguished from the equally large but less regal Haliaeti, which are certainly more addicted to fishing, and perhaps oftener feed on carrion, but in this latter particular there is little choice. Other writers call both these genera 'true' eagles, relegating to the 'so-called eagles' the related genera Haliastur, Ilelotarsus, losaetus, and almost any hawk or buzzard of large size.
We may take as our type of the eagles the golden-eagle just referred to, one of the largest of its genus, and unfortunately far from common in America. It ranges from Mexico northward, being most abundant in mountainous regions, where it usually nests on inaccessible cliffs, and lays two or three eggs, which are commonly brown-spotted, though occasionally white like those of the bald-eagle.
On the other side of the Atlantic it ranges somewhat further south, being abundant in the Atlas mountains of northern Africa, and of common occurrence in India, and, though everywhere a mountain-loving bird, in the two last-named places, it not infrequently nests in trees. In Great Britain at one time both this and the sea-eagle were verging on extinction, owing to the bounties paid for their destruction on account of their depredations on flocks. It is now, however, not uncommon in Scotland, and in some localities there even seems to be increasing in numbers, probably owing to two causes combined, one the protection granted it by the owners of many large estates, and the other that extended to it by the shepherds and mountaineers themselves, who have learned that a large price can be obtained for its eggs, and so, after robbing a nest once each season, allow a second set of eggs to be hatched and the young to be reared. The American bird has usually been considered a variety of the Old Wofid species, and distinguished by the name canadensis. The only points, however, in which the two forms differ, are the slightly larger size and darker plumage of the American bird, the latter point being most easily recognized in the young. The adults range in length from two and one half to three feet, and the wings spread from six to seven feet.
The smallest member of the genus is the dwarf-eagle, Aquila loennata, a native of southern Europe, north Africa, and India, which measures only eighteen inches or two feet in length. Other notable species are the king-eagle, A. heliaca, of southeastern Europe and Asia, equalling the golden in size, and supposed by many to be the species once adopted as the emblem of the Roman empire; the imperial eagle, A. mogilnik, but slightly inferior to the last, and with about the same range; verreauxi, of south Africa, and the bold or wedge-tailed eagle of Australia. This latter differs from all the other members of the genus in having the long tail strongly graduated, the outer feathers being five or six inches shorter than the middle ones.
Severtzoff, in his "Fauna of Turkestan," says of the king-eagle, A. heliaca, "During summer it is found in all parts of Turkestan, but breeds only in the salt plains near Jorteck. During the breeding-season it is only found near its breedinghaunts, but frequently wanders and changes its residence during the winter. Like other eagles, it breeds only every alternate year. So soon as the young are fullgrown they commence to change; but the plumage changes very slowly. During the winter the moult is arrested, and recommences in the spring of the following year; and they never breed whilst this moult is progressing."
Among the sea-eagles, the North American bald-eagle is a familiar example, and too well known to need description. Of about the same size as the golden-eagle, it differs much from it in habits, haunting the shores of lakes and rivers, but especially the sea-shore, living mainly on fish, which it sometimes catches for itself, sometimes robs the osprey of, and probably most often finds cast up dead on the shore. The nest is most frequently placed on a high tree, but in sections where suitable trees are not to be found, it places its nest on rocky cliffs or precipitous banks. The eggs, which are laid very early in the season, are never (normally) less than two, which is the regular number, though sometimes three or four are laid. They are nearly spherical, dull white, unspotted, and average about three inches by two and three-quarters.
The finest bird of the genus is undoubtedly the northern sea-eagle, Haliaetus pelagicus, of northeastern Asia. It is readily recognized by its large size, with extremely large bill, cuneate or graduated tail (of fourteen feathers), and white thighs, shoulders, rump, and tail, the other parts being brown. The African seaeagle, II.. vocifer, is remarkable for a coloring unusual in this group. The head, neck, breast, and tail are pure white, the remainder of the under parts, including the thighs, sides of body, and under wing-coverts, deep chestnut; while the upper parts are brown or black. It is a comparatively small bird, being little more than half the size of the bald-eagle, and closely approaching in 'size the common red-tailed hawk, jButeo borealis. This is the smallest eagle of the genus unless we except the nearly related vociferoides of Madagascar, which is of the same size and with somewhat similar colors. Like the other members of the genus, these birds feed largely on fish, and are seldom found at any great distance from water.
Closely allied to Haliaetus, if indeed it is not really congeneric, is the peculiar fishing-eagle, Polioaetus ichthyaetus, of India and the East Indies generally, an eagle with almost the exact habits of the osprey (Pandion), subsisting entirely on fish, and with its external anatomy much modified to suit its requirements, its talons being much curved, very sharp, and rounded almost precisely as in that species. Two species are known.
Here may be mentioned a small group of two or three species very closely allied on the one hand to Aquila, from which, however, they are distinguished by their longer legs, and on the other to the hawk-eagles, Spizaetus and allies. The most familfar member of the group in Europe is Donelli's eagle, saetus fasciatus, a common bird of the Mediterranean region, and extending eastward to India.
