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EAGLE,
common name for a number of diurnal birds of prey, some of
which are the largest members of the family Accipitridae, which
also includes kites, hawks, buzzards, and Old World vultures. This family
is a member of the order Falconiformes. The name “eagle” is
somewhat loosely applied, as several of the groups are not particularly
closely related to one another, and some birds called “hawks” are
larger than some called “eagles.”
The golden eagle, Aquila chrysaetos, is distributed
through 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 and of France under the
Bonapartes, Germany, and the Russian and Austro-Hungarian empires.
In North America the golden eagle occurs as far south as Mexico,
but it is most common in the mountainous areas west of the western
U.S. and Canada; east of the Mississippi it is relatively rare.
Females attain a length of about 1 m (about 3 ft) from the tip of
the beak to the tip of the tail, and have a wingspread of about
2 m (about 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 eagle nests are placed 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 of the genus Aquila, all
in the Old World. The smallest is the lesser spotted eagle, A.
pomarina, with a wingspan of about 1.5 m (about 5 ft);
the eagles of this species migrate from central Europe to as far
south as South Africa. The largest is the wedge-tailed eagle, A.
audax, of Australia, a mostly black bird with a wingspan
of as much as 2.5 m (about 8.2 ft).
The sea eagles, of the genus Haliaeetus,
whose alternate name of “erne” is now chiefly
confined to crossword puzzles, are not closely related to Aquila;
their nearest relatives are probably the Old World vultures. Compared
with Aquila eagles, their bills are longer and
heavier, and (in adults) are bright yellow rather than gray, and
their lower legs are unfeathered. They inhabit coastal regions and
the vicinity of lakes and streams, and feed heavily but not exclusively
on fish. The bald eagle, H. leucocephalus, the
national bird of the U.S., 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 south, 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 relies heavily on dead or injured fish, or
those that come to 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 fish, whereupon the eagle
snatches it.
The Eurasian counterpart of the bald eagle is the white-tailed
sea eagle, H. albicilla, which occasionally strays
to Alaska. It is grayer than the bald eagle, and its head is pale
but not white. The largest member of this group is Steller’s
sea eagle, H. pelagicus, which inhabits coastal
northeastern 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.
Some of the largest birds of prey in the world are tropical eagles.
Among the most powerful of these is the harpy eagle, Harpia
harpyja, which weighs about 4.8 kg (about 10.5 lb). As
an inhabitant of lowland virgin forests from southern Mexico to
northern Argentina, it has become critically endangered with the
ongoing loss of its habitat. It feeds principally on arboreal mammals such
as monkeys, sloths, and opossums. Its back is slatey black and its
underparts are white, with a black band across the upper chest.
Its pale gray head is crowned with a double crest which, when erected,
gives the bird a somewhat owl-like appearance. The Old World counterpart
of the harpy eagle, and similar to it in weight, is the Philippine
or monkey-eating eagle, Pithecophaga jefferyi, the
national bird of the Philippines, now found in only a few remote
mountain areas of the larger islands.
A group of small and medium-sized eagles of tropical and subtropical
areas of the Old World, in the genera Hieraaetus, Spizastur,
and Spizaetus, are collectively called hawk eagles.
Many have narrow elongated crests. Bushy crests are characteristic
of the serpent eagles, genus Spilornis, of tropical
Asia, which, as the name suggests, feed predominantly on reptiles.
One of the strangest eagles is the bateleur, Terathopius ecaudatus,
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.
Eagles lay few eggs; most species hatch and rear only one
or two nestlings. Although male golden eagles will brood newly hatched
chicks, in most eagles the male’s role is to hunt for food,
which he brings to the female at the nest; she then feeds the chicks.
The female stays at or near the nest until the downy young have
begun to feather out, at which time she will resume hunting for
food for the chicks while the male’s share of this activity
diminishes. 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 rapidly, whereas in others there
is a long transition period as parental feeding tapers off.
Because eagles need a large territorial range and raise few
offspring, habitat disturbances have threatened many species even
where regulations against hunting are strictly enforced.