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
booted eagles.
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.
Classification:
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Aves
Order: Falconiformes
Families: Accipitridae
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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