The
Golden Eagle (
Aquila chrysaetos) is one of the best-known
birds of prey in the
Northern Hemisphere. It is the most widely distributed species of
eagle. Like all eagles, it belongs to the family
Accipitridae.
These birds are dark brown, with lighter golden-brown plumage on their
napes. Immature eagles of this species typically have white on the tail
and often have white markings on the wings. Golden Eagles use their
agility and speed combined with extremely powerful feet and massive,
sharp talons to snatch up a variety of prey (mainly
hares,
rabbits,
marmots and other
ground squirrels).
Golden Eagles maintain home ranges or territories that may be as large as 200 km
2 (77 sq mi). They build large
nests
in high places (mainly cliffs) to which they may return for several
breeding years. Most breeding activities take place in the spring; they
are monogamous and may remain together for several years or possibly for
life. Females lay up to four
eggs,
and then incubate them for six weeks. Typically, one or two young
survive to fledge in about three months. These juvenile Golden Eagles
usually attain full independence in the fall, after which they wander
widely until establishing a territory for themselves in four to five
years.
Once widespread across the
Holarctic, it has disappeared from many areas which are now more heavily populated by humans. Despite being
extirpated from or uncommon in some its former range, the species is still fairly ubiquitous, being present in sizeable stretches of
Eurasia,
North America, and parts of
North Africa. It is the largest and least populous of the five species of true accipitrid to occur as a breeding species in both the
Palearctic and the
Nearctic.
[2]
For centuries, this species has been one of the most highly regarded birds used in
falconry, with the Eurasian subspecies having been used to hunt and kill prey such as
Gray Wolves (
Canis lupus)
in some native communities. Due to its hunting prowess, the Golden
Eagle is regarded with great mystic reverence in some ancient, tribal
cultures. The Golden Eagle is one of the most extensively studied
species of raptor in the world in some parts of its range, such as the
Western United States and the
Western Palearctic.
Description
Subadult, note white in tail and dark neck
The Golden Eagle is a very large, dark brown raptor with broad wings,
ranging from 66 to 102 cm (26 to 40 in) in length and from
1.8 to 2.34 m (5 ft 11 in to 7 ft 8 in) in wingspan.
[3][4][5][6] This species' wingspan is the fifth largest amongst extant eagle species.
[4] In the largest race (
A. c. daphanea) males and females weigh typically 4.05 kg (8.9 lb) and 6.35 kg (14.0 lb). In the smallest subspecies,
A. c. japonica, males weigh 2.5 kg (5.5 lb) and females 3.25 kg (7.2 lb).
[7] In the species overall, males may average around 3.6 kg (7.9 lb) and females around 5.1 kg (11 lb).
[8] The maximum size of this species is a matter of some debate. Large races are the heaviest representatives of the
Aquila
genus and this species is on average the seventh-heaviest living eagle
species. The Golden Eagle ranks as the second heaviest breeding eagle in
North America,
Europe and
Africa but the fourth heaviest in
Asia.
[4][2]
For some time, the largest known mass authenticated for a wild female
was the specimen from the nominate race which weighed around 6.7 kg
(15 lb) and spanned 2.55 m (8 ft 4 in) across the wings.
[9]
American Golden Eagles are typically somewhat smaller than the large
Eurasian races, but a massive female that was banded and released in
2006 around Wyoming’s
Bridger-Teton National Forest became the heaviest wild Golden Eagle on record, at 7.2 kg (16 lb).
[10] No comprehensive range of weights are known for the largest subspecies (
A. c. daphanea).
[9]
Captive birds have been measured up to a wingspan of 2.81 m (9 ft 3 in)
and a mass of 12.1 kg (27 lb) (the latter figure was for an eagle bred
for the purposes of
falconry which tend to be unnaturally heavy), respectively.
[9] The standard measurements of the species include a
wing chord length of 52–72 cm (20–28 in), a tail length of 26.5–38 cm (10.4–15 in) and a
tarsus length of 9.4–12.2 cm (3.7–4.8 in).
[4] The
culmen reportedly averages around 4.5 cm (1.8 in), with a range of 3.6 to 5 cm (1.4 to 2.0 in) and the bill length from the
gape measures around 6 cm (2.4 in).
[11][12] The long, straight and powerful
hallux-claw
(or hind claw, the equivalent to the big toe) can range from
4.5 to 6.34 cm (1.8 to 2.50 in), being about one centimeter more than
the hallux-claw of a
Bald Eagle (
Haliaeetus leucocephalus) and a little more than one cm less than a
Harpy Eagle (
Harpia harpyja).
[13][14][15] The sexes are similar in plumage but are considerably
dimorphic
in size. Females are rather larger than males with the differences
increasing as the body size increases across the races. The large
Himalayan Golden Eagles females are about 37% heavier and nearly 9%
longer in wing length than the males of the race compared with the small
Japanese Golden Eagles where females are a relatively modest 26%
heavier and around 6% longer in wing length than males.
[7][16]
The formidable foot and talons of a Golden Eagle
Adults are primarily dark brown in color, with a paler, typically
golden color (the source of the species’ common name) on the back of the
crown and nape, and some grey on the inner-wing and tail.
[17] There are subtle differences in coloration among the races, described below. Unlike in other
Aquila species, where the
tarsal
feathers are typically of a similar color to the rest of the plumage,
the tarsal feathers of Golden Eagles tend to be paler, ranging from
light golden to white.
[7] In addition, some full-grown birds (especially in North America) have white "
epaulettes" on the upper part of each scapular
feather tract.
[2][18] The bill is dark at the tip, fading to a lighter horn color, with a yellow
cere.
[19] As in many acciptrids, the bare portion of the feet are yellow.
[4]
This species moults gradually beginning in March or April until
September or October each year. Moulting usually decreases in winter.
Moult of the contour feathers begins on the head and neck region and
process along the feather tracts in a general anterior-posterior
direction. Feathers on head, neck, back and scapulars may be replaced
annually. With large feathers of the wing and tail, moult beginning with
innermost feather and proceeds outwards in a straightforward manner
known as "descendant" moult.
[18]
The juvenile Golden Eagle is similar to the adult but tends to be darker, appearing black on the back especially in
East Asia.
Compared to adults, juveniles have a more unfaded color. Young birds
are white for about two-thirds of their tail length ending with a broad,
black terminal band.
[16] Occasionally, juvenile eagles have white patches on the
remiges
at the bases of the inner primaries and the outer secondaries, forming a
crescent marking on the wings which tend to be divided by darker
feathers.
[7][20]
Rarely, juvenile birds may have only trace amounts of white on the
tail. Compared to the relatively consistently white tail, the white
patches on the wing are extremely variable and some juveniles have
almost no white visible. Juveniles of less than 12 months of age tend to
have the most extensive amount of white to the plumage.
[18]
By their second summer, the white underwing coverts are usually
replaced by a characteristic rusty-brown color. By the third summer, the
upper-wing coverts are largely replaced by dark brown feathers, however
not all feathers moult at once giving many juvenile birds a grizzled
pattern. The tail also follows a similar pattern of maturation.
[18][20] Due to the amount of variability in different individuals, juvenile eagles cannot be reliably aged on sight alone.
[21] Many Golden Eagles still have white on the tail during their first attempt at nesting.
[22] The final adult plumage is not fully attained until the birds are between 5 and a half and 6 and a half years old.
[21]
Voice
Golden Eagles are often silent
While many accipitrids are not known for their strong voices, Golden
Eagles have a particular tendency for silence, even while breeding.
[23]
Some vocalization, however, has been recorded, and these normally are
centering around the nesting period. The voice of the Golden Eagle is
considered weak, high and shrill, even being emphatically described as
“quite pathetic” and “
puppy-like”, and as somewhat incongruous considering the formidable size and nature of the species.
[4]
Most known vocalization seem to function as contact calls between
eagles, sometimes adults to their offspring, occasionally territorial
birds to intruders and rarely between a breeding pair. In Western
Montana, nine distinct calls were noted: a
chirp, a
seeir, a
pssa, a
skonk, a
cluck, a
wonk, a
honk and a
hiss.
[24]
Flight physiology
Golden Eagle flying in dihedral with food
Golden Eagles are sometimes considered the most superlative fliers among eagles and perhaps among all raptorial birds.
[23] They are equipped with broad, long wings with somewhat finger-like indentations on the tips of the wing.
[4] Golden Eagles are unique among their genus in that they often fly in a slight
dihedral, which means the wings are often held in a slight, upturned V.
[4]
When they must engage in flapping flight, Golden Eagles appear at their
most labored but this flight method is generally less common than
soaring or gliding flights.
[7] Flapping flight usually consists of 6–8 deep wing-beats, interspersed with 2 to 3 second glides.
[7] While soaring the wings and tail are held in one plane with the primary tips often be spread.
[25] A typical, unhurried soaring speed in Golden Eagles is around 45–52 kilometers per hour (28–32 mph).
[26] When hunting or displaying, the Golden Eagle is capable of very fast gliding, attaining speeds of up to 190 km/h (120 mph).
[7][25]
When diving (or stooping) in the direction of prey or during
territorial displays, the eagle holds its wings tight and partially
closed against their body and the legs up against tail. In a full stoop,
a Golden Eagle can reach spectacular speeds of up to 240 to 320
kilometers per hour (150 to 200 mph) when diving after prey. Although
less agile and maneuverable, the Golden Eagle is apparently quite the
equal and possibly even the superior of the
Peregrine Falcon’s stooping and gliding speeds.
[2][27] This places the Golden Eagle as the one of the two fastest moving living animals on earth.
[9]
Although most flight in Golden Eagles has a purpose (i.e.
territoriality, hunting, etc.), some flights (such as those by solitary
birds or between well-established breeding pairs) seems to function
merely as acts of playfulness.
[2][23][28]
No comments:
Post a Comment