Golden Eagle

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 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 km2 (77 sq mi). They build large nests in cliffs and other high places 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 of its former range, the species is still widespread, 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.
For centuries, this species has been one of the most highly regarded birds used in falconry. Due to its hunting prowess, the golden eagle is regarded with great mystic reverence in some ancient, tribal cultures. It 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 ==
The golden eagle is a very large raptor, 66 to 102 centimetres (26 to 40 in) in length. Its wings are broad and the wingspan is 1.8 to 2.34 metres (5 ft 11 in to 7 ft 8 in). Golden eagles' wingspan is the fifth largest among living eagle species. Females are larger than males, with a bigger difference in larger subspecies. Females of the large Himalayan golden eagles are about 37% heavier than males and have nearly 9% longer wings, whereas in the smaller Japanese golden eagles, females are only 26% heavier with around 6% longer wings. In the largest subspecies (A. c. daphanea), males and females weigh typically 4.05 kilograms (8.9 lb) and 6.35 kg (14.0 lb), respectively. In the smallest subspecies, A. c. japonica, males weigh 2.5 kg (5.5 lb) and females 3.25 kg (7.2 lb). In the species overall, males average around 3.6 kg (7.9 lb) and females around 5.1 kg (11 lb). The maximum size of golden eagles debated. Large subspecies are the heaviest representatives of the Aquila genus and this species is on average the seventh-heaviest living eagle species. The golden eagle is the second heaviest breeding eagle in North America, Europe and Africa and the fourth heaviest in Asia. For some time, the largest known mass authenticated for a wild female was the specimen from the A. c. chrysaetos subspecies which weighed around 6.7 kg (15 lb) and spanned 2.55 m (8 ft 4 in) across the wings. American golden eagles are typically somewhat smaller than the large Eurasian species, 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 7.7 kg (17 lb). Captive birds have been measured with a wingspan of 2.81 m (9 ft 3 in) and a mass of 12.1 kg (27 lb), though this mass was for an eagle bred for falconry, which tend to be unnaturally heavy.
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 (10.4–15.0 in) and a tarsus length of 9.4–12.2 cm (3.7–4.8 in). The culmen (upper ridge of beak) reportedly averages around 4.5 cm (1.8 in), with a range of 3.6 to 5 cm (1.4 to 2.0 in). The bill length from the gape measures around 6 cm (2.4 in). The long, straight and powerful hallux-claw (hind claw) can range from 4.5 to 6.34 cm (1.77 to 2.50 in), about one centimetre longer than in a bald eagle and a little more than one centimetre less than a harpy eagle.
Adults of both sexes have similar plumage and are primarily dark brown, with some grey on the inner wing and tail, and a paler, typically golden colour on the back of the crown and nape that gives the species its common name. Unlike other Aquila species, where the tarsal feathers are typically similar in colour to the rest of the plumage, the tarsal feathers of golden eagles tend to be paler, ranging from light golden to white. In addition, some full-grown birds (especially in North America) have white "epaulettes" on the upper part of each scapular feather tract. The bill is dark at the tip, fading to a lighter horn colour, with a yellow cere. Like many accipitrids, the bare portion of the feet is yellow. There are subtle differences in colouration among subspecies, described below.
Juvenile golden eagles are similar to adults but tend to be darker, appearing black on the back especially in East Asia. They have a less faded colour. Young birds are white for about two-thirds of their tail length, ending with a broad, black band. 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 tends to be divided by darker feathers. Rarely, juvenile birds may have only traces of white on the tail. Compared to the relatively consistently white tail, the white patches on the wing are extremely variable; some juveniles have almost no white visible. Juveniles of less than 12 months of age tend to have the most white in their plumage. By their second summer, the white underwing coverts are usually replaced by a characteristic rusty brown colour. By the third summer, the upper-wing coverts are largely replaced by dark brown feathers, although not all feathers moult at once which leaves many juvenile birds with a grizzled pattern. The tail follows a similar pattern of maturation to the wings. Due to the variability between individuals, juvenile eagles cannot be reliably aged by sight alone. Many golden eagles still have white on the tail during their first attempt at nesting. The final adult plumage is not fully attained until the birds are between 5 and a half and 6 and a half years old.
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