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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 . 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 of 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. 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 == The golden eagle is a very large, dark brown raptor with broad wings, ranging from in length and from in wingspan. This species' wingspan is the fifth largest amongst extant eagle species.〔 In the largest race (''A. c. daphanea'') males and females weigh typically and . In the smallest subspecies, ''A. c. japonica'', males weigh and females .〔 In the species overall, males may average around and females around . 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.〔〔 For some time, the largest known mass authenticated for a wild female was the specimen from the nominate race which weighed around and spanned across the wings. 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 .〔(【引用サイトリンク】url=http://newwest.net/main/article/largest_wild_golden_eagle_captured_in_jackson_hole/ )〕 No comprehensive range of weights are known for the largest subspecies (''A. c. daphanea'').〔 Captive birds have been measured up to a wingspan of and a mass of (the latter figure was for an eagle bred for the purposes of falconry which tend to be unnaturally heavy), respectively.〔 The standard measurements of the species include a wing chord length of , a tail length of and a tarsus length of .〔 The culmen reportedly averages around , with a range of and the bill length from the gape measures around .〔(Sagip Eagle ). Gbgm-umc.org. Retrieved on 2012–08–22.〕〔(【引用サイトリンク】title=Birds of North America Online—Birds of North America Online )〕 The long, straight and powerful hallux-claw (or hind claw, the equivalent to the big toe) can range from , 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''). 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.〔〔 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.〔 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.〔 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 color, with a yellow cere. As in many acciptrids, the bare portion of the feet are yellow.〔 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.〔 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.〔 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.〔 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.〔 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.〔〔 Due to the amount of variability in different individuals, juvenile eagles cannot be reliably aged on 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Golden eagle」の詳細全文を読む スポンサード リンク
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