Description
The Golden Eagle is a large, dark brown raptor with broad wings. Its size is variable: it ranges from 66 to 102 cm (26 to 40 in) in length and it has a typical wingspan of 1.8 to 2.34 m (5.9 to 7.7 ft). In the largest race (A. c. daphanea) males and females weigh 4.05 kg (8.9 lb) and 6.35 kg (14.0 lb). In the smallest subspecies (A. c. japonensis), the sexes weigh, respectively, 2.5 kg (5.5 lb) and 3.25 kg (7.2 lb). In the species overall, males average around 3.6 kg (7.9 lb) and females average around 5.1 kg (11 lb). The maximum size of this species is a matter of some debate, although the normal upper weight limit for a large female is around 6.8 kg (15 lb) and large races are the heaviest representatives of the Aquila genus. Captive birds have been measured up to a wingspan of 2.81 m (9.2 ft) and a mass of 12.1 kg (27 lb) (the latter figure was for an eagle bred for the purposes of falconry). 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). 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 from the gape measures around 6 cm (2.4 in). The sexes are similar in plumage but are considerably dimorphic in size, with females rather larger than males. Adults are primarily brown, with a pale gold color on the back of the crown and nape, and some grey on the wings and tail. Tarsal feathers range from white to dark brown. In addition, some birds 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.
Juveniles have a darker, unfaded color, white patches in the remiges which may be divided by darker feathers, and a large amount of white on the tail with a black terminal band. Occasionally upper wing feathers of juveniles are also white, or birds lack white on the wing entirely. As the bird ages, the amount of white on wings and tail diminishes, and adult plumages is usually acquired by the fifth year.
Size readily distinguishes this species from most other raptors when it is seen well. Most other raptors are considerably smaller, including Buteo hawks which are perhaps most similar to the Golden Eagle in structure among smaller raptors. Buteos are also usually distinctly paler below. Only some Old World vultures and the California Condor (Gymnogyps californianus) (among the other raptorial birds this eagle co-exists with) are distinctly larger, with longer, broader wings, typically held more evenly, and often have dramatically different color patterns. Compared to Haliaeetus eagles, the Golden is usually longer-tailed and is distinctly smaller-headed, with broad wings that are more hawk-like and less plank-like in shape. Whereas more Haliaeetus eagles are heavily streaked in their juvenile phase, the Golden has a more solidly golden-brown coloration. Distinguishing it from other Aquila eagles in Eurasia is a greater identification problem. This identification may rely on the Golden's relatively long tail and patterns of white or gray on the wings and tail. At close range, the paler head and golden nape-shawl of the Golden are distinctive from other Aquila. Most other Aquila eagles are darker looking in plumage, although the slightly smaller Tawny Eagle (A. rapax) is paler than the Golden Eagle. The Eastern Imperial (A. heliaca) and Spanish Imperial Eagle (A. adalberti) are the most similar in size to the Golden Eagle among Eurasian Aquila but are distinguished by their longer neck, flatter wings in flight, white on their shoulder forewing-coverts and generally darker coloration. Verreaux's Eagle (A. verreauxii) are most similar in size and body shape to the Golden but are almost entirely black (except for some whitish color on the wing primary) in plumage and are not known to co-occur with the Golden Eagle in Africa. Among the Aquila genus, only the long-winged and tailed Wedge-tailed Eagle (A. audax) exceed the Golden Eagle in average wingspan and length.
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