Description
The plumage of an adult Bald Eagle is evenly brown with a white head and tail. The tail is moderately long and slightly wedge-shaped. Males and females are identical in plumage coloration, but sexual dimorphism is evident in the species in that females are 25 percent larger than males. The beak, feet and irides are bright yellow. The legs are feather-free, and the toes are short and powerful with large talons. The highly developed talon of the hind toe is used to pierce the vital areas of prey while it is held immobile by the front toes. The beak is large and hooked, with a yellow cere.
The plumage of the immature is brown, speckled with white until the fifth (rarely fourth, very rarely third) year, when it reaches sexual maturity. Immature Bald Eagles are distinguishable from the Golden Eagle in that the former has a more protruding head with a larger beak, straighter edged wings which are held flat (not slightly raised) and with a stiffer wing beat, and feathers which do not completely cover the legs.
The Bald Eagle has sometimes been considered the largest true raptor (accipitrid) in North America; the larger California Condor is a New World vulture. However, the Golden Eagle, in its American race, broadly overlaps in body weight and overall size with the Bald Eagle. Additionally, the Bald Eagle's close cousins, the longer-winged but shorter-tailed White-tailed Eagle and the overall larger Steller's Sea Eagle, may rarely vagrate to coastal Alaska from Asia.
The Bald Eagle has a body length of 70–102 centimeters (28–40 in) and typical wingspan between 1.8 and 2.3 m (5.9 and 7.5 ft) and mass is usually between 3 and 6.3 kilograms (6.6 and 14 lb). Females are about 25 percent larger than males, averaging 5.8 kg (13 lb), and against the males' average weight of 4.1 kg (9.0 lb). The size of the bird varies by location and generally corresponds with Bergmann's rule, since the species increases in size further away from the Equator and the tropics. The smallest specimens are those from Florida, where mature males may weigh as little as 2.3 kg (5.1 lb) and have a wingspan of 1.68 m (5.5 ft). The largest eagles are from Alaska, where large females may weigh up to 7.5 kg (17 lb) and span 2.44 m (8.0 ft) across the wings. Among standard linear measurements, the wing chord is 51.5–69 cm (20.3–27 in), the tail is 23–37 cm (9.1–15 in) long, and the tarsus is 8 to 11 cm (3.1 to 4.3 in). The culmen reportedly ranges from 3 to 7.5 cm (1.2 to 3.0 in), while the measurement from the gape to the tip of the bill is 7–9 cm (2.8–3.5 in).
The call consists of weak chirping whistles, harsher and more shrill from young birds than adults.
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