SPECIES

Bald Eagle Haliaeetus leucocephalus Scientific name definitions

David A. Buehler
Version: 2.0 — Published October 7, 2022

Identification

Field Identification

Total length 71–96 cm, wingspan 168–244 cm, body mass 3.0–6.3 kg (1), with largest birds in northern part of range (Alaska, Canada), and smallest in southeastern and southwestern United States. The female is about 25% larger than the male. The flight is characterized by slow, methodical, and powerful wing beats; it soars and glides on broad, wide wings that are held flat and largely at a right angle to the body; the head and neck are about half the length of the tail in flight (2).

The appearance of adults (Definitive Basic Plumage) is acquired at 4.5 years of age in about 25% of birds, and in most or all birds by 5.5 years (3, 4). Definitive Basic Plumage is unmistakable, with the largely dark brown body contrasting starkly with the white head, tail, and tail coverts, and the yellow iris, beak, cere, legs, and feet. The Juvenile Plumage is characterized by a dark brown head, body, wings, and tail, excepting limited white mottling on the underwing coverts, axillars, and posterior underparts. The beak and cere of juveniles are blackish gray, and the iris dark brown. Following a limited Preformative Molt in the first cycle, later predefinitive plumages become increasingly variable, such that aging birds becomes somewhat unreliable from the third through fifth molt cycles (i.e., 4.5–5.5 years of age). The head undergoes changes with progressive molts, from dark brown in juvenile to white in adult. Formative and Second Basic plumages (1.5–2.5 years of age) can have a dark breast contrasting with a variably paler throat and belly, an inverted whitish triangular patch on the mantle, and increased white on the underwing feathers. Birds in Third Basic and Fourth Basic plumages (3.5–4.5 years of age) may have a largely white head with brown-gray flecking extending posteriorly from the eye, giving the appearance of an eye stripe. The coloration of the body tends to be variable in the amount and distribution of white mottling on the dark-brown plumage. As individuals approach adulthood (4.5 years of age), contour feathers become more consistently dark brown, although limited white flecking can still occur, especially on the belly and breast. Tail coloration also changes gradually from mostly black-brown in juveniles to completely white in adults. The rectrices of Third Basic and Fourth Basic plumages can be largely white, with limited brown-black flecking on their proximate edges. Sexes are similar in plumage at all ages.

The beak and cere color also change progressively with age from black-gray in juveniles to yellow in adults; iris color changes from dark brown in juveniles, to buffy brown or cream-colored in individuals in Second Basic Plumage, to yellow in adults.

Similar Species

The adult Bald Eagle is the only North American raptor with and all-white head and tail. Immatures and juveniles are most easily confused with the Golden Eagle (Aquila chrysaetos). In all plumages, it can be distinguished from Golden Eagle by its more massive bill and unfeathered lower tarsi. Additionally, Golden Eagle has a golden nape (can be difficult to see in younger birds) that is not present in Bald Eagle. In flight, Bald Eagle soars with its wings held flat, whereas Golden Eagle soars with wings held slightly above horizontal. The separation of Golden Eagle from immature and juvenile Bald Eagle otherwise focuses on the underwing. Until Definitive Basic Plumage is reached, Bald Eagle has pale mottling on the underwing coverts, which are solid dark in the Golden Eagle, and Golden Eagle has white to gray at the base of the secondaries and primaries until Definitive Basic Plumage is reached. Additionally, Golden Eagle never has white on the head or body, unlike the Bald Eagle in most plumages. In Juvenile through Third Basic plumages, Bald Eagle can also be confused with vultures and large buteos at a distance (5), but the massive size and bill of the Bald Eagle are usually evident.

The White-tailed Eagle (Haliaeetus albicilla) of the Palearctic occasionally occurs in Alaska. Adults are rather easily distinguished from Bald Eagle: the head, neck and chest are dingy white with moderate brownish streaks and mottling (overall imparting a tan color), and the upperwing coverts and upper back feathers are brown with distinct dingy white edging; additionally, the tail is relatively short, and the uppertail coverts are dark. Immature and juvenile White-tailed Eagle have shorter tails and 7 (rather than 6) emarginated primaries; additionally, they never have extensive dark on the distal portion of tail as is typical of Bald Eagle (through Fourth Basic Plumage) and never have as much white on the underwing coverts as do many Bald Eagle (through Second Basic; 6). The Steller's Sea-Eagle (Haliaeetus pelagicus) is also a vagrant to North America (mostly Alaska). At all ages, Steller's Sea-Eagle can be distinguished by its larger bill and longer and more obviously wedge-shaped tail. In predefinitive plumages, it has more distinct white feathering on the lesser upperwing coverts, more white on the tail, and never has white on the head. Adult Steller's Sea-Eagle is distinctive, with a dark head, fully white lesser coverts, and white tarsal feathering.

Recommended Citation

Buehler, D. A. (2022). Bald Eagle (Haliaeetus leucocephalus), version 2.0. In Birds of the World (P. G. Rodewald and S. G. Mlodinow, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.baleag.02