The bald eagle (Haliaeetus leucocephalus) is a bird of prey found in North America. A sea eagle, it has two known subspecies and forms a species pair with the white-tailed eagle (Haliaeetus albicilla), which occupies the same niche as the bald eagle in the Palearctic. Its range includes most of Canada and Alaska, all of the contiguous United States, and northern Mexico. It is found near large bodies of open water with an abundant food supply and old-growth trees for nesting.
The bald eagle is an opportunistic feeder that subsists mainly on fish, upon which it swoops down and snatches from the water with its talons. It builds the largest nest of any North American bird and the largest tree nests ever recorded for any animal species, up to deep, wide, and in weight. Sexual maturity is attained at the age of four to five years.
Bald eagles are not bald in the literal sense; the name derives from an older meaning of the word, "white-headed". The adult is mainly brown with a white head and tail. The sexes are identical in plumage, but females are about 25% larger than males. The yellow beak is large and hooked. The plumage of the immature is brown.
The bald eagle is the national bird and national symbol of the United States and appears on its seal. In the late 20th century it was on the brink of extirpation in the contiguous United States, but measures such as banning the practice of hunting bald eagles and banning the use of the harmful pesticide DDT slowed the decline of their population. Populations have since recovered, and the species' status was upgraded from "endangered" to "threatened" in 1995 and removed from the list altogether in 2007.
Taxonomy
The bald eagle is placed in the genus Haliaeetus (sea eagles), and gets both its common and specific scientific names from the distinctive appearance of the adult's head. Bald in the English name is from an older usage meaning "having white on the face or head" rather than "hairless", referring to the white head feathers contrasting with the darker body.
The genus name is Neo-Latin: Haliaeetus (from the ), and the specific name, leucocephalus, is Latinized () and ().
The bald eagle was one of the many species originally described by Carl Linnaeus in his 18th-century work Systema Naturae, under the name Falco leucocephalus.
The bald eagle forms a species pair with the white-tailed eagle of Eurasia. This species pair consists of a white-headed and a tan-headed species of roughly equal size; the white-tailed eagle also has overall somewhat paler brown body plumage. The two species fill the same ecological niche in their respective ranges. The pair diverged from other sea eagles at the beginning of the Early Miocene (c. 10 Ma BP) at the latest, but possibly as early as the Early/Middle Oligocene, 28 Ma BP, if the most ancient fossil record is correctly assigned to this genus.
Subspecies There are two historically recognized subspecies of bald eagle, although it is believed these may be the same species with size differences according to Bergmann's Rule. H. l. leucocephalus (Linnaeus, 1766) is the nominate subspecies. It is found in the southern United States and Baja California peninsula. H. l. washingtoniensis (Audubon, 1827), synonym H. l. alascanus (Townsend, 1897), the northern subspecies, is larger than southern nominate leucocephalus. It is found in the Northern United States, Canada and Alaska.
Description
The plumage of an adult bald eagle is evenly dark 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% larger than males. The beak, feet and irises 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 adult bald eagle is unmistakable in its native range. The African fish eagle (Ichthyophaga vocifer) (from far outside the bald eagle's range) also has a brown body (albeit of somewhat more rufous hue), white head and tail, but differs from the bald eagle in having a white chest and black tip to the bill.
The plumage of the immature is a dark brown overlaid with messy white streaking until the fifth (rarely fourth, very rarely third) year, when it reaches sexual maturity. Immature bald eagles are distinguishable from the golden eagle (Aquila chrysaetos), the only other very large, non-vulturine raptorial bird in North America, in that the former has a larger, 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. When seen well, the golden eagle is distinctive in plumage with a more solid warm brown color than an immature bald eagle, with a reddish-golden patch to its nape and (in immature birds) a highly contrasting set of white squares on the wing.
The bald eagle has sometimes been considered the largest true raptor (accipitrid) in North America. The only larger species of raptor-like bird is the California condor (Gymnogyps californianus), a New World vulture that today is not generally considered a taxonomic ally of true accipitrids. However, the golden eagle, averaging and in wing chord length in its American race (Aquila chrysaetos canadensis), is merely lighter in mean body mass and exceeds the bald eagle in mean wing chord length by around . Additionally, the bald eagle's close cousins, the relatively longer-winged but shorter-tailed white-tailed eagle and the overall larger Steller's sea eagle (Haliaeetus pelagicus), may, rarely, wander to coastal Alaska from Asia.
The bald eagle has a body length of . Typical wingspan is between and mass is normally between . Females are about 25% larger than males, averaging as much as , and against the males' average weight of .
The size of the bird varies by location and generally corresponds with Bergmann's rule: the species increases in size further away from the equator and the tropics. For example, eagles from South Carolina average in mass and in wingspan, smaller than their northern counterparts. One field guide in Florida listed similarly small sizes for bald eagles there, at about . Of intermediate size, 117 migrant bald eagles in Glacier National Park were found to average but this was mostly (possibly post-dispersal) juvenile eagles, with six adults here averaging . Wintering eagles in Arizona (winter weights are usually the highest of the year since, like many raptors, they spend the highest percentage of time foraging during winter) were found to average .
The largest eagles are from Alaska, where large females may weigh more than and span across the wings. A survey of adult weights in Alaska showed that females there weighed on average , respectively, and males weighed against immatures which averaged and in the two sexes.. An Alaskan adult female eagle that was considered outsized weighed some . R.S. Palmer listed a record from 1876 in Wyoming County, New York of an enormous adult bald eagle that was shot and reportedly scaled . Among standard linear measurements, the wing chord is , the tail is long, and the tarsus is . The culmen reportedly ranges from , while the measurement from the gape to the tip of the bill is . The bill size is unusually variable: Alaskan eagles can have up to twice the bill length of birds from the Southern United States (Georgia, Louisiana, Florida), with means including both sexes of and in culmen length, respectively, from these two areas.
The call consists of weak staccato, chirping whistles, kleek kik ik ik ik, somewhat similar in cadence to a gull's call. The calls of young birds tend to be harsher and shriller than those of adults.
Range
The bald eagle's natural range covers most of North America, including most of Canada, all of the continental United States, and northern Mexico. It is the only sea eagle endemic to North America. Occupying varied habitats from the bayous of Louisiana to the Sonoran Desert and the eastern deciduous forests of Quebec and New England, northern birds are migratory, while southern birds are resident, remaining on their breeding territory all year. At minimum population, in the 1950s, it was largely restricted to Alaska, the Aleutian Islands, northern and eastern Canada, and Florida. From 1966 to 2015 bald eagle numbers increased substantially throughout its winter and breeding ranges, and as of 2018 the species nests in every continental state and province in the United States and Canada.
The majority of bald eagles in Canada are found along the British Columbia coast while large populations are found in the forests of Alberta, Saskatchewan, Manitoba and Ontario. Bald eagles also congregate in certain locations in winter. From November until February, one to two thousand birds winter in Squamish, British Columbia, about halfway between Vancouver and Whistler. In March 2024, bald eagles were found nesting in Toronto for the first time. The birds primarily gather along the Squamish and Cheakamus Rivers, attracted by the salmon spawning in the area. Similar congregations of wintering bald eagles at open lakes and rivers, wherein fish are readily available for hunting or scavenging, are observed in the Northern United States.
It has occurred as a vagrant twice in Ireland; a juvenile was shot illegally in County Fermanagh on January 11, 1973 (misidentified at first as a white-tailed eagle), and an exhausted juvenile was captured near Castleisland in County Kerry on November 15, 1987. There is also a record of it from Llyn Coron in Anglesey, United Kingdom, from October 17, 1978; the provenance of this individual eagle has remained in dispute.
Habitat
The bald eagle occurs during its breeding season in virtually any kind of American wetland habitat such as seacoasts, rivers, large lakes or marshes or other large bodies of open water with an abundance of fish. Studies have shown a preference for bodies of water with a circumference greater than , and lakes with an area greater than are optimal for breeding bald eagles.
The bald eagle typically requires old-growth and mature stands of coniferous or hardwood trees for perching, roosting, and nesting. Tree species reportedly is less important to the eagle pair than the tree's height, composition and location. Perhaps of paramount importance for this species is an abundance of comparatively large trees surrounding the body of water. Selected trees must have good visibility, be over tall, an open structure, and proximity to prey. If nesting trees are in standing water such as in a mangrove swamp, the nest can be located fairly low, at as low as above the ground. In a more typical tree standing on dry ground, nests may be located from in height. In Chesapeake Bay, nesting trees averaged in diameter and in total height, while in Florida, the average nesting tree stands high and is in diameter. Trees used for nesting in the Greater Yellowstone area average high. Trees or forest used for nesting should have a canopy cover of no more than 60%, and no less than 20%, and be in close proximity to water. Most nests have been found within of open water. The greatest distance from open water recorded for a bald eagle nest was over , in Florida.
Bald eagle nests are often very large in order to compensate for size of the birds. The largest recorded nest was found in Florida in 1963, and was measured at wide and deep.