The bald eagle (Haliaeetus leucocephalus, from Greek ἅλς, has “sea”, αἰετός aietos “eagle”, λευκός, leukos “white”, κεφαλή, kephalē “head”) is a bird of prey found in North America. A sea eagle, it has two known sub-species and forms a species pair with the white-tailed eagle (Haliaeetus albicilla). 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 which subsists mainly on fish, 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 4 m (13 ft) deep, 2.5 m (8.2 ft) wide, and 1 metric ton (1.1 short tons) in weight.Sexual maturity is attained at the age of four to five years.
Bald eagles are not actually bald; 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 percent larger than males. The beak is large and hooked. The plumage of the immature is brown.
The bald eagle is both the national bird and national animal of the United States of America. The bald eagle appears on its seal. In the late 20th century it was on the brink of extirpation in the contiguous United States. Populations have since recovered and the species was removed from the U.S. government’s list of endangered species on July 12, 1995 and transferred to the list of threatened species. It was removed from the List of Endangered and Threatened Wildlife in the Lower 48 States on June 28, 2007.
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 irides are bright yellows. 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 closely related African fish eagle (H. vocifer) (from far outside the bald eagle’s range) also has a brown body, white head, and tail, but differs from the bald 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 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.Another distinguishing feature of the immature bald eagle over the mature bird is its black, yellow-tipped beak; the mature eagle has a fully yellow beak.
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 which today is not generally considered a taxonomically of true accipitrids.However, the golden eagle, averaging 4.18 kg (9.2 lb) and 63 cm (25 in) in wing chord length in its American race (A. c. Canadensis), is merely 455 g (1.003 lb) lighter in mean body mass and exceeds the bald eagle in mean wing chord length by around 3 cm (1.2 in).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 (H. pelagicus), may, rarely, wander to coastal Alaska from Asia.
The bald eagle is a powerful flier and soars on thermal convection currents. It reaches speeds of 56–70 km/h (35–43 mph) when gliding and flapping, and about 48 km/h (30 mph) while carrying fish Its dive speed is between 120–160 km/h (75–99 mph), though it seldom dives vertically.Regarding their flying abilities, the bald eagle is considered surprisingly maneuverable in flight, bounty hunters shooting from helicopters opined that they were far more difficult to hunt while flying than golden eagles as they would turn, double back or dive as soon as approached. Bald eagles have also been recorded catching up to and then swooping under geese in flight, turning over and thrusting their talons into the other bird’s breast.It is partially migratory, depending on location. If its territory has access to open water, it remains there year-round, but if the body of water freezes during the winter, making it impossible to obtain food, it migrates to the south or to the coast. A number of populations are subject to post-breeding dispersal, mainly in juveniles; Florida eagles, for example, will disperse northwards in the summer. The bald eagle selects migration routes which take advantage of thermals, updrafts, and food resources. During migration, it may ascend in a thermal and then glide down or may ascend in updrafts created by the wind against a cliff or other terrain. Migration generally takes place during the daytime, usually between the local hours of 8:00 a.m. and 6:00 p.m., when thermals are produced by the sun.
Relationship with humans
Population decline and recovery
Once a common sight in much of the continent, the bald eagle was severely affected in the mid-20th century by a variety of factors, among them the thinning of egg shells attributed to the use of the pesticide DDT.Bald eagles, like many birds of prey, were especially affected by DDT due to biomagnification. DDT itself was not lethal to the adult bird, but it interfered with the bird’s calcium metabolism, making the bird either sterile or unable to lay healthy eggs. Female eagles laid eggs that were too brittle to withstand the weight of a brooding adult, making it nearly impossible for the eggs to hatch. It is estimated that in the early 18th century, the bald eagle population was 300,000–500,000, but by the 1950s there were only 412 nesting pairs in the 48 contiguous states of the US. Other factors in bald eagle population reductions were a widespread loss of suitable habitat, as well as both legal and illegal shooting. In 1930 a New York City ornithologist wrote that in the state of Alaska in the previous 12 years approximately 70,000 bald eagles had been shot. Many of the hunters killed the bald eagles under the long-held beliefs that bald eagles grabbed young lambs and even children with their talons, yet the birds were innocent of most of these alleged acts of predation (lamb predation is rare, human predation is thought to be non-existent).A later illegal shooting was described as “the leading cause of direct mortality in both adult and immature bald eagles,” according to a 1978 report in the Endangered Species Technical Bulletin. In 1984, the National Wildlife Federation listed hunting, power-line electrocution, and collisions in flight as the leading causes of eagle deaths. Bald eagles have also been killed by oil, lead, and mercury pollution, and by human and predator intrusion at nests.