Bald Eagle (Haliaeetus leucocephalus) - Wiki
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[Photo] Haliaeetus leucocephalus(Weißkopfseeadler), Canada, Yukon. Date August 2004. Author Andreas Trepte http://de.wikipedia.org/wiki/user:Merops
The Bald Eagle (Haliaeetus leucocephalus), also known as the American Eagle, is a bird of prey found in North America, most recognizable as the national bird of the United States.
The species was on the brink of extinction in the US late in the 20th century, but now has a stable population and is in the process of being removed from the U.S. federal government's list of endangered species.
This sea-eagle gets both its common and scientific names from the distinctive appearance of the adult's head. Bald in the English name is derived from the word piebald, and refers to the white head and tail feathers and thier contrast with the darker body. The scientific name is derived from Haliaeetus, New Latin for "sea eagle," (from the Ancient Greek haliaetos) and leucocephalus, Latinized Ancient Greek for "white head", from leukos ("white") and kephale ("head").
Description and systematics
An immature Bald Eagle has speckled brown plumage, the distinctive white head and body developing 2-3 years later, before sexual maturity. This species is distinguishable from the Golden Eagle in that the latter has feathers which extend down the legs. Also, the immature Bald Eagle has more light feathers in the upper arm area, especially around the 'armpit'.
Adult females have an average wingspan of about 7 feet (2.1 meters); adult males have a wingspan of 6 ft 6 in (2 meters). Adult females weigh approximately 12.8 lb (5.8 kg), males weigh 9 lb (4.1 kg). The smallest specimens are those from Florida, where an adult male may barely exceed 5 lb (2.3 kg) and a wingspan of 6 feet (1.8 meters). The largest are the Alaskan birds, where large females may exceed 15.5 lb (7 kg) and have a wingspan of approximately 8 feet (2.4 meters).
The northern birds are the subspecies washingtoniensis, whereas the southern ones belong to the nominate subspecies leucocephalus. They are separated approximately at latitude 38° N, or roughly the latitude of San Francisco; northern birds reach a bit further south on the Atlantic Coast, where they occur south to the Cape Hatteras area. Audubon's type specimen of "Washington's Eagle" - named in honor of George Washington - was apparently an exceptionally large bird, such as are more often found in Alaska; these have been proposed as subspecies alascanus or alascensis, but the variation is clinal and follows Bergmann's Rule.
The Bald Eagle forms a species pair with the Eurasian White-tailed Eagle. These diverged from other Sea Eagles at the beginning of the Early Miocene (c. 10 mya) at latest, possibly - if the most ancient fossil record is correctly assigned to this genus - as early as the Early/Middle Oligocene, some 28 mya (Wink et al. 1996). As in other sea-eagle species pairs, this one consists of a white-headed (the Bald Eagle) and a tan-headed species. They probably diverged in the North Pacific, spreading westwards into Eurasia and eastwards into North America. Like the third northern species, Steller's Sea-eagle, they have yellow talons, beaks and eyes in adults.
Bald Eagles are powerful fliers, and also soar on thermal convection currents.
In the wild, Bald Eagles can live about 20-30 years, and have a maximum life span of approximately 50 years. They generally live longer in captivity; up to 60 years old.
Bald Eagles normally squeak and have a shrill cry, punctuated by grunts. They do not make the "eagle scream" as often shown on the television. What many recognize as the call of this species is actually the call of a Red-tailed Hawk dubbed into the film.
Range, habitat, and restoration
The Bald Eagle's natural range covers most of North America, including most of Canada, all of the continental United States, and northern Mexico. The bird itself is able to live in most of North America's varied habitats from the bayous of Louisiana to the Sonoran desert and the eastern deciduous forests of Quebec and New England. It can be a migratory bird but it also is not unheard of for a nesting pair to overwinter in its breeding area.
Once a common sight in much of the continent, the Bald Eagle was severely affected by the use of the pesticide DDT in the mid-twentieth century. While the pesticide itself was not lethal to the bird, it made an eagle either sterile or unable to lay healthy eggs: the eagle would ingest the chemical through its food and then lay eggs that were too brittle to withstand the weight of a brooding adult. By the 1960s there were fewer than 500 nesting pairs in the 48 contiguous states of the USA.
Currently it is still slowly but steadily recovering its numbers; Organizations like the Fraternal Order of Eagles which carry the Eagle as their emblem, have helped the American Bald Eagle on its recovery, by supporting other groups that rescue and preserve the Eagles and their habitat. The Bald Eagle can be found in growing concentrations throughout the United States and Canada, particularly near large bodies of water. The U.S. state with the largest resident population is Alaska; out of the estimated 70,000 Bald Eagles on Earth, half live there.
Permits are required to keep this species in captivity (e-CFR 1974). As a rule, the Bald Eagle is a poor choice for public shows, being timid, prone to becoming highly stressed, and unpredictable in nature. As remarked above, they can be long-lived in captivity if key demands are met, but do not breed well even under the best conditions. The only Bald Eagle to be born outside North America hatched on May 3, 2006 in Magdeburg Zoo, Germany.
This species has occurred as a vagrant once in Ireland. The exhausted specimen was discovered by a national parks worker in a northern heath. Presumably, a storm blew it out to sea, and the bird struggled across the Atlantic Ocean.
Bald Eagles build huge nests out of branches, usually in large trees near water. The nest may stretch as large as eight feet across and weigh up to a ton (907kg). When breeding where there are no trees, the Bald Eagle will nest on the ground.
Eagles that are old enough to breed often return to the area where they were born. An adult looking for a site is likely to select a spot that contains other breeding Bald Eagles.
Bald Eagles are sexually mature at 4 or 5 years old. Eagles produce between one and three eggs per year, but it is rare for all three chicks to successfully fly. Both the male and female take turns sitting on the eggs. The other parent will hunt for food or look for nest material.
The Bald Eagle's diet is varied, including carrion, fish, smaller birds, rodents, and sometimes food scavenged or stolen from campsites and picnics. Most prey is quite a bit smaller than the eagle, but rare predatory attacks on large birds such as the Snow Goose, the Great Blue Heron or even swans have been recorded. Also, fairly large salmon and trout have been taken as well.
To hunt fish, easily their most important live prey, the eagle swoops down over the water and snatches the fish out of the water with its talons. They eat by holding the fish in one claw and tearing the flesh with the other. Eagles have structures on their toes called spiricules that allow them to grasp fish. Osprey also have this adaptation. Bald Eagles have powerful talons. In one case, an eagle was able to fly off with the 6.8 kg (15 lb) carcass of a Mule Deer fawn.
Sometimes, if the fish is too heavy to lift, the eagle will be dragged into the water. It may swim to safety, but some eagles drown or succumb to hypothermia. Occasionally, Bald Eagles will pirate fish away from Ospreys and usually the smaller raptors will have to give up their prey, a practice known as kleptoparasitism.
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