Bald Eagle

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Revision as of 17:46, 7 June 2007

The Bald Eagle (Haliaeetus leucocephalus), also known in the United States 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 extirpation in the U.S. late in the twentieth 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. The Bald Eagle was officially reclassified from "Endangered" to "Threatened" on July 12, 1995 by the U.S. Fish & Wildlife Service. On July 6, 1999, there was a proposal initiated "To Remove the Bald Eagle in the Lower 48 States From the List of Endangered and Threatened Wildlife." [1] It is expected to be delisted by June 29.[2]

This sea-eagle gets both its normal 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 their 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 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'.

Body length ranges from 27 to 40 inches (68-100 cm). 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 16.5 lb (7.5 kg) and have a wingspan of over 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<ref> As explicitly stated by Audubon. However, the subspecific name he chose - washingtoniensis - means properly "from Washington (state)". There has been considerable confusion, with some authors changing it to washingtoni, "(George) Washington's", but the form as originally written is correct.</ref> - 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<ref> The authors' reservations about using the generalized "2%" rate of molecular evolution have since proven to be well-founded.</ref>). 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 typically live about 20-30 years, but can realize a life span of approximately 50 years. They generally live longer in captivity, up to 60 years.

Bald Eagles normally squeak and have a shrill cry, punctuated by grunts. They do not make the "eagle scream", usually the call of a Red-tailed Hawk, that is sometimes dubbed into films for dramatic effect.