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 which subsists mainly on fish, which it swoops down upon 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 13 ft deep, 8.2 ft wide, and 1.1 short tons in weight. Sexual maturity is attained at the age of four to five years.
Bald eagles are not 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 yellow beak is large and hooked. The plumage of the immature is brown.
The bald eagle is the national bird of the United States of America and 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's 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 Ancient Greek: ἁλιάετος, romanized: haliaetos, lit. 'sea eagle'), and the specific name, leucocephalus, is Latinized (Ancient Greek: λευκός, romanized: leukos, lit. 'white') and (κεφαλή, kephalḗ, 'head').
Bald eagle anatomy
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.
There are two recognized subspecies of bald eagle:
- 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.
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.
The largest eagles are from Alaska, where large females may weigh more than 15 lb and span 8 ft 0 in across the wings. A survey of adult weights in Alaska showed that females there weighed on average 11.8 lb, respectively, and males weighed 9.3 lb against immatures which averaged 11.2 lb and 8.9 lb in the two sexes. An Alaskan adult female eagle that was considered outsized weighed some 16 lb. 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 18 lb. Among standard linear measurements, the wing chord is 20.3–27.2 in, the tail is 9.1–14.6 in long, and the tarsus is 3.1 to 4.3 in. The culmen reportedly ranges from 1.2 to 3.0 in, while the measurement from the gape to the tip of the bill is 2.8–3.5 in. 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 2.69 in and 1.62 in.
Diet and feeding
The bald eagle is an opportunistic carnivore with the capacity to consume a great variety of prey. Fish often comprise most of the eagle's diet throughout their range. In 20 food habit studies across the species' range, fish comprised 56% of the diet of nesting eagles, birds 28%, mammals 14% and other prey 2%. More than 400 species are known to be included in the bald eagle's prey spectrum, far more than its ecological equivalent in the Old World, the white-tailed eagle, is known to take. Despite its considerably lower population, the bald eagle may come in second amongst all North American accipitrids, slightly behind only the red-tailed hawk, in number of prey species recorded.
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