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bald eagle
Haliaeetus leucocephalus

STATUS

U.S.A. Threatened and California Endangered; proposed for U.S.A. delisting

LIFE HISTORY

The bald eagle is a majestic raptor that was adopted as the United States' national emblem in 1782. The white head and tail and the large dark brown body and wings are the features that distinguish adult bald eagles from other raptors. The adults also have yellow eyes, cere (base of beak, including nostrils), bill, legs, and feet with black claws. However, it is not until the birds are 4 or 5 years old that they fully attain this distinctive plumage. There are at least five different plumages that apparently correspond with age; Juvenile, Basic I, Basic II, Basic III, and Adult; however, the literature varies in regards to the ages associated with these plumages. As seen in flight, the head and tail of an adult bald eagle project from the body at equal lengths; while on a non-adult, the head projects more than one-half the length of the tail. When seen from head on, the extended wings of this species are held level with the body.

Non-adult plumage is similar to that of the golden eagle (Aquila chrysaetos), primarily dark brown with variable amounts of white mottling. However, on the undersides of the wing, non-adult bald eagles have white patches where the wings meet the body (often referred to as wing pits, or axillars) with white diagonal lines extending outward from there. White mottling occurs on their upperparts as well, all to varying degrees. Their tails vary from darkish- to dirty-white, with dark edges and tips.

Bald eagles are usually associated with a source of permanent water, such as reservoirs, lakes, and free-flowing rivers, with abundant fish and nearby sites for perching, roosting, and, in season, nesting. These sites include snags or other open perches, such as broken-topped trees and rocks near the water. Their primary prey is fish, especially salmon, but they will also eat small mammals, various water birds, such as waterfowl, and carrion. In the winter, provided the roosting sites and food are abundant, the eagles will roost in groups, particularly in conifer stands or along rivers with migrating salmon. During salmon runs in Alaska, up to 4,000 eagles have been known to congregate along the Chiklat River.

The bald eagle searches for prey from a soaring flight or from a perch, then swoops down and grabs its prey. These eagles are known to wade in shallow water to pursue fish with their bill or talons. Bald eagles tend to cooperatively hunt, particularly when pursuing lagomorphs, such as cottontails and black-tailed hares; they will try and flush them out by using short flights back and forth across the vegetation, or by watching from a perch and waiting for the prey to appear. Occasionally, bald eagles visit flooded fields, pouncing on the small mammals displaced by the water. Piracy of prey from other species is a common foraging tactic of immature bald eagles.

The breeding season for bald eagles begins in February and lasts through July, with pairs establishing long-term bonds. They breed in open areas along coasts, rivers, and large lakes, usually away from human disturbances. In California, a study showed that approximately 87% of their nest sites were within 1 mile (1.6 km) of water.

Platform nests of sticks are lined with vegetation and other fine materials and are built in large snags and old growth trees with open branches. The nests are often built in the fork of the tree and range from 3 to 61 meters (10-200 ft) above the ground. Cliff nests vary in size from those with very little nesting materials to those that are massive structures. Some eagles have been known to use the same nest for more than 35 years; occasionally, they may use more than one nest in a season.

A clutch of one to three eggs, usually two, is laid annually. The incubation period lasts between 34 and 36 days with both parents participating. The eggs hatch asynchronously (at different times, usually with an interval of a day or two in between). The young fledge when they are 70 to 98 days of age. The bald eagle first breeds at 4 or 5 years of age.

Populations of bald eagles outside of Alaska have declined because of habitat loss and reproductive failure due to pesticides and heavy metals in their diets. Restrictions placed on certain pesticides have allowed for the comeback of this species in some of its historic range. Industrial development, logging, recreational development, and other human disturbances have caused eagles to abandon nests and remain potential threats to this species.

Distribution

Bald eagles' breeding range extends from the Alaskan coast down through western Canada (with the exception of southern regions of Alberta and Saskatchewan), eastward through southern Canada and the Great Lakes, then northward to the eastern Canadian coast. Eagles reside (breed and winter) along their coastal habitat in the eastern states, throughout most of Florida, and along the Gulf Coast. In the west, they reside along the western coast from southern Alaska through the Pacific Northwest to Northern California. A few small populations live in Arizona and Colorado.

In the winter, bald eagles can be found throughout most of the United States west of the Mississippi River. During this time, high concentrations of eagles are found along the coast from southern Alaska and western Canada to Washington and along the upper Mississippi River.

Within California, bald eagles are permanent residents in the north and uncommon winter migrants, particularly in the south. Northern California has a large breeding population and approximately half of the winter population is found in the Klamath Basin along the Oregon border. In southern California, the largest concentrations occur near inland waters, including Big Bear Lake, Cachuma Lake, Lake Mathews, Nacimiento Reservoir, San Antonio Reservoir, and along the Colorado River.

In central California, bald eagles nest at Millerton Lake State Recreation Area (formed by Friant Dam, Fresno/Madera counties). In the winter, bald eagles can be found at this lake, along the San Joaquin River downstream of the dam, and along the Tuluomne and Stanislaus rivers, especially near their reservoirs located in the foothills of the Sierra Nevada.

CLASSIFICATION

Order FALCONIFORMES, Family ACCIPTRIDAE, Genus Haliaeetus, Species leucocephalus

SUBSPECIES

According to Johnsgard (1990), there are two subspecies: H. l. leucocephalus, which breeds in the southern United States and Baja California; and H. l. alascanus which breeds from the Bering Island across northern North America. The two subspecies intergrade with one another in the central and northern states.

RECENT SYNONYMS

None.

OTHER COMMON NAMES

American eagle.

REFERENCES

Wheeler, B. K., and W. S. Clark. 1995. A photographic guide to North American raptors. Academic Press, San Diego, CA, 198 pp; Johnsgard, P. A. 1990. Hawk, eagles, and falcons of North America: biology and natural history. Smithsonian Institution Press, Washington, DC, 403 pp; State of California, Dept. Fish and Game. 1990. California's Wildlife, Vol. II: Birds (D.C. Zeiner, W.F. Laudenslayer, Jr., K. Mayer and 1M. White, eds.). The Resources Agency, Sacramento, 407 pp; Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. The birder's handbook: a field guide to the natural history of North American Birds. Simon and Schuster, Inc., NY, 785 pp; Clark, W. S., and B. K. Wheeler. 1987. A field guide to hawks: North America. The Peterson field guide series, Houghton Mifflin Co., Boston, MA, 198 pp.

SIZE

Length:
70-90 cm (27-35 inches)
Wingspread:
180-225 cm (71-89 inches)
Weight:
2.0-6.2 kg (4.4-13.6 pounds)

IDENTIFICATION

When seen from head on, the extended wings of a bald eagle are level, in contrast to the golden eagle whose wings are held in a slight dihedral (uplifted angle). The beak and cere of an adult bald eagle are usually the same color (yellow), whereas those of the golden eagle are tri-colored: cere yellow, base of beak grayish, and tip black. On flying golden eagles, the head projects from the body less than one-half the length of the tail.

AUTHOR OF PROFILE

N. L. Brown

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