Bald Eagle

Haliaeetus leucocephalus

Description

The bald eagle is a large, majestic bird of prey, with a barrel-shaped body between 32-40 in (80-100 cm) long, and a wingspan that reaches 7.5 ft (2.3 m). Adult birds are dark brown to black with a white head and tail. The massive, hooked bill and legs are yellow. Immature birds, which are dark brown with mottled white wings, are often mistaken for golden eagles. Immatures gradually acquire the distinctive white head and tail in their fourth year. The ongoing success of recovery efforts led the U.S. Fish and Wildlife Service (FWS) to reclassify this national symbol from Endangered to the less critical category of Threatened on July 12, 1995.

Behavior

The bald eagle feeds primarily on fish but will also eat rodents, other small mammals, and carrion. The bald eagle circles when hunting, scanning the ground with its sharp eyesight and swooping suddenly to take its prey. Adopted as the national bird in 1782 because of its fierce, independent demeanor, the bald eagle is actually rather timid.

Bald eagles are thought to mate for life. They display a spectacular courtship ritual that includes high speed dives and descending somersaults; mating birds often lock talons in mid-air. After pairing, the birds construct a nest in the fork of a tall tree or on a cliff side, often as high as 70 ft (21 m) off the ground. The nest is a massive structure of sticks, branches, and foliage, and is lined with a deep layer of finer materials. Used and added to year after year, nests can grow to enormous sizes. One 19th-century nest in Ohio measured 12 ft (3.7 m) deep and 9 ft (2.7 m) in diameter.

Females lay a clutch of two eggs as early as October in southern breeding areas and as late as mid-March in the north. Both parents incubate the eggs for about 35 days and share feeding duties for about three months until the chicks can fly and hunt on their own. The adult eagles then drive fledglings from the nest.

Most bald eagles in Canada and the northern United States move south in the fall. As a result, thousands are present in the lower 48 states from November through March. The National Wildlife Federation (NWF), which conducts an annual count, reported in 1988 that there were 11,241 wintering bald eagles throughout the country, mostly in the West and Midwest. At night groups of these wintering birds gather in communal tree roosts, which, like nests, are used in successive years.

Habitat

Bald eagle habitat varies greatly throughout its range. Generally, nesting eagles are associated with mature, secluded forests (particularly conifers) where there are flowing streams, areas of open water, and abundant fish. Eagle nests have been found in various mature trees, such as ponderosa and loblolly pines, cottonwoods, oaks, poplars, and beech.

Distribution

Records show that bald eagles once nested in most of North America—in Canada, Alaska, and at least 45 of the lower 48 states. In some states, decline in the numbers of nesting bald eagles was already well under way in the 19th century. In other states, significant decline probably did not occur until the 1940s.

When the FWS downlisted the bald eagle from Endangered to Threatened in 1995, the action marked a dramatic turnaround for the eagle, which was down to as few as 417 nesting pairs in the lower 48 states in the 1960s. Since that time, the number of nesting pairs has climbed to nearly 4,500 and is still increasing. Since the late 1970s, bald eagle numbers have been doubling every 6-7 years. By 1993, bald eagle numbers in the lower 48 states had climbed from about 417 nesting pairs in 1963 to more than 4,000 pairs of adult birds. Surveys indicate the population has risen 10% between 1993 and 1999.

Alaska is home for the largest population of bald eagles in North America, an estimated 30,000 individuals by 1990. Another large population, claimed by some researchers to approach the Alaskan population in size, breeds in Canada's western provinces. These populations are considered stable and healthy. In the lower 48 states, 2,440 breeding pairs nested in 1988, according to the FWS. The greatest concentrations are found in the Pacific Northwest, the upper Great Lakes, Florida, and around the Chesapeake Bay.

Of the 696 breeding pairs in the Pacific Northwest in the late 1980s, the largest number is found in Washington (305 pairs). There, bald eagles nest on the San Juan Islands and the Olympic Peninsula coastline. In Oregon 150 pairs nest in the Klamath Basin, near lakes in the high Cascades, and along the coastline and the lower Columbia River.

In the northern and Great Plains states (New England west to Colorado and Utah) 1,011 pairs nested in 1988, principally in Minnesota, Wisconsin, and Michigan. By 1992, there were 149 pairs wintering in New England. Maine, with the region's largest nesting population, also supported the most wintering birds, estimated at about 400. Massachusetts reported a record high of 70 wintering birds in 1992-1993, while Connecticut reported 61, New Hampshire 23, and Vermont 12. In Rhode Island, where a sighting of a bald eagle is still an uncommon event, eagles were observed from November to March, and three were counted during the mid-winter census.

In the southwest, most of Arizona's eagles are concentrated along the Salt, Verde, and Gila Rivers just east of the large Phoenix metropolitan area. In 1994, 27 (81%) of Arizona territories were occupied, but only 12 (36%) were successful, fledging a total of 18 young. This performance of 0.66 fledglings per occupied territory is below the 0.81 average over the preceding 20 years. The two territories in New Mexicowere both successful in 1994, fledging a total of three young. Other concentrations of eagles include Florida where 399 were documented in the late 1980s, and around the Chesapeake Bay, where 181 pairs nested in Maryland, Delaware, and Virginia.

Threats

Historically, the most important threat to the bald eagle has been habitat loss, including both the destruction of wetlands, and the cutting of the tall trees that eagles need as a platform on which to build their bulky nests. In some areas the bald eagle was shot because it was wrongly perceived to be a threat to chickens, livestock, and wild ducks. Since about the 1950s, bald eagles have also been poisoned by the insidious influences of persistent organochlorine chemicals, such as the insecticides DDT and dieldrin, the industrial chemicals PCBs, and trace contaminants such as dioxins and furans. Bald eagles became exposed to these bioaccumulating chemicals through their food web (the eagles are top predators in their ecosystem). In some regions eagles have suffered from mercury poisoning, also ingested from their food of fish and other small animals. Many eagles have also been poisoned by lead, after eating lead bullets and shot from scavenged carrion. These various effects have resulted in a large decrease in the population of bald eagles in most of North America, but particularly in the lower-48 states and parts of southern Canada. Since the mid-1980s, however, the species has had somewhat of an increase in populations, largely due to the banning of the use of most organochlorine insecticides and PCBs in North America during the 1970s.

Conservation and Recovery

In the 1940s, after a long and steady decline in bald eagle numbers caused by shooting, alteration of habitat, and human encroachment into the wilderness, the pesticide DDT was introduced into the environment. Pesticide residues worked their way up the food chain and accumulated in the tissues of larger predators. Some birds, including the peregrine falcon and the bald eagle, began laying eggs with abnormally thin shells. These eggs were unable to bear the weight of the incubating adult birds and broke. The bald eagle suffered an abrupt population crash and disappeared from many states. By 1981, occupied nests were known in only 30 states, and about 90% of nesting pairs were concentrated in just ten states.

Between 1960 and 1973 nesting bald eagles disappeared from 18 of 44 Michigan counties. The Chesapeake Bay population fell from 150 pairs in 1962 to about 85 pairs in 1970. Nesting pairs disappeared from the upper portions of rivers and were greatly reduced at the upper end of the bay. Bald eagles were once common nesters along the Atlantic coast from the Chesapeake Bay to the Florida Keys, but by the late 1970s the Florida population alone was secure, and that had been reduced by half.

When DDT was banned in the United States in the early 1970s, the eagle's reproduction at once began to improve. Recovery was assisted by intensive efforts by federal agencies that included systematic monitoring, enhanced protection, captive breeding, relocation of wild birds, and a far-flung publicity program. State agencies became increasingly involved through tax-funded programs to monitor eagle nests and assist reintroduction projects. The Nature Conservancy and the NWF acquired important nesting sites and wintering habitat, and actively pursued conservation agreements with landowners. The combined efforts paid off.

By 1980 and 1981 the nesting population in the lower 48 states had doubled. The rebound has continued so strongly that the FWS is currently in the process of reclassifying part or all of the bald eagle populations in the lower 48 states from Endangered to Threatened. In recent years, the relocation of wild chicks has been widely used to help the bald eagle recolonize its former range. Chicks are taken from nests in Alaska or Canada and released in states with few nesting eagles. Relocation has succeeded in many states, including Pennsylvania, New York, and Indiana, and has enabled the FWS to end its bald eagle captive breeding program.

The final rule for the 1995 reclassification of the bald eagle from Endangered to Threatened final rule goes further than the June 30, 1994, reclassification proposal, which would have retained the bird's endangered status in Arizona, New Mexico, western Texas, and part of southeastern California. A thorough review of scientific data revealed that the eagle could be reclassified in those areas as well.

In addition to efforts such as the ban on DDT use, the Endangered Species Act (ESA) promoted bald eagle recovery by curbing habitat destruction and protecting nesting sites. Some areas of particular importance were added to the National Wildlife Refuge System. Other recovery actions included the release of healthy young eagles in habitat where natural reproduction no longer occurred and the rehabilitation of injured birds. Although the bald eagle seems well on the way to recovery, it still faces a number of threats. Illegal shooting is the most frequently recorded cause of eagle mortality, although the rate of shooting deaths has declined in recent years. The NWF offers a $500 reward for information leading to the conviction of persons shooting eagles. Some birds continue to die from lead poisoning contracted by feeding on pellet-killed carrion.

Collision with power lines and electrocution are other causes of bald eagle mortality. To counter these, power companies, particularly in the Northwest, have begun extensive design changes aimed at reducing eagle deaths. In recent years, privately sponsored rehabilitation facilities have been established to treat injured eagles and return them to the wild. In addition to population increases, the return of bald eagles to abandoned breeding grounds gives conservationists reason to cheer.

In 1987, a bald eagle nest in Tennessee produced young for the first time since breeding eagles disappeared from the state decades ago; in 1989 there were 11 active nests in Tennessee. And that same year saw the first recorded instance of bald eagles nesting in Kansas.

The recovery of the bald eagle has not occurred without controversy, however. In December 1988 the General Accounting Office issued a study that was sharply critical of the management of the federal Endangered Species Program. The study concluded that the FWS and the Interior Department concentrated an undue amount of resources into the recovery of several high-profile species, such as the bald eagle and the black-footed ferret, while ignoring many species of plants and animals that have less public appeal but are more immediately in danger of extinction.

The highly publicized recovery of the bald eagle was an effort, concluded the report, to indulge public tastes at the expense of scientific priorities.

Since the late 1970s, bald eagle numbers have been doubling every six to seven years. Surveys indicate the population has risen 10% between 1993 and 1999. Due to continuing threats, however, the species is not yet ready for complete de-listing. Episodes of poisoning still occur periodically, and the cumulative effects of incremental habitat loss are a problem in some areas. As a Threatened species, the bald eagle will remain under ESA protection.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1 Federal Drive
BHW Federal Building
Fort Snelling, Minnesota 55111
Telephone: (612) 713-5360
http://midwest.fws.gov/

References

Dunstan, T. C. 1978. "Our Bald Eagle: Freedom's Symbol Survives." National Geographic 153(2):186-199.

Fischer, D. L. 1985. "Piracy Behavior of Wintering Bald Eagles." Condor 87:245-251.

General Accounting Office. 1988. "Endangered Species: Management Improvements Could Enhance Recovery Program." GAO/RCED-89-5. General Accounting Office, Washington, D.C.

Green, N. 1985. "The Bald Eagle." In R. L. Di Silvestro, ed., Audubon Wildlife Report 1985. National Audubon Society, New York.

Bald eagle

The bald eagle (Haliaeetus leucocephalus ), one of North America's largest birds of prey with a wingspan of up to 7.5 ft (2.3 m), is a member of the family Accipitridae. Adult bald eagles are dark brown to black with a white head and tail; immature birds are dark brown with mottled white wings and are often mistaken for golden eagles (Aquila chrysaetos ). Bald eagles feed primarily on fish, but also eat rodents, other small mammals and carrion. The bald eagle is the national emblem for the United States, adopted as such in 1782 because of its fierce, independent appearance. This characterization is unfounded, however, as this species is usually rather timid.

Formerly occurring over most of North America, the bald eagle's range—particularly in the lower 48 states—had been drastically reduced by a variety of reasons. One being its exposure to DDT and related pesticides, which are magnified in the food chain/web . This led to reproductive problems, in particular, thin-shelled eggs that were crushed during incubation. The banning of DDT use in the United States in 1972 may have been a turning point in the recovery of the bald eagle. Eagle populations also were depleted due to lead poisoning . Estimates are that for every bird that hunters shot and carried out with them, they left behind about a half pound of lead shot , which affects the wildlife in that ecosystem long after the hunters are gone. Since 1980, more than 60 bald eagles have died from lead poisoning. Other threats facing their populations include habitat loss or destruction, human encroachment, collisions with high power lines, and shooting.

In 1982 the population in the lower 48 states had fallen to less than 1,500 pairs, but by 1988 their numbers had risen to about 2,400 pairs. Due to strict conservation laws, the numbers have continued to rise and there are now 6,000 pairs. On July 4, 2000, the bald eagle was removed from the Endangered listing and is now listed as Threatened in the lower 48 states. The bald eagle is not endangered in the state of Alaska, since a large, healthy population of about 35,000 birds exists there. During the annual salmon run, up to 4,000 bald eagles congregate along the Chilkat River in Alaska to feed on dead and dying salmon.

Bald eagles, which typically mate for life and build huge platform nests in tall trees or cliff ledges, have been aided by several recovery programs, including the construction of artificial nesting platforms. They will reuse , add to, or repair the same nest annually, and some pairs have been known to use the same nest for over 35 years. Because the bald eagle is listed as either endangered or threatened throughout most of the United States, the federal government provides some funding for its conservation and recovery projects. In 1989, the federal government spent $44 million on the conservation of threatened and endangered species . Of the 554 species listed, $22 million, half of the total allotment, was spent on the top 12 species on a prioritized list. The bald eagle was at the top of that list and received $3 million of those funds.

[Eugene C. Beckham ]

RESOURCES

BOOKS

Ehrlich, P., D. Dobkin, and D. Wheye. Birds in Jeopardy. Stanford, CA: Stanford University Press, 1992.

Temple, S., ed. Endangered Birds: Management Techniques for Preserving Threatened Species. Madison: University of Wisconsin Press, 1977.

PERIODICALS

Dunstan, T. C. "Our Bald Eagle: Freedom's Symbol Survives." National Geographic 153 (1978): 186–99.

ORGANIZATIONS

American Eagle Foundation, P.O. Box 333, Pigeon Forge, TN USA 37868 (865) 429-0157, Fax: (865) 429-4743, Toll Free: (800) 2EAGLES, Email: [email protected]., <http://www.eagles.org>

bald eagle Large bird of prey that lives in North America, where it feeds on fish and small mammals. It is brown with a white head and tail and a yellow bill. Its tail feathers were used in the headdresses of some Native Americans. It is the national emblem of the USA. Though now protected by law, it remains an endangered species. Species Haliaeetus leucocephalus.

bald ea·gle • n. a white-headed North American eagle (Haliaeetus leucocephalus) that includes fish among its prey. Now most common in Alaska, it is the national emblem of the US.