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Back In Flight

Mar 11, 2013 10:05PM ● By Anonymous

BALD EAGLE BIOLOGY

Bald eagles live near rivers, lakes, and marshes, where they can find fish, their staple food—although they will feed on waterfowl, turtles, rabbits, snakes, and other small animals, and even carrion. Also crucial to their survival are perching areas, and nesting sites. In winter, the birds congregate near open water in tall trees for spotting prey and night roosts for shelter.

Eagles mate for life, choosing the tops of large trees to build nests, which they typically use and enlarge each year. Nests may reach 10 feet across and weigh a half ton. They may also have one or more alternate nests within their breeding territory. In treeless regions, eagles may nest in cliffs or on the ground. The birds travel great distances but usually return to breeding grounds within 100 miles of the place they were raised. Bald eagles can live 15 to 25 years in the wild, longer in captivity.

Bald eagles make their new nests an average of two feet deep and five feet across. Some nests can reach 10 feet wide and weigh as much as 4,000 pounds.

Breeding bald eagles typically lay one to three eggs once a year. The eggs hatch after about 35 days. The young eagles are flying within three months and are on their own about a month later. Young bald eagles are mostly dark brown until they are four to five years old, when they acquire their characteristic white head and tail.

THE PLIGHT OF THE BALD EAGLE

The first major decline of bald eagles began in the mid to late 1800s, coinciding with the decline of waterfowl, shorebirds, and other prey.

Even though they primarily eat fish, bald eagles were believed to be marauders, preying on chickens, lambs, and domestic livestock. The large raptors were shot in an effort to eliminate a perceived threat. Coupled with the loss of nesting habitat, bald eagle populations declined.

In 1940, noting that the species was “threatened with extinction,” Congress passed the Bald Eagle Protection Act, which prohibited killing, selling, or possess- ing the species. A 1962 amendment added the golden eagle, and the law became the Bald and Golden Eagle Protection Act.

The Phrase "eagle eye" describes the highly developed visual ability of bald eagles, which can spot a moving rabbit almost a mile away. An eagle, flying at 1,000 feet altitude, can spot prey across almost three square miles.

Shortly after World War II, DDT, hailed as a new pesticide to control mosquitoes and other insects, came on the scene. However, DDT and its residues washed into nearby waterways, where plants and fish absorbed it. Bald eagles, in turn, were poisoned with DDT when they ate the contaminated fish.

The chemical interfered with the ability of the birds to produce strong eggshells. As a result, their eggs broke during incubation or failed to hatch. DDT also affected other birds, such as peregrine falcons and brown pelicans.

Although bald eagles may range over great distances, they usually return to nest within 100 miles of where they were raised.
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In addition to the adverse effects of DDT, some bald eagles have died from lead poisoning after feeding on waterfowl containing lead shot, either as a result of hunting or from inadvertent ingestion.

By 1963, with only 417 nesting pairs remaining nationwide, the bald eagle was in danger of extinction.

THE ROAD BACK

As the dangers of DDT became known, the use of DDT was banned in in the United States in 1972. It was the first step on the road to recovery for the bald eagle. Bald eagles were listed under the Endangered Species Act as endangered in 1978 throughout all of the lower 48 states except Michigan, Minnesota, Oregon, Washington, and Wisconsin, where the species was designated as threatened. Bald eagles were not listed as threatened or endangered in Hawaii because they did not occur there, or in Alaska because the populations remained robust there.

“Endangered” means a species is considered in danger of extinction throughout all or a significant portion of its range. “Threatened” means a species is considered likely to become endangered within the foreseeable future, but is not currently in danger of extinction.

By listing bald eagles as endangered, The U.S. Fish and Wildlife Service, other federal and state agencies, and private groups were able to protect the birds. These efforts were improved by captive breeding programs, reintroduction efforts, and protection of nest sites during the breeding season.

Bald eagles mate for life and will only choose another mate if its faithful companion dies. Courting often involves spectacular aerial displays of divings and locking talons.
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In July 1995, bald eagles in the lower 48 states had recovered to the point where those populations previously considered endangered were now considered threatened. In 2006, the bald eagle population was estimated at 9,789 nesting pairs in the contiguous United States. On Aug. 9, 2007, our nation’s symbol was removed from the list of threatened and endangered species. The regal bald eagle is an endangered species success story.

WHAT LIES AHEAD

Although the bald eagle was removed from the list of threatened and endangered species under the Endangered Species Act, it is still protected by the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act. Both laws prohibit killing, selling, or otherwise harming eagles, their nests, or eggs. Guidelines have been developed to help landowners, land managers, and others avoid disturbing bald eagles. These can be found at fws.gov/northeast/ecological/eagle.html.