Bald Eagles
Zoo Animals
Bald Eagle - Haliaeetus leucocephalus
The Bald Eagle is the only eagle unique to North America. It has been celebrated as our national symbol since 1872, when it ranged over most of the continent from Alaska and Canada, south to Florida and northern Mexico. Benjamin Franklin objected to this bird as our national symbol, accusing the Bald Eagle of “bad moral character” because of its habits of stealing fish from ospreys and scavenging carrion. It’s scientific name, Haliaeetus leucocephalus, means “sea eagle with a white head.” Like all other sea eagles, the bald eagle lives near water and relies on its powerful wings and talons to hunt and seize fish, which comprises about 90% of its diet. Once rare and doomed to become extinct in North America, the bald eagle has made a tremendous comeback.
Wildlife experts believe that there may have been 25,000 to as many as 75,000 nesting bald eagles in the lower 48 states when the bird was adopted as our national symbol in 1782. Since that time, the bald eagle has suffered from habitat destruction and degradation, illegal shooting, and contamination of its food source, most notable due to the pesticide DDT. Bald Eagles have few natural enemies. However, they do need an environment of quiet isolation which includes tall, mature trees and clean water. These conditions have changed over much of the bald eagle’s former range. Although fierce predators, these birds also became prey themselves. Although primarily fish and carrion eaters, bald eagles and other raptors were seen as marauders that killed chickens, lambs and other domestic livestock. As a consequence, large numbers were shot by farmers, ranchers, and bounty hunters. Concerned that the bald eagle was threatened with extinction, Congress passed the Bald Eagle Act in 1940 which made it illegal to kill, harass, possess (without a permit), or sell bald eagles. In 1967, bald eagles were officially declared an endangered species under a law that proceeded the Endangered Species Act of 1973 in all areas of the continental United States.
The greatest threat to the bald eagle’s existence arose from the widespread use of DDT and other pesticides after WWII. DDT was sprayed on croplands throughout the country and its residues washed into lakes and streams. There, the chemicals were absorbed by aquatic plants and small animals that were eaten by fish. The contaminated fish, in turn, were consumed by bald eagles. DDT interfered with the bald eagle’s ability to develop strong shells for its eggs. As a result, bald eagles, and many other bird species, began laying eggs with shells so thin that they often broke during incubation or otherwise failed to hatch. As the dangers of DDT became known, it was banned for most uses in 1972. In addition to the adverse effects of DDT, bald eagles also died from lead poisoning as a result of feeding on hunter-killed or crippled waterfowl containing lead shot and from lead shot that was inadvertently digested by waterfowl.
The U.S. Fish and Wildlife Service, along with other federal and state government agencies, began various recovery methods for the bald eagle in the late 1960s. With these efforts, a devotion to habitat improvement and banning the use of DDT bald eagle populations have steadily increased. From a low of 450 nesting pairs in the lower 48 states, the recovery efforts have now given the U.S. nearly 4500 adult nesting pairs and an unknown number of young and sub-adults.
One of the largest raptors in North America, the bald eagle weighs from 8-13 pounds. Like all raptors, the bald eagle is reverse sexually dimorphic with the female being larger than the male. Also like other raptors, the bald eagle has binocular vision, a strong, hooked beak, and powerful talons and feet that can exert a closing force of 200 pounds per square inch. The wingspan can be 7-8 feet across, and the body length can be as long as three feet from beak to tail. Juveniles are uniformly dark brown or mottled in coloration, with dark beaks, talons, and eyes. In flight, the underside of the juvenile’s wings may be streaked or mottled with white feathers. The bald eagle is not “bald,” rather its name comes from the white feathers over the entire head. After five to six years, the birds achieve full adult plumage and coloring which includes a brilliant white head, neck, and tail, bright yellow beak and feet, and pale yellow eyes. An eagle’s eyes possess vision 10-20 times better and more powerful than human vision. As an example, a bald eagle could perch on one end of a football field and be able to read a newspaper at the other end of the field (100 yards). In flight, the bald eagle holds its wings flat when soaring high in the sky, unlike vultures and other large birds whose wings are held in a dihedral position.
Bald eagles are believed to live 30 years or longer in the wild and up to 50 years in captivity. They mate for life and build huge nests that they return to every year in the tops of large trees near rivers, lakes, marshes, and other wetland areas. The nest is usually constructed out of large and small sticks and lined with grasses in a tall, living tree. Additions are usually made to the nest annually, with some eventually reaching 10 feet across, 20 feet deep, and weighing more than 3000 pounds. Although bald eagles may range over great distances, they usually return to nest within 100 miles of where they were raised. Bald eagles normally lay two-three eggs once a year during the winter months; in South Carolina, it is usually in January. The eggs are incubated by both parents and hatch after about 35 days. The young eagles will first fly at about three months and will fledge about a month later. However, disease, lack of food, bad weather, or human disturbance can kill many eaglets. Sometimes, only about half will survive their first year.
