Eagles, members of the same family as hawks and Old World vultures, are found throughout the world. The bald eagle is the only eagle unique to North America.
An average bald eagle measures 32 to 40 inches (81 to 107 centimeters) long, weighs between 6 and 16 pounds (2.7 and 7.3 kilograms), and has a wingspan up to 7.5 feet (2.3 meters). Females are generally larger than males. The color of the plumage (covering of feathers) on the body is brown.
The distinctive white head and tail feathers appear after the eagle is four to seven years old. The bird has black talons, a yellow beak, and pale eyes. Its diet is composed mainly of fish, although it will eat ducks, rodents, snakes, and anything else it can catch.
Bald eagles are solitary birds that mate for life. Once paired, a male and female eagle build a large nest in the top of a large tree near a river, lake, marsh, or other wetland area.
The birds may use and add to this nest year after year. Some older nests measure 10 feet across. Bald eagles range over great distances, but usually nest within 100 miles (161 kilometers) of where they were raised.
A female bald eagle usually lays 2 to 3 eggs once a year. She then incubates (sits on or broods) them for 35 days until they hatch. The young eagles, called eaglets, fledge (develop flying feathers) within three months and leave the nest about a month afterward.
Because of disease, bad weather, and lack of food, many eaglets do not survive their first year. Those that do survive may live 30 years or longer in the wild.
Habitat and current distribution
Bald eagles prefer to inhabit secluded forests with tall, mature trees and flowing water. Northern eagles usually migrate south during winter to open water areas where food is abundant.
The bald eagle ranges over most of the North American continent, from Alaska and Canada down to northern Mexico. Biologists (people who study living organisms) believe between 80,000 and 110,000 bald eagles currently exist.
History and conservation measures
However, this majestic bird began to disappear from the countryside as settlers carved out more and more of the American wilderness in the nineteenth and early twentieth centuries.
As their habitat shrank, so did their food supply. In addition, they were often shot by farmers and ranchers in the mistaken belief that they were pests or a threat to livestock.
By 1940, the number of bald eagles was so low that Congress passed the Bald Eagle Protection Act. This act made it illegal to kill, harass, possess (without a permit), or sell bald eagles.
Nonetheless, the eagle population continued to decline, especially after World War II (1939–45). The reason was the rampant spraying of the powerful pesticide DDT (dichloro-diphenyl-trichloroethane).
Farmers, foresters, and others used DDT to kill weeds, insects, rodents, and other pests that harmed agricultural crops. However, DDT does not dissolve in water and does not break down chemically in the environment. After being sprayed on cropland, it is washed (through rain and other precipitation) into nearby streams, rivers, and lakes.
The DDT residue is absorbed by aquatic plants and small animals, which are then eaten by fish. In turn, the fish are consumed by bald eagles. At each step higher in the food chain, the DDT residue becomes more concentrated in the fatty tissues of the contaminated animals.
Contaminated bald eagles (and other birds) began laying eggs that had weak shells. The eggs often broke during incubation or did not hatch at all, and the eagle population quickly fell. By the early 1960s, only about 400 pairs of nesting bald eagles existed in the lower 48 states. In some areas, they had disappeared completely.
In 1962, marine biologist and writer Rachel Carson published Silent Spring. The book documented the dangers of pesticides, particularly that of DDT. In large part because of this famous book, DDT was banned for most uses in the United States in 1972.
This ban, coupled with efforts to protect bald eagle habitat, brought the bird back from certain extinction. By 1981, the nesting population in the lower 48 states had doubled.
In July 1995, the U.S. Fish and Wildlife Service officially down-listed the bald eagle on the Endangered Species List from endangered to threatened throughout the nation. On July 6, 1999, the agency officially proposed to delist the bald eagle—that is, to remove it from the endangered species list.
Habitat destruction and illegal hunting still threaten the bald eagle, primarily in the southern part of its range. Most wildlife experts agree, though, that the bald eagle’s recovery is encouraging.