The bald eagle (Haliaeetus leucocephalus), also known as the American eagle, is the national bird of the United States. This large bird preys on fish and waterfowl and lives in marine or coastal environments. The distinctive white head and tail of mature birds, coupled with wingspans of up to eight feet, make the bald eagle striking and easily identifiable (Sibley, 2000). It is at the center of the Great Seal of the United States and is also prominent on the country's currency.
Despite its symbolic importance to the United States, the bald eagle was nearly extinct by the 1970s due to hunting, loss of habitat, and the use of dichlorodiphenyltrichloroethane (DDT). The practice of paying bounties on eagles that had been killed was relatively common in Alaska. From 1917 to 1952, the Alaska Territory paid bounties on more than 128,000 eagles (U.S. Fish and Wildlife Service, 1993).
A more widespread cause of the population decline was degradation of the eagles' habitat, including increased construction and contamination of water supplies, which reduced the availability of food and nesting areas. Eagles require significant room for nesting; nests can reach nine feet in diameter.
The most acute and serious threat to the bald eagle was the widespread use of DDT as an insecticide. Edmund Russell (2001) outlined the development of DDT by the federal government, initially as a means of eradicating mosquitoes in the Pacific theater during World War II. After the war, DDT entered widespread civilian use. Because of its chemical composition, DDT does not decompose but instead accumulates in tissue. As fish eat contaminated insects, and eagles eat the fish, the concentration of DDT in the birds themselves reaches toxic levels. This toxicity manifests itself in damage to the central nervous system and in the formation of shells that are too weak or soft to protect embryonic birds. In 1963, an estimated 417 breeding pairs remained in the continental United States (FWS, 2008).
By the early 1970s, the Department of Agriculture had begun restricting the use of DDT. Beans (1996) asserts that the 1972 Environmental Protection Agency (EPA) ban on domestic use of DDT was more beneficial to the bald eagle than the passage of the Endangered Species Act of 1973. The ban on domestic DDT use did not immediately improve the prospects for the bald eagle; in 1978, the birds remained listed as endangered in 43 of the lower 48 states and were considered threatened in the remaining five.
Throughout the 1980s and 1990s, however, the eagle population increased substantially. The U.S. Fish and Wildlife Service introduced a plan to remove the species from both the endangered and threatened lists. As of 2007, with almost 10,000 breeding pairs in the continental United States, the bald eagle is no longer listed as either endangered or threatened under the Endangered Species Act. However, the Bald and Golden Eagle Protection Act of 1940, a less-stringent set of protections, remains in force.
See also DDT; Endangered Species Act of 1973
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