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  • On August 9, 2007, the bald eagle (Haliaeetus leucocephalus) was officially removed from the list of threatened and endangered species. This remarkable achievement required many threads to come together, including the publication of a ground-breaking book, the creation of a list of endangered species, a growing political movement, and the formation of the EPA.

    When the bald eagle was adopted as the national bird of the United States in 1782, there were as many as 100,000 of them soaring in the skies across the country. However, by 1940 their populations had begun to decline. The Bald Eagle Protection Act, which prohibited the eagles from being killed, sold, or kept in captivity, failed to stop the decline.

    The reason for this continued decline was largely unknown, until the publication of Rachel Carson’s book Silent Spring in 1962 offered a clue. Carson warned of the effects of the pesticide DDT, which was in wide use in the U.S. at the time. She presented evidence that DDT contaminated water and the fish that lived in it. When prey birds, such as bald eagles, ate those animals, the DDT accumulated in their fatty tissues. DDT affected the strength of the birds’ eggshells. Thinner, more fragile shells would break prematurely, resulting in fewer baby eagles hatching successfully.

    As environmental activism grew, Congress passed the first Environmental Protection Act in 1966. The following year, the first list of federally protected endangered species was created and included the bald eagle. Growing concern about the environment also led to the establishment of the Environmental Protection Agency in 1970. Though being on the endangered species list provided benefits such as the protection of the eagles’ nesting areas, the true turning point for the bald eagle came in 1972, when the newly formed EPA banned the use of DDT in the United States. After the banning of DDT, bald eagle populations began to recover, resulting in their delisting in 2007.

    1. Despite dramatic success stories suchas that of the bald eagle, only about one percent of the animals on the endangered and threatened species list have recovered enough to be removed from the list. On the other hand, fewer than one percent of the animals on the list have gone extinct. Based on these numbers, do you think the list is effective? Why or why not? 

      Answers will vary depending on how students interpret the purpose of the list. If they see the primary purpose of the list as trying to get as many animals as possible recovered enough to remove, then they may argue that the list is ineffective because most species don’t recover enough to make it off the list. On the other hand, if they see the purpose of the list as preventing the extinction of the animals on the list, they may argue that the list is effective because it has had about a 99 percent success rate in preventing the extinction of the animals on the list, and over half the species on the list now have populations that are stable or growing.

    2. The banning of the pesticide DDT was one of the main factors in the recovery of the bald eagle. What are some other chemicals that have been banned by the EPA? What factors go into making the decision to ban or restrict a chemical?

      Students may mention any of a long list of chemicals banned or restricted by the EPA. Many factors go into the decision to ban or restrict a chemical. These include the intended use of the chemical, the hazards it represents to human health or the environment, and other factors such as persistence and bioaccumulation. The EPA may only use risk factors in their evaluation. They may not use other factors, such as cost/benefit. Public comment and information provided by scientists and relevant industries are also taken into account. 

    3. What role did the food chain play in how DDT affected bald eagles?

      Fish were exposed to DDT when runoff from its application entered streams, rivers, and lakes. When bald eagles ate the fish that had been exposed, they took the DDT into their bodies. Since they were higher up on the food chain and ingested multiple fish that had been exposed, they developed high concentrations of the chemical.

  • Term Part of Speech Definition Encyclopedic Entry
    DDT Noun

    (dichloro-diphenyl-trichloroethane) toxic chemical used as an insecticide but illegal for most uses in the U.S. since 1972.

    delist Verb

    to remove from a list.

    endangered species Noun

    organism threatened with extinction.

    Encyclopedic Entry: endangered species
    Endangered Species Act Noun

    (1973) U.S. legislation that protects endangered species when they are threatened by human activity.

    Environmental Protection Agency (EPA) Noun

    U.S. government organization whose mission is to "protect human health and the environment."

    population Noun

    total number of people or organisms in a particular area.

    premature Adjective

    happening before the expected time.

    Rachel Carson Noun

    (1907-1964) American biologist and author.

    threatened species Noun

    organism that may soon become endangered.