Americans were shocked to discover that the national bird was in danger of disappearing from the skies forever. Studies in 1970 showed only about 1,000, or fewer, bald eagles(秃鹰) in the country.
The major cause of the problem was people. The spread of civilization(文明) destroyed many of the eagles' feeding and nesting areas. And the eagles were being affected by D-D-T and other insect poisons. The poisons were in the animals the eagles ate. They reduced the eagles' ability(能力) to use calcium(钙). This made the outside of the eagles' eggs very thin. Often, the eggs broke before baby birds were developed.
In 1972, the U. S. government banned(禁止) D-D-T. People also became interested in protecting places where eagles live. And stronger efforts were made to carry out laws protecting the birds. Scientists began a program that placed baby bald eagles which were born under human care, into nests of wild bald eagles. Often, the wild birds accepted the babies.
These efforts appear to have been successful in saving the American bald eagles. Today the number of the bald eagles has increased to more than 11, 000.
