Biologists estimate that there were up to 500,000 bald eagles in North America when the first European Settlers began arriving. By 1963, there were only 4,017 nesting pairs left in the contiguous U.S., with most of the birds concentrated in 5 states. Bounties and loss of habitat were initially the causes of the diminishing numbers. But the 1940s saw the introduction of pesticides such as DDT into the bald eagle population. With DDT entering the food chain via waterways, females consuming contaminated fish laid eggs with extremely thin shells that were easily broken. After a few decades, much like the Osprey and the Peregrine Falcon, the national symbol of a nation was nearly driven to extinction by chemicals.
In 1973 the Endangered Species Act was created and the bald eagle was given protection under the new law. It was listed as an endangered species in 43 of the lower 48 states in 1978. Thanks to the banning of DDT, stronger environmental laws, greater public awareness and programs to create and maintain habitat, the bald eagle is making an amazing comeback. Today there are about 7,000 nesting pairs in the continental U.S., and bald eagles now nest in every state in the lower 48 except Vermont.