Before European settlers first sailed to America, the bald eagle population was about half a million. They lived along the Atlantic from Labrador to the tip of south Florida, and along the Pacific from Baja California to Alaska. There's no single cause for the decrease in the bald eagle population. As the human population grew, the eagle population declined. The food supplies for eagles decreased because the people hunted and fished over a broad area. Basically eagles and humans competed for the same food, and humans, with weapons, had the advantage. As the human population expanded westward, the natural habitat of the eagles was destroyed, leaving them fewer places to live.
By the 1930s people became aware of the decline in the bald eagle population, and in 1940 the Bald Eagle Act was passed, and eagle populations began to recover, but at the same time DDT and other pesticides began to be widely used. Pesticides sprayed on plants were eaten by small animals, which were later eaten by birds of prey, including the bald eagle. The DDT poison harmed both the adult birds and the eggs that they laid. The eggshells became too thin to withstand the incubation period, and were often crushed. Eggs that we