Bald eagles are the national symbol of the United States. But in the 1960s, they nearly became extinct across much of the country. The main culprit was DDT, a chemical that farmers used to kill pests on crops. When eagles ate animals that had eaten DDT, the chemical weakened their eggshells. As a result, their chicks didn’t survive.
“The population was in free fall,” says Bryan Watts, a bird biologist in Virginia. In 1963, only
487 eagle pairs were nesting in the continental U.S. After DDT was banned in 1972, bald eagles slowly started to recover. Now, scientists think more than 10,000 pairs nest in trees from California to Florida to Maine.