Not long ago, bald eagles faced a bleak future. Heavily hunted before receiving federal protection in 1940, their numbers fell even further in the 1970s when the pesticide DDT caused females to lay thin-shelled eggs that broke easily. In 1980, biologists spotted only three bald eagle nests in Pennsylvania. Through hugely successful conservation efforts, bald eagle numbers have dramatically risen, and in 2011 researchers found 217 nests across the state.