This year we're celebrating #ESAat50 — the 50th anniversary of the Endangered Species Act, which is one of the world's most powerful legal tools for protecting species at risk of extinction. Up today? Bald eagles. By the early 1970s, bald eagles were nearly extinct in the United States, with the USFWS reporting in 1963 that fewer than 500 nesting pairs of bald eagles remained. The biggest threat? The pesticide DDT, which poisoned the birds when they ate contaminated fish. DDT also thinned the shells of their eggs, leaving many of them so fragile they broke or failed to hatch. Fortunately, the Environmental Protection Agency banned most outdoor uses of DDT in 1972. The Fish and Wildlife Service also federally protected these iconic beauties under the Endangered Species Act, which helped support them in their recovery. Bald eagles have made a remarkable comeback in the past several decades — so much so that they were delisted in 2007. There are more than 300,000 of them in the lower 4...