The surprising recovery of once-rare birds

Sandhill cranes can be spotted in many states, but in the 1930s their populations had crashed to a few dozen breeding pairs in the eastern U.S. Rsocol/Wikimedia Commons, CC BY

When I started bird-watching as a teenager, a few years after the first Earth Day in 1970, several species that once thrived in my region were nowhere to be found.

Some, like the passenger pigeon, were extinct. Others had retreated to more remote, wild areas of North America. In many cases, humans had destroyed their habitat by cutting down forests, draining wetlands and converting grasslands to agriculture. Pesticides such as DDT, air and water pollution, and the shooting of birds added to the drop in numbers.