In 2016, the government of Colombia signed a peace accord with the rebel group known as FARC, bringing an end to six decades of armed conflict that reportedly claimed more than 260,000 lives. It was a historic agreement that earned a Nobel Peace Prize for Juan Manuel Santos, the country’s president at the time. Almost immediately, though, a destructive side effect of the truce became apparent. As FARC fighters cleared out of their remote forest strongholds, miners, loggers, farmers, and others rushed in. Illegal land clearing accelerated. In the year after the peace deal, Colombia lost more than 1 million acres of tree cover, according to the World Resources Institute—a 46 percent increase from 2016. Such rampant deforestation is bad for the global climate, bad for soil fertility, and bad for wildlife. And in particular, researchers now report, it’s bad for Prothonotary Warblers. While some migratory birds fan out across multiple areas of Central or South America in the...