For years, the Darién Gap, a narrow strip of pristine rain forest connecting Central and South America, was occupied by the Revolutionary Armed Forces of Colombia–People’s Army, or FARC, making it far too dangerous for any scientist to visit. But in 2016, after FARC negotiated a cease-fire with the Colombian government, the gap became far safer, and Wouter Halfwerk, an ecologist from Vrije University Amsterdam, wasted no time in visiting. He started looking for the túngara frog, a small, warty species that he had been studying in Panama for years. And to his surprise, he couldn’t find any.
Halfwerk had spent years in Gamboa, a town that houses people who work at the nearby Panama Canal. In that urban setting, túngara frogs find you. “They come up to your house, and if you approach them, they just keep on calling. You can just pick them up easily,” says Halfwerk. But in the forests of Darien, “it was like looking at a completely different species.” The forest individuals were shier, more elusive, and more easily disturbed than their urban cousins. And, as Halfwerk and his colleagues showed, they sound different, too.
Túngara frogs have some of the best-studied calls in the animal kingdom. Considering that the frog is just an inch long, its call is roughly as loud as a hair dryer, or a ringing phone. And while most frog calls consist of a single repeated chirp or ribbit, male túngara frogs have two elements: a downward whine, followed by one or more chucks. The more chucks a male adds, the more complex and extravagant his song becomes, and the more attractive he is to females. “We compare the call to a peacock’s tail,” Halfwerk says.