Arriving on Inaccessible Island—after the inevitable odyssey of getting there—you hear the sound of the Inaccessible Island rail everywhere. The smallest flightless birds in the world, the rails scurry around the vegetation, feasting on worms, berries, seeds, and invertebrates, including a flightless species of moths. During a fieldwork trip in 2011, it took days for Martin Stervander, then a doctoral student at Sweden’s Lund University, to spot one. Even then, “you see something little and dark, running for a second, and that’s about it,” he says.

Catching one, though, proved easy. Usually, when trapping birds, scientists rig a net high off the ground, but for these flightless birds, the net went low. When they played a recording of the bird’s call, it took only a few minutes before a male and female ran straight into the net.

Inaccessible Island rails live only on Inaccessible Island; it appears, as far as any evidence shows, that they never even made it to the neighboring Nightingale Island. “No one really knew the history,” says Stervander, now a postdoctoral research fellow at the University of Oregon’s Institute of Ecology and Evolution. With a sample of a rail’s genetic material, he aimed to finally answer the most mysterious question about these birds: How did they get to Inaccessible Island to begin with?