The captive-bred northern bald ibises at Austria’s Konrad Lorenz Research Station hadn’t left the facility for generations. So biologists were stunned when the flock tried to migrate in August 1997, abruptly taking flight and scattering in a frenzied movement. The scientists had never imagined that their birds, extinct in the wild in Europe for more than 300 years, retained the instinct. Inspired by the birds’ behavior— and the movie Fly Away Home, in which a duo leads orphaned Canada geese south by air—Johannes Fritz began plotting a bold reintroduction plan. Fritz, then a grad student at the research station, swallowed his motion sickness, earned a pilot’s license, bought an ultralight plane, and began guiding the hitherto captive birds from their ancestral Austrian breeding grounds to Italian overwintering sites. Today, after a decade of trial and error, Fritz and his colleagues have a flock of 20 migratory ibises. Fueled by a new $5.9 million grant from the...