Each summer, Smithsonian's National Zoo is flooded with calls from visitors reporting large, brown birds on the loose. What they don't know is these supposed fugitives, black-crowned night-herons, are visitors just like them. The elusive winged tourists have flocked to the zoo for over 100 years, breeding on its grounds and stealing its food for six months at a time. Then, they vanish. Now, join the zoo's caretakers as they attempt to track the mysterious herons' migratory patterns, a crucial step in better understanding these secretive birds.