The year was 1902. Paul Bartsch, a mollusk researcher at the Smithsonian Institution, wondered whether the aquatic snails he was studying could be spread from one body of water to another by aquatic birds. To find out, he needed to track the movements of birds. Bartsch hatched a plan. He fastened lightweight aluminum rings inscribed with the year, a serial number and a Smithsonian return address around the legs of 23 nestling black-crowned night herons that he captured along the Anacostia River outside Washington, D.C. And then Bartsch waited for news of the banded birds—where they were sighted, what had become of them.