Every spring, for as long as records have been kept, a crowd of hundreds of black crowned night herons descend on the Smithsonian’s National Zoo, mating, eating and generally causing a ruckus. Many of the keepers at the zoo enjoy them, but they can be a tough bird to love.

Every fall, peace is restored when the herons decamp and fly off to… where? For more than a century, nobody knew. Until now.