Today we take it for granted that birds migrate — maybe we don’t know where, but we know it’s a fact. Until the past couple of hundred years, though, migration was not a given. In fact, for most of history migration was a persistent and largely unsolvable mystery, with dozens of theories that ranged from the likely to the preposterous.

Until the twentieth century, no one knew why birds disappeared for part of the year, and to where. Technologies such as bird banding, radio tracking and bioacoustics help us solve the many mysteries of bird migration.