The flight paths of migrating birds can span continents. Honeybees zigzag through orchards and meadows to the sweetest spots for nectar and then zip back home again. Adult salmon, in what might be the most epic voyage in the animal kingdom, swim from the ocean upstream through branching and churning rivers to lay eggs in the spot where they were born. It’s a route they took only once before — in the opposite direction, as young fish — and yet they don’t get lost.
Obviously, none of these animals, which range from invertebrates to mammals, rely on Google Maps. Instead, they seem to be reading some invisible clues in the environment. People throughout history have tried to solve the mystery. Now researchers are being drawn to some powerful clues.
