If you splashed down in the Atlantic, you'd flounder on which way to swim. But a hatchling loggerhead turtle would know just where to paddle—by reading the Earth's magnetic field. Scientists knew turtles can pinpoint latitude this way. Because the field varies a lot from north to south. But not east to west. So how do turtles know which side of the Atlantic they're on?

To find out, researchers strapped hatchlings into custom Lycra bathing suits, tethered to a tracking unit. They plopped each turtle into a small pool surrounded by magnetic coils. And they replicated the magnetic fields of Puerto Rico and the Cape Verde Islands, two points along the turtles' migration, with equal latitudes but different longitudes. The hatchlings swam opposite directions in the two trials—both being the right ones, to stay on the migratory track. The study appears in the journal Current Biology. [Nathan Putman et al., "Longitude Perception and Bicoordinate Magnetic Maps in Sea Turtles"]

The researchers say turtles may calibrate their migratory maps by sensing the magnetic field's intensity, and its inclination to the Earth's surface—a combo that gives each point of the migration a unique signature. As for any human navigators out there, you'll just have to shell out for a GPS.