The magnetic map of hatchling loggerhead sea turtles

Young loggerhead sea turtles (Caretta caretta) from eastern Florida, U.S.A., undertake a transoceanic migration in which they gradually circle the North Atlantic Ocean before returning to the North American coast. Hatchlings in the open sea are guided at least partly by a 'magnetic map' in which regional magnetic fields function as navigational markers and elicit changes in swimming direction at crucial locations along the migratory route. The magnetic map exists in turtles that have never migrated and thus appears to be inherited. Turtles derive both longitudinal and latitudinal information from the Earth's field, most likely by exploiting unique combinations of field inclination and intensity that occur in different geographic areas. Similar mechanisms may function in the migrations of diverse animals.

► Loggerhead turtles navigate using the Earth's magnetic field. ► Turtles inherit a magnetic map that guides their first transoceanic migration. ► Magnetic fields unique to key ocean areas trigger changes in migration direction. ► Young turtles direct their migration and do not merely drift as once thought.