Sea turtles are masters of navigation. It begins when hatchlings, only minutes old, find their way from the beach to the sea. Once in the water, they establish a course that will take them on an epic migration. They make this dangerous journey alone, following complex migratory pathways across huge expanses of open ocean without guidance or training.
Loggerhead sea turtles are among the animals that can detect the Earth's magnetic field. Could hatchlings be using this information to maintain their course in the absence of waves?
To answer this question, Lohmann and his colleagues needed hatchling sea turtles, a circular pool, tiny turtle harnesses, and a device that could reverse magnetic fields. Each turtle was fitted with a nylon-Lycra harness. The harness was connected to a monofilament line that tethered the turtle to an electronic tracking system in the center of a circular pool, allowing the turtles to swim in any direction. A large coil system surrounded the pool. The researchers could turn the coil system on to reverse the direction of the magnetic field around the swimming turtles.
Some of the tethered turtles were allowed to swim under normal magnetic field conditions. Others swam in a reversed magnetic field, turned 180° by the coil system. Hatchlings tested in the Earth's normal magnetic field tended to swim east to northeast, the direction they normally follow in their offshore migration. But the turtles tested in the reversed magnetic field swam in the opposite direction, indicating loggerhead hatchlings are able to detect the Earth's magnetic field and use it to orient themselves.