Green sea turtles navigate thousands of miles using Earth's magnetic field as a built-in GPS.

Green sea turtles (Chelonia mydas) rely on a sophisticated sensory system to navigate the 'lost years' of their youth and adult migrations. Research led by Dr. Kenneth Lohmann at the University of North Carolina has demonstrated that these turtles perceive both magnetic intensity and inclination angles. This dual-sensor capability allows them to create a mental 'magnetic map' of the ocean floor.In a landmark study published in the journal Science in 2001, researchers proved that hatchlings use these magnetic cues to stay within the North Atlantic Gyre. By exposing turtles to magnetic fields mimicking different geographic locations, the scientists observed the turtles swimming in the specific directions needed to stay on course. This behavior confirms they possess a positional sense often compared to a global positioning system.The biological mechanism behind this feat involves magnetite crystals in the turtle's brain or specialized photoreceptors in their eyes. These structures allow the animal to 'see' or feel the Earth's magnetic field lines as they fluctuate across the globe. This precision is vital for 'natal homing,' the process where turtles return to their specific birth site to lay eggs after traveling over 2,000 miles.Even when powerful ocean currents or storms push them hundreds of miles off course, the turtles can recalibrate their heading. This resilience ensures the survival of the species by allowing them to find isolated nesting grounds like Ascension Island. This tiny speck of land in the South Atlantic is only 7 miles wide, yet turtles find it with unerring accuracy every nesting season.