Meeting Abstract
Diverse animals migrate tremendous distances before returning to reproduce in the same location where they began life. An extreme example of this behavior called natal homing culminates in Ostional, Costa Rica, where hundreds of thousands of sea turtles return to nest in synchrony on a 4km stretch of beach. Despite strong evidence that all sea turtle species display natal homing, little is known about how it is accomplished. One recent idea, known as the geomagnetic imprinting hypothesis, notes that sea turtles detect Earth’s magnetic field and use it to navigate. Moreover, Earth’s field varies across the globe and different geographic areas are characterized by unique magnetic signatures. Thus, hatchling turtles might learn the magnetic coordinates of their natal beach and use this information to return as adults. To investigate a central tenet of this hypothesis, that adult turtles use magnetic navigation to locate the nesting beach, we traveled to Ostional and captured female turtles as they crawled onto the beach. We tethered each turtle in a water-filled arena inside a magnetic coil system designed to precisely control the magnetic field within the arena. We then exposed the turtles to the magnetic signature that exists 500km northwest of the nesting beach, a location within the turtles’ migratory range, and monitored their swimming direction in response. If turtles use Earth’s field to identify their natal beach we expect them to swim southeast in response to this magnetic displacement. Initial analyses confirmed this prediction: in response to the magnetic field that exists 500km northwest of the nesting beach turtles were, as a group, significantly oriented southeast. These preliminary findings are consistent with the geomagnetic imprinting hypothesis and suggest turtles use magnetic navigation to locate their nesting beach.
