Hatchling sea turtles use surface waves to establish a magnetic compass direction

Hatchling sea turtles emerge from underground nests, crawl to the ocean, and swim away from the land. In shallow water near shore, hatchlings maintain offshore headings by swimming into oceanic waves; in deeper water, however, turtles appear to rely on different mechanisms to maintain their courses. To determine whether loggerhead hatchlings, Caretta caretta L., are able to transfer a course initiated on the basis of waves to a course maintained by a magnetic compass, we studied the orientation behaviour of turtles that had been exposed to waves for either 15 or 30 min before being tested in still water. Hatchlings that swam into waves for 15 min failed to continue swimming on similar courses when the waves were discontinued, but turtles that swam into waves for 30 min maintained similar mean headings after the waves stopped. Inverting the vertical component of the magnetic field during the test period reversed the direction of orientation of this latter group of turtles. Thus, hatchlings can transfer a heading induced by waves to a magnetic compass, and thereby continue to migrate away from land after contact with the coast is lost. Migratory orientation in turtles resembles that of birds in that both rely on multiple cues and an ability to transfer information between various cues and compasses at appropriate times during the journey.Copyright 1998 The Association for the Study of Animal Behaviour.