Juvenile and adult sea turtles often navigate to specific feeding areas during long-distance migrations, and adults periodically return to particular geographic areas for mating and nesting. In addition, turtles displaced from feeding or nesting areas often home to the site of capture. Relatively little is known, however, about how turtles navigate to particular goal areas. Both juvenile and adult turtles use the Earth's magnetic field as a source of navigational information. Laboratory experiments have provided evidence that juvenile green turtles learn the magnetic topography of their feeding grounds and acquire a “ magnetic map ” that facilitates navigation toward particular locations. Adult green turtles displaced from nesting beaches on an island in the Indian Ocean showed diminished homing ability when magnets were attached to their heads, implying that mature turtles also exploit magnetic cues when navigating to islands or other specific destinations. Although geomagnetic information appears to be an important component of sea turtle navigation, it is unlikely to be the only cue used. Additional experiments in which nesting green turtles were displaced from islands have highlighted the possible involvement of local, non- magnetic cues in the final phase of island-finding. Thus, a reasonable hypothesis is that turtles use multiple cues to navigate in the marine environment, perhaps relying on a magnetic map to navigate into the vicinity of a distant target and then using non-magnetic cues to guide themselves to the final goal.
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