From the very first moments of life, hatchling loggerhead sea turtles have an arduous task. They must embark on a transoceanic migration, swimming from the Florida coast eastward to the North Atlantic and then gradually migrating over the course of several years before returning again to North American shores. Now, researchers reporting online on February 24 in Current Biology, a Cell Press publication, have figured out how the young turtles find their way.
"One of the great mysteries of animal behavior is how migratory animals can navigate in the open ocean, where there are no visual landmarks," said Kenneth Lohmann of the University of North Carolina at Chapel Hill.
"The most difficult part of open-sea navigation is determining longitude or east-west position. It took human navigators centuries to figure out how to determine longitude on their long-distance voyages," added Nathan Putman, a graduate student in Lohmann's lab and lead author of the study. "This study shows, for the first time, how an animal does this."
It appears that the turtles pick up on magnetic signatures that vary across the Earth's surface in order to determine their position in spaceboth east-west and north-southand steer themselves in the right direction. Although several species, including sea turtles, were known to rely on magnetic cues as a surrogate for latitude, the findings come as a surprise because those signals had been considered unpromising for determining east-west position.
The loggerheads' secret is that they rely not on a single feature of the magnetic field, but on a combination of two: the angle at which the magnetic field lines intersect the Earth (a parameter known as inclination) and the strength of the magnetic field.
Near the Equator, the field lines are approximately parallel to the Earth's surface, Putman and Lohmann explained. As one travels north from the Equator, the field lines grow progressively steeper u
|Contact: Elisabeth Lyons|