Washington: Researchers from University of North Carolina at Chapel Hill have finally solved the mystery of how young loggerhead sea turtles find their way back home after a transoceanic migration.
These turtles begin their journey 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.
"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.
"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.
The team found that the turtles pick up on magnetic signatures that vary across the Earth''s surface in order to determine their position in space—both east-west and north-south—and steer themselves in the right direction.
However, they don’t depend 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 and the strength of the magnetic field.
The field lines are parallel to the Earth’s surface near the equator and grow steeper as one reaches the poles. The magnetic field also varies in intensity, being generally strongest near the poles and weakest near the equator.
"Although it is true that an animal capable of detecting only inclination or only intensity would have a hard time determining longitude, loggerhead sea turtles detect both magnetic parameters," Putman said.
"This means that they can extract more information from the Earth''s field than is initially apparent."
Because inclination and intensity vary in slightly different directions across the Earth''s surface, particular oceanic regions have distinct magnetic signatures consisting of a unique combination of inclination and intensity.
The findings may have important implications for the turtles, the researchers say.
"This work not only solves a long-standing mystery of animal behavior but may also be useful in sea turtle conservation," Lohmann said.
"Understanding the sensory cues that turtles rely on to guide their migrations is an important part of safeguarding their environment."
The discovery may also lead to new approaches in the development of navigational technologies, the researchers added.
The study appears on February 24 in Current Biology.
First Published: Friday, February 25, 2011, 15:59