CHAPEL HILL, N.C., Jan. 16 (UPI) -- Every year, adult sea turtles make the journey back to the beaches where they were born. They return year after year to lay their own eggs. Their offspring, freshly hatched, will make their way out to sea. Ten years later, having reached sexual maturity, the sea turtles will return to the same natal beach. The cycle repeats, generation after generation.
Now, new evidence suggests unique electromagnetic signals register with the newly hatched turtles, coordinates that will remain imprinted on their internal electromagnetic compass and guide them back to the sands of their birth.
"Sea turtles migrate across thousands of miles of ocean before returning to nest on the same stretch of coastline where they hatched, but how they do this has mystified scientists for more than fifty years," J. Roger Brothers, a marine biologist at the University of North Carolina at Chapel Hill, said in a recent press release. "Our results provide evidence that turtles imprint on the unique magnetic field of their natal beach as hatchlings and then use this information to return as adults."
Previous studies showed that turtles use magnetic fields while navigating out at sea, but proving infant turtles were born with an electromagnetic imprint was more difficult.
"We reasoned that if turtles use the magnetic field to find their natal beaches, then naturally occurring changes in the Earth's field might influence where turtles nest," Brothers explained.
When Brothers and colleagues compared information from a 19-year database of loggerhead nesting sites along Florida's Atlantic Coast, they found a strong correlation between changes in the Earth's constantly shifting magnetic field and spacing of turtle nests.
In years where magnetic field signatures diverged slightly, turtle nests spread out. The opposite happened with magnetic signatures became more concentrated.
Sea turtles' dramatic nesting journey isn't out of an exhausting reverence for tradition, but because ideal nesting conditions -- soft sands, warm temperatures, easy access, few predators -- are rare.
"The only way a female turtle can be sure that she is nesting in a place favorable for egg development is to nest on the same beach where she hatched," Brothers concluded.
Researchers said the magnetic imprint isn't necessarily an ultimatum. If a rowdy beach hotel is built right next to a nesting site, the turtles would likely move down the beach. But that's unlikely to happen, as the federal government recently extended protections to an additional 685 miles of nesting beaches.
Brothers would like to replicate the research strategy for other animals that take on similar reproductive migrations -- including salmon, sharks, migratory sea birds and elephant seals.
"Our hope is that this analysis will open the door to figuring out how all the other animals are doing it," he told the Los Angeles Times.
The study was published this week in the journal Current Biology.