Adult female sea turtles are literally magnetically drawn to the comforting beaches where they were hatched, finds new research.
What’s more, scientists suspect that tiny magnetic particles in sea turtle brains enable them to detect unique magnetic signatures given off by beaches, such that they can return to them after ultra long journeys.
The findings, published in the latest issue of the journal Current Biology, help solve a long-standing mystery.
“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,” co-author J. Roger Brothers of the University of North Carolina, Chapel Hill, said in a press release.
“Our results,” continued Brothers, “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.”
Prior research determined that sea turtles use the Earth’s magnetic field as a guide while out at sea. It wasn’t clear, though, whether adult female turtles also used this technique to identify and return to the nesting sites chosen by their mothers.
What’s good for mother turtle is good for her adult offspring too, since the latter don’t bother trying to hunt down better beaches. Mom’s choice is the only one.
“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 said.
To test this out, the researchers analyzed a 19-year database of loggerhead nesting sites along the eastern coast of Florida, which has the largest sea turtle rookery in North America. The scientists found a strong association between the spatial distribution of turtle nests and subtle shifts in the Earth’s magnetic field.
For example, in some cases the Earth’s field shifted so that the magnetic signatures of adjacent locations along the beach moved closer together. When that happened, nesting turtles packed themselves along a shorter stretch of coastline. In places where magnetic signatures diverged, sea turtles spread out and laid their eggs in nests that were fewer and farther between.
As for why they go to all of this trouble, successful nesting requires a combination of rare features: soft sand, the right temperature, few predators, and an easily accessible beach.
“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 explained. “The logic of sea turtles seems to be that if it worked for me, it should work for my offspring.”
Photo: A loggerhead sea turtle nesting in the Archie Carr National Wildlife Refuge in Melbourne Beach, Florida. Credit: J. Roger Brothers