No place like magnetic home: Sea turtles have a 'GPS' that uses Earth's magnetic field

Sea turtle with magnet
CC BY-SA 2.0 Flickr

Beach Sweet Beach

Many animals have a talent for finding their way around the globe that any of us who gets lost doing a short trip can't help but envy. From birds who go back and forth across continents, following the seasons, to the beautiful sea turtles that can find the specific beach where they were born years before to, in turn, lay their eggs. For decades, scientists have wondered how the turtles did it, and it seems like we might finally have an answer thanks to a study conducted at the University of North Carolina at Chapel Hill.

Sea turtlesFlickr/CC BY 2.0

“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,” said J. Roger Brothers of the University of North Carolina at Chapel Hill. “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.”

To prove that this is the case, the resarchers compared 19 years of data on Loggerhead Sea Turtle migration on the Eastern coast of Florida with data on naturally occurring local changes in the Earth's magnetic field. The scientists found a strong association between the spatial distribution of turtle nests and subtle shifts in the Earth’s magnetic field.

The effect went both ways: When the magnetic fields shifted in such a way that adjacent locations along the beach moved closer, the turtles came back to nest closer together, spreading over a shorter stretch of the coast. When the magnetic signature of certain spots moved apart, the turtles spread out over a longer stretch.

Little is known about how turtles detect the geomagnetic field, but at least we can now show with a fair amount of certainty that they use it.

But why have sea turtles evolved to go nest where they themselves hatched? It's all about finding the right conditions; 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 said. “The logic of sea turtles seems to be that ‘if it worked for me, it should work for my offspring.’”

And yes, I'm aware that the Global Positioning System (GPS) that we use to get around doesn't use magnetic fields, but rather Einstein's relativity (there's an explanation here). Using it in the title was just short-hand for a way to navigate to your destination.

Via Journal of Current Biology, Livescience

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