Sea Turtle Sat Nav
Adult sea turtles use memories of the Earth's magnetic field to return and lay eggs on the same beaches they were born on, scientists from North Carolina have discovered.
Sea turtles hatch from eggs laid on the warm beaches of every ocean on our planet. Females are able to relocate the same beach that they themselves were born on, even after swimming across thousands of miles of ocean for up to 30 years before they return.
Many animals use some form of magnetic field memory to navigate. But what wasn't clear was if turtles also rely on this technique when making their way to a beach to lay eggs.
Now, writing in Current Biology, Professor Ken Lohmann from the University of North Carolina has used the natural deviation that occurs over time in the Earth's magnetic field to show that turtles form a memory imprint of the magnetic signature corresponding to their birth beach and use this later to find their way back to breed.
By trawling through 19 years of sea turtle nest data, Lohmann compared the positions of thousands of nests with simultaneous records of the Earth's magnetic field signature at those locations.
And because the Earth's magnetic field is slowly deviating, perhaps as the planet gears up for a magnetic flip which happens roughly every 100,000 years or so, it was possible to show that changes in the Earth's magnetic field were also reflected in similar changes in the positions of the turtles' nesting sites.
"Imprinting is a special type of learning that occurs early in an animal's life and the association lasts for a very long time, sometimes for the rest of the animal's life," explains Lohmann. "Sea turtles imprint on the unique magnetic signatures of their home beaches."
The reason sea turtles return to their home beaches is probably an evolutionary development. The chances of the eggs and hatchlings surviving are very dependent on the environment on the beaches. Therefore, female turtles will return to the same beach they were hatched. According to Lohmann, it's probably a case of "if it was good enough for me, it will be good enough for my offspring..."