"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, 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," Brothers said.
    
While earlier studies have shown that sea turtles use the Earth's magnetic field as a guide while out at sea, it has remained unclear whether adult turtles also depend on magnetic features to recognise and return to the nesting sites chosen by their mothers before them.
    
In the new study, Brothers and Lohmann took a different approach by studying changes in the behaviour of nesting turtles over time. "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 investigate, the researchers analysed a 19-year database of loggerhead nesting along the eastern coast of Florida, the largest sea turtle rookery in North America. They found a strong association between the spatial distribution of turtle nests and subtle shifts in the Earth's magnetic field.

The study was published in the Cell Press journal Current Biology.

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