For years, scientists have told us that Florida’s female sea turtles faithfully return to nest on the beach where they were born. Now it turns out there’s more to the story. Like many other migrating creatures, sea turtles may have a type of physiological magnetism that acts as a geographic homing device – called geomagnetic imprinting. Two studies – one from 2015 and one from 2018 – found that sea turtles seem to be attracted to the specific magnetic signature of the area where they were born. After roaming the ocean for thousands of miles over 10 to 15 years, females head back to land to lay eggs. In making their remarkable global journey, sea turtles may be magnetically in tune with the molten metal core inside the Earth. Since this internal layer of molten metal tends to slosh around slowly over time as the Earth spins (it even has a jet stream,) the magnetic fields can shift as well.
In doing their studies on Florida’s east and west coasts, University of North Carolina biologists J. Roger Brothers and Kenneth Lohmann compared Loggerhead sea turtle nesting data with magnetic readings and genetic data. Among their conclusions: Female sea turtles return to nest on a beach where the magnetic field is the same as when they were born. If the field which geomagnetically imprinted on them at birth has shifted, they will follow it, and may end up nesting on a different beach – not necessarily the same one where they were born. Surprisingly, sea turtles who nested on beaches with similar magnetic fields turned out to be more closely related genetically to one another than they were to sea turtles who nested geographically closer. Also, where magnetic fields shifted farther apart, there were fewer turtle nests, and where magnetic fields converged, nesting populations were more dense.
Florida’s peninsula is unique among other nesting areas around the globe, because there are similar magnetic fields on both the east and west coasts, researcher Brothers said. New research in Costa Rica, he said, focuses on behavioral tests. In those experiments, biologists work with magnets to determine how olive ridley sea turtles respond.
“There are so many things that animals can do that we can’t,” Brothers said. “And we walk around all the time thinking we’re so smart.”