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Homing Instinct: Sea Turtles Rely On Earth's Magnetic Field to Find Their Way Home

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Adult female sea turtles return to their birthplace when it's time to lay their egg and this remarkable ability of these marine animals has something to do with its ability to take advantage of the Earth's magnetic field.

Scientists have long been baffled as to how sea turtles manage to go back to the place of their birth to lay they eggs but a two scientists appear to finally crack part of the answer.

Prior studies provided evidence that sea turtles make use of the Earth's magnetic field to guide them at sea but it was not clear if this also helps them navigate towards their nesting site that their mothers have chosen before.

To investigate, J. Roger Brothers and Kenneth J. Lohmann, both from the University of North Carolina at Chapel Hill, looked at a 19-year database of loggerhead sea turtle nesting along the eastern coast of Florida.

The earth's magnetic field fluctuates over time, which can be attributed to the molten material surrounding the planet's iron core sloshing around, resulting in the magnetic field strengthening in some areas and weakening in others.

The researchers found that there is a strong link between the subtle changes in the magnetic field of the Earth and the spatial distribution of the sea turtle's nests confirming their hypothesis that turtles change their nesting location as the magnetic signatures drift across the shore.

When the magnetic signals from nearby beaches get closer together, for instance, these areas become densely covered by turtle nests. The sea turtles, however, lay in nests that are fewer and farther between each other in places where the magnetic signatures have diverged.

"These findings confirm central predictions of the geomagnetic imprinting hypothesis and provide strong evidence that such imprinting plays an important role in natal homing in sea turtles," the researchers said.

The researchers said that the sea turtles go to the places where they started life because successful nesting needs a number of rare environmental features such as soft sand, few predators, and the right temperature with easy access to the 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."

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