Natal homing is a pattern of behavior in which animals migrate away from their geographic area of origin and then return to reproduce in the same location where they were hatched. Loggerhead sea turtles are an extreme case of this. They travel long distances from the beaches they were born, on only to return regularly to nest. Not much is known about how this occurs.
One hypothesis is that turtles imprint on the unique geomagnetic signature of the beach they hatched on and use it to come back. Earth’s magnetic field changes over time the period of time the turtles are away so geomagnetic imprinting should cause turtles to change their nesting locations as magnetic signatures drift slightly causing either longer or shorter nesting spaces along the coastline.
A convergence index was created to quantify the degree of movement within each county. Analysis of the relationship between each convergence index and nesting densities from the 19 year data base confirmed the predictions of geomagnetic imprinting. The highest convergence indices were associated with the largest nesting densities. Divergence was also associated with low nesting densities. This was true for all 12 counties.
A similar study done with salmon showed the destination was the same regardless of route, whereas this study shows a change in endpoint due to change in magnetic fields.
These findings confirm and provide strongest evidence to date that sea turtles imprint on the geomagnetic signature of their natal beaches and use it return. The results also confirm the findings of geomagnetic imprinting in salmon and suggest that it is used in natal homing for other animals.
Citation: Brothers. J.R., Lohmann K.J., 2015. Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles, Current Biology, Vol. 25. pg 392-396
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