Article Review: Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles

     Natal homing is a well-known but poorly understood phenomenon that describes the migration and eventual return of animals to a given geographic location.  Loggerhead sea turtles (Caretta caretta) are perhaps the most well known example as they periodically traverse vast distances but return to the same stretch of coastline to reproduce.  It is thought that these sea turtles obtain precise long-distance navigational information via detection of the intensity as well as the inclination angle (the angle at which magnetic isolines intersect at the surface) of Earth's magnetic field.  The authors noted that because the Earth's magnetic field changes slightly over time, so should the location of the geomagnetic imprint believed to be used by the loggerhead sea turtles to return to their previous natal area.

     To investigate this phenomena, the authors of this study referenced a 19-year database (1993-2011) of loggerhead nesting sites along Florida's Statewide Nesting Beach Survey, the largest sea turtle rookery in North America.  They argued that two parameters, intensity and inclination angle, change predictably across the surface of the Earth, creating a pattern of isolines that could be used to distinguish between areas of coastline (Fig. 1).  Their hypothesis predicted that converging isolines of intensity or inclination would be followed by a convergence of natal locations between those respective isolines (i.e. an increase in natal location density along a shorter area of coastline). Conversely, areas of diverging isolines would be followed by a divergence in natal locations or a decrease in natal location density along a longer area of coastline.
   
     The results of this article strongly suggest that loggerhead sea turtle navigation is partly a function of magnetic field intensity and/or inclination angle.  The authors argue that this article provides the strongest and most detailed evidence of geomagnetic imprinting in loggerhead sea turtles in response to a fluctuating external magnetic field to date and that their evidence is suggestive of other animals such as fish, birds, and mammals that could also exhibit similar adaptations.

     The loggerhead sea turtles' uncanny ability to use magnetic navigation and geomagnetic imprinting to accomplish natal homing is eons ahead of our current understanding of magnetic navigation.  Further research is needed to unlock the secrets behind these age old mechanisms that could one day spark a revolution in human navigation.        

Brothers, J. Roger, and Kenneth J. Lohmann. "Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles." Current Biology 25.3 (2015): 392-96. Web.