FIGURE 2 | Evidence for a magnetic map in sea turtles.

From the following article:

The physics and neurobiology of magnetoreception

Sönke Johnsen & Kenneth J. Lohmann

Nature Reviews Neuroscience 6, 703-712 (September 2005)


The physics and neurobiology of magnetoreception

Juvenile sea turtles establish feeding sites in coastal areas and home back to these sites if displaced126, 127. To investigate how turtles navigate to specific sites, juvenile green turtles (Chelonia mydas) were captured in their coastal feeding areas near Melbourne Beach, Florida, USA ('test site' on map). Each turtle was tethered to an electronic tracking system and placed in a pool of water. The pool was surrounded by a magnetic coil system that could be used to replicate the magnetic fields that exist at two distant sites (marked by blue dots). In the circles, each black dot represents the mean direction of one turtle. The arrow in the centre of each circle indicates the mean angle of the group. The dotted lines indicate the 95% confidence interval for the mean angle. Turtles exposed to a magnetic field that exists approx330 km north of their feeding grounds oriented southward, whereas those tested in a field that exists an equivalent distance to the south swam north. Therefore, turtles responded to each field by swimming in the direction that would have led towards the feeding area had they actually been in the locations at which the magnetic fields exist. The results indicate that sea turtles have a type of 'magnetic map' that facilitates navigation to specific geographical areas. Modified, with permission, from Ref. 14 © (2004) Macmillan Magazines Ltd.

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