Learned magnetic map cues and two mechanisms of magnetoreception in turtles

Abstract

Overview

Growing evidence indicates that migratory animals exploit the magnetic field of the Earth for navigation, both as a compass to determine direction and as a map to determine geographical position¹. It has long been proposed that, to navigate using a magnetic map, animals must learn the magnetic coordinates of the destination^2,3, yet the pivotal hypothesis that animals can learn magnetic signatures of geographical areas has, to our knowledge, yet to be tested.

Findings

• This study reports that the loggerhead turtle (Caretta caretta), an iconic navigating species, can indeed learn such information.
• When fed repeatedly in magnetic fields replicating those at specific oceanic locations, juvenile turtles learned to distinguish these fields (where they encountered food) from magnetic fields existing elsewhere. This ability could underlie foraging site fidelity.
• Conditioned responses in this new magnetic map assay were unaffected by radiofrequency oscillating magnetic fields, a treatment expected to disrupt radical-pair-based chemical magnetoreception^4-6. This suggests that the magnetic map sense of the turtle does not rely on this mechanism.
• In contrast, orientation behaviour requiring use of the magnetic compass was disrupted by radiofrequency oscillating magnetic fields.

Conclusion

The findings provide strong evidence that two different mechanisms of magnetoreception underlie the magnetic map and magnetic compass in sea turtles. Importantly, this research shows that radiofrequency oscillating magnetic fields can interfere with the magnetic compass behavior of turtles—highlighting a direct link between electromagnetic fields and navigation abilities in animals.