MORA, C.V.*; JOHNSEN, S.; LOHMANN, K.J.; University of North Carolina; Duke University, North Carolina; University of North Carolina: Detection Of Polarized Light By Loggerhead Sea Turtles (Caretta caretta)

Sea turtles have been hypothesized to use polarized light to find their way during migration and to detect food, but efforts to demonstrate such an ability experimentally have yielded inconclusive results. To investigate possible polarization vision in juvenile loggerhead sea turtles (Caretta caretta), we adapted a conditioned choice discrimination method commonly used in animal psychology. The turtles were required to discriminate between two polarized light stimuli, presented side by side in a fully automated experimental arena. The two light stimuli were identical except the plane of polarization was aligned horizontally for one and vertically for the other. The turtles learned to press one of two available paddles depending on whether the stimulus arrangement was horizontal-vertical or vertical-horizontal. Correct choices were rewarded with food and incorrect choices resulted in a time penalty. The turtles clearly discriminated between the two polarized light stimuli. Control experiments, during which the pattern of polarization was disrupted or the plane of polarization was identical for the two stimuli, demonstrated that the polarization patterns, rather than some other element of the stimuli, were the basis for the discrimination. These results provide the first direct evidence that sea turtles can perceive polarized light making loggerhead sea turtles only the second reptile and the first aquatic species to have been shown to do so. This result has important implications for the feeding ecology of sea turtles as perception of polarized light may enable detection of translucent prey. It may also play a role during migration allowing sea turtles to exploit patterns of skylight polarization as an orientation cue.