How Turtles Find the Sea


Departments of Zoology and Psychology, University of Toronto, Toronto, Ontario M5S 1A1, Canada.

Abstract and Summary

Hatchling turtles, after emerging from their nests on the beach, move towards the sea. One explanation of this sea-finding ability is that there is a complex phototropotactic reaction to light; this initiates turning until sub-components of the system receive equal input. Another explanation is that the direction of peak excitation is located instantaneously and that the turtles then head in that direction. This paper reports new experiments on the behaviour of loggerhead turtles (Caretta caretta) wearing partial blindfolds: their poor orientation, even after several hours time for adaptation to the blindfolds, supports the phototropotaxis hypothesis. Data on loggerhead, leatherback (Dermochelys coriacea) and green turtle (Chelonia mydas) hatchlings released under clear skies confirm that the position of the sun does influence orientation. Experiments on loggerheads with wax paper over their eyes show that form vision is not essential for sea-finding. The possibility of mechanisms additional to and redundant with a complex phototropotactic system or a direction locating system are considered but rejected as unlikely.