Individual differences in the sea-finding mechanism of hatchling leatherback turtles

When hatchling leatherback turtles, Dermochelys coriacea, are unilarerally blindfolded, some circle toward their open eyes and some toward their covered eyes. If tests were performed immediately after one eye had been blindfolded, in cases where the turtle circled toward the open eye there was a transient potentiation of circling at the start of the test. In contrast, in cases where the turtle circled toward the covered eye, circling was decreased at the start of the test. Similar transient phenomena occurred when the position of a blindfold was reversed from one eye to another. Following removal of a blindfold, circling toward the previously covered eye was increased. The transient effects in all these tests waned by about 2 min. There was no evidence of transient circling tendencies in turtles that were tested after a unilateral blindfold had been in position for 4 min. The results suggest that ipsilateral and contralateral retinotectal turning systems differ in strength among individual turtles and individual eyes, and that following unilateral blindfolding there is a potentiation only of the ipsilateral turning system associated with stimulation of the still open eye.