Optic orientation in hatchlings of the sea turtle, chelonia mydasI. Brightness: Not the only optic cue in sea‐finding orientation

Abstract

1. On a breeding ground for sea turtles in Surinam the horizontal vector diagram of the radiation field was measured. The mean orientation direction of sea‐finding hatchling green turtles (Chelonia mydas) was not related to the largest horizontal vector (brightest direction).

2. Hoods were designed to hold attachments which would interfere with vision.

3. The seaward orientation was disrupted in turtles with both eyes blindfolded for at least 24 hours. These animals showed a tendency to move down the slope of the beach.

4. Turtles with one eye blindfolded for more than 2 hours oriented seawards.

5. Sea‐finding orientation in the green turtle cannot be explained solely in terms of some photic (e.g. tropotactic) mechanism which permits progress in the brightest direction. In all probability the animal also orients visually with the help of a “multiple input unit system”; (Schöne, 1975).