Sun-Compass Orientation in the Painted Turtle, Chrysemys picta (Reptilia, Testudines, Testudinidae)

Chrysemys picta, trained for ten days on an E-W axis, exhibited a significant (PS 0.05) unipolar response when tested in an aquatic circular arena. Similarly, when these same animals were tested five days later, they exhibited a highly significant (P< 0.005) orientation in the trained direction. When the turles were subjected to a phase delay of six hours in their photoperiod, their direction of orientation was shifted 90? clockwise. The fact that the turtles compensated for the sun's apparent movement, following light dark (LD) rephasing, indicates the possession of an internal biological clock synchronized by ambient light cycles. This study indicates that Chrysemys picta are able to employ celestial cues, in conjunction with an internal biological clock, for sun-compass orientation. * * *