Intra- and Interspecific Differences in Phototactic Behaviour of Freshwater Turtles

With fresh water turtles Pseudemys scripta elegans some individuals choose a white compartment and others a black one when tested in identical conditions on a small diving stand. These differences could not be related to weight, sex, adaptation to laboratory conditions, or level of illumination in the starting area. Latencies were very variable but for many individual animals responses made to the black side tended to be quicker than those to the white side. Other species (Pseudemys floridana and Pseudemys scripta ornata) showed a higher level of positive phototaxis and less individual variation. In many animals tested the positive response to the white stimulus became more frequent as testing was extended up to 60 trials. Some cautions are given about the design of experiments on learning in turtles. The role of positive phototaxis in the water-finding abilities of hatchling turtles is discussed. The possible value of the study of the negatively phototactic turtles in elucidating some aspects of their life cycle is suggested, but the present work produced no good evidence that individual variations depended on maturational differences.