LATITUDINAL VARIATION IN THE THERMAL BIOLOGY OF ORNATE BOX TURTLES

We compare the thermoregulatory behavior of ornate box turtles (Terrap ene ornata) from a northern population in Wisconsin with published inf ormation about a southern population in Kansas. In a laboratory therma l gradient, body temperature (T(b)) of Wisconsin turtles (23.5 +/- 1.3 C SE) averaged 6.3 C lower than reported for the same species from Ka nsas. T(b) of free-living turtles in Wisconsin (measured with temperat ure-sensitive transmitters) averaged 4.0 C lower than T(b) of Kansas t urtles when the turtles were basking, moving, or seeking thermal prote ction in burrows from high temperatures. Using field measures of opera tive environmental temperature (T(e); measured with hollow copper mode ls), we deduce (1) that the lower field T(b) of Wisconsin turtles refl ects active selection of lower T(b) and is not simply a passive result of a lower environmental heat load; and (2) that behavioral selection by Wisconsin turtles of a lower and broader range of T(b) increases p otential daily activity time.