Thermal Relations of Hibernating Painted Turtles, Chrysemys picta

Abstract

Reports that hibernating Chrysemys picta have body temperatures a few degrees warmer than the ambient mud and water temperatures were investigated by quantifying the thermal relations of turtles hibernating under simulated natural conditions. The deep body temperatures of eight hibernating Chrysemys were never higher or lower than environmental temperatures. Similar results were obtained from a dead control turtle. Therefore hibernating turtles do not exhibit endothermy or physiological temperature control. However, analysis of regression slopes of body temperature on environmental tem- peratures suggests the possibility of behavioral temperature control by exploiting a mud/water thermal gradient. Body temperatures of ectotherms in a heterogeneous thermal environment in the absence of solar radiation are composites of environmental temperatures. Chrysemys picta has the northernmost range of any North American turtle (Carr, 1952). Northern populations are exposed to ambient temperatures lower than 10?C for up to six months of the year, and they are known to spend the winter in a state of hibernation (brumation) buried in the mud of pond bottoms. Ernst (1972) report- ed that the cloacal temperatures of adult C. picta hibernating in natural ponds were elevated above ambient mud and water temperatures. Ernst and other workers have suggested on the basis of laboratory experiments that turtles may be capable of maintaining body temperatures elevated 0.3-5.5?C above low ambient temperatures by endogenous heat production (Baldwin, 1925; Edgren and Edgren, 1955; Ernst, 1972). This study investigated this phe- nomenon under simulated natural condi- tions.