These large turtles selected a narrow range of microhabitats that were significantly warmer and less variable in temperature than random sites.

We tested the hypothesis that alligator snapping turtles ( Macroclemmys temminckii) selected microhabitats based on temperature by comparing temperatures at sites used by turtles to temperatures at randomly selected sites. The interactions among body size, physiology, and behavior on the thermal biology of large, entirely aquatic, ectotherms is poorly understood. Yet, even in water, individuals may exert control over body temperature ( T b) via behaviors such as selecting thermally favorable microhabitats. The variations between core T b, cloacal T b and other measures of T b indicated that there are large thermal gradients within the body of a relatively large tortoise at any given time with cloacal T b not an accurate measure of core T b.Įctotherms in water experience rates of heat transfer at least two orders of magnitude greater than in air, seriously constraining their thermoregulatory capabilities. In addition, significant differences were found between measures of temperature from other parts of the body. Cloacal T b's were significantly lower than all other body temperatures measured, and core T b's were significantly different from cloacal T b, skin and carapace temperatures. Measurements of temperature from various positions on and in the tortoise were significantly different from T a. Temperatures were measured from various positions on leopard tortoises ( Stigmochelys pardalis) using thermocouples and miniature temperature loggers, including surgically implanted temperature loggers. We expected that there was a difference between skin, cloacal, and core T b's. The advent of surgically implanted miniature temperature loggers has offered the opportunity to test the efficacy of cloacal T b as a measurement in thermoregulatory studies. Historically, studies of reptilian thermal biology have compared ambient temperatures ( T a) to body temperatures ( T b) from the animal under study, with T b usually taken from the cloaca and various instruments being used to measure T b.

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