Microclimates and energetics of free-living box turtles, Terrapene carolina, in South Carolina

We measured microclimate, field metabolic rates (FMRs), water flux, and activity patterns of telemetered box turtles (Terrapene carolina) in South Carolina from September 1987 to October 1988. Turtles were inactive for most of the winter and were active only sporadically during the rest of the year. Using the doubly labeled water method, we found that water flux averaged 8.8, 18.9, and 26.4 mL kg(-1) d(-1) in winter, spring, and summer/fall, respectively. FMR for the same periods averaged 0.028, 0.065, and 0.124 mL CO2 g(-1) h(-1). Differences in FMR among seasons were significant but not between sexes. Using operative temperatures, we predicted standard and maximum metabolic rates of turtles. In winter, FMR was elevated above standard metabolic rates and close to maximum metabolic rates, whereas in spring and summer/fall, FMR fell midway between standard and maximum metabolic rates. We used a model to predict metabolic rates, geographical distribution, and potential reproductive output of box turtles across latitudes in eastern North America. Low FMR and low annual reproductive output may allow box turtles to survive and flourish in unpredictable resource environments by minimizing costs and risks, thereby maintaining greater lifetime reproductive success.