A combination of temperature-sensitive radiotelemetry and doubly labeled water was used to determine daily activity periods, thermal profiles, water flux rates, and field metabolic rates (FMR) of free-ranging racers (Coluber constrictor) in a temperate mesic habitat during summer. Results were compared to published values on the closely related, ecologically similar coachwhip (Masticophis flagellum). Racers were active from about 0900-1800 h. Most snakes were in positive water balance. Rates of water influx (9.49 ml/d) and efflux (9.13 ml/d) were related to rates of body mass change (mean = 0.35%/d) and were about four times greater than those of Masticophis inhabiting a more xeric habitat. Mean activity temperature (32C), FMR (0.157 ml CO2/g/h), mass-specific daily metabolic energy expenditure (94.5 kJ/kg/d), calculated values of resting metabolism (20.3 kJ/kg/d), and activity metabolism (74.2 kJ/kg/d) in Coluber were all similar to those of Masticophis. We did not detect any relationship between FMR and either distance moved per day, frequency of activity, or body temperature. Water flux rates were greater in females than in males, but we observed no differences between sexes in body temperature or FMR. Compared to intermolt racers, molting racers had higher body temperatures and FMRs (2%, 15%) and lower water fluxes (17%, 25%), but none of these differences was significant. Compared to early in the activity season, racers in late season had lower body temperatures, were less active, and moved less. Water flux and FMR also decreased (13%, 21%), but the differences were not significant.
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