SREL Reprint #2067
Rates of Metabolism and Water Flux in
Free-Ranging Racers,
Coluber constrictor
MICHAEL V. PLUMMER AND JUSTIN D. CONGDON
Abstract:
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 ftee-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 C02/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.
SREL Reprint#2067
Plummer, M.V. and J.D. Congdon. 1996. Rates of metabolism and water flux in free-ranging racers, Coluber constrictor. Copeia 1996:8-14.
