Thermoregulation and water requirements in semiarid and montane populations of the least chipmunk, eutamias minimus—II. Water balance

Abstract

Abstract 1. Chipmunks were acclimatized to ad libitum and restricted water consumption regimes (equal rations of 4 and 2 ml/day) at ambient temperatures of 26, 30, and 34°C. 2. Weight loss is greatest in the semiarid population when water consumption is restricted to 4 ml/day, but greatest in the montane population when drinking 2 ml/day. 3. Urine and blood concentrations of animals on restricted water intake are similar in the two populations. The semiarid population reduces evaporative water loss and fecal water content more than does the montane population. Urine osmolarity is significantly higher in both populations when maintained on restricted water intake than on ad libitum water. 4. Hematocrit of the semiarid population is significantly lower than that of the montane population under both water regimes. 5. Evaporative water loss and evaporative heat loss are significantly greater and surface-specific dry heat conductance significantly less in the semiarid population. 6. Metabolism and body temperature measurements at different times of the year suggest a seasonal change in thermoregulatory characteristics of E. minimus.