PERIODIC AROUSALS IN HIBERNATING MAMMALS - IS EVAPORATIVE WATER-LOSS INVOLVED

1. Using existing data on the rate of cutaneous and pulmonary evaporat ive water loss (EWL) for hibernating Little Brown Bats (Myotis lucifug us) and on the duration of torpor bouts, body temperature (T-b) and ox ygen uptake (V-o2) of Golden-mantled Ground Squirrels (Spermophilus sa turatus), the rate of EWL, was modelled for ground squirrels hibernati ng at ambient temperatures (T-a) of -2, 2, 4 and 8 degrees C. 2. Total EWL showed a curvilinear response to T-a, being lowest at 2 degrees C and increasing with both increasing and decreasing T-a. EWL at -2 deg rees C was about equal to that at 4 degrees C. The duration of torpor bouts showed the same curvilinear response to T-a and torpor bout dura tion at -2 degrees C was similar to that at 4 degrees C (8.5 vs 8.3 da ys, respectively). 3. At T-a greater than or equal to 2 degrees C, whe re T-b of torpid S. saturatus is not metabolically defended, torpor bo ut duration is significantly related to T-b, V-o2 and EWL, with the th ree variables having similar r(2) values. 4. Using the regression equa tions generated at T-a greater than or equal to 2 degrees C to predict torpor bout durations at -2 degrees C, where T-b is metabolically def ended, shows that the three variables do not have equivalent predictiv e abilities. T-b and V-o2 predicted torpor bout durations of 15.2 and -40.4 days, respectively, compared with observed durations of 8.5 days at -2 degrees C. EWL predicted torpor bout durations of 8.4 days or o nly 0.1 days less than that observed at -2 degrees C. 5. The relation between torpor bout duration and total EWL was insensitive to major va riations in cutaneous EWL. Over T-a ranging from -2 degrees C to 8 deg rees C, a stepwise multiple regression including T-b, V-o2 and EWL as independent variables identified EWL as the only variable significantl y correlated with torpor bout duration. 6. Our analyses suggest that t orpor bout duration may be influenced by EWL, indicating that animals may need to obtain free water when they arouse. An analysis of the str uctural and temperature characteristics of ground squirrel hibernacula suggests that they may function as a biological condensing tower. Thr oughout winter, water should evaporate from the warm lower levels and condense in the colder upper regions and so free water may be availabl e to animals when they arouse.