Metabolism during winter in a subtropical hibernating bat, the Formosan leaf-nosed bat (Hipposideros terasensis)

The 60-g subtropical Formosan leaf-nosed bat, Hipposideros terasensis, hibernates in the wild at warm roost (and hence body) temperatures up to 23 degrees C. For small hibernators, torpid metabolic rate is temperature dependent and thus hibernation in warm hibernacula is predicted to be energetically costly. This species, however, rarely feeds during the hibernation season to offset the expected high energetic costs. In this study we used a respirometry system to quantify physiological characteristics of euthermic and torpid H. terasensis in winter. We tested the hypothesis that H. terasensis exhibits metabolic inhibition during torpor. Our results showed that H. terasensis saved 94.6% energy by using torpor at air temperatures of 15 degrees C, compared with its euthermic metabolic rate at that air temperature. Torpor metabolic rate declined with declining air temperature to around 14 degrees C, but then increased at lower air temperatures of 10-14 degrees C. Above 14 degrees C, the slope of -13.0 degrees K +/- 1.4 degrees K between metabolic rates and body temperatures in an Arrhenius plot (or Q(10) = 4.4) suggests that, in addition to direct temperature effects, H. terasensis exhibited metabolic inhibition during torpor. A model used to evaluate energy expenditure of H. terasensis showed that at 20 degrees C and 23 degrees C a 55-g bat needs 194 kJ (4.9 g fat) and 273.2 kJ (6.9 g fat), respectively, to survive a 70-day hibernation period.