Metabolic thermogenesis and evaporative water loss in the Hwamei Garrulax canorus

Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (T-b), metabolic rate (MR) and EWL at ambient temperatures (T-a) between 5 and 40 degrees C. Overall, we found that mean body temperature was 42.4 degrees C and average minimum thermal conductance (C) was 0.15 ml O-2 g(-1) h(-1) degrees C-1 measured between 5 and 20 degrees C. The thermal neutral zone (TNZ) was 31.8-35.3 degrees C and BMR was 181.83 ml O-2 h(-1). Below the lower critical temperature, MR increased linearly with decreasing Ta according to the relationship: MR (ml O-2 h(-1)) = 266.59-2.66 T-a. At T(a)s above the upper critical temperature, MR increased with Ta according to the relationship: MR (ml O-2 h(-1))= 271.26+12.85 T-a. EWL increased with T-a according to the relationship: EWL (mg H2O h(-1))= 19.16+12.64 T-a and exceeded metabolic water production at T-a > 14.0 degrees C. The high T-b and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures. (C) 2013 Published by Elsevier Ltd.