Metabolism and Thermoregulation in Waxwings (Bombycilla garrulous) and Black-faced Buntings (Emberiza spodocephala)

In order to understand the ecophysiological characteristics of the waxwing (Bombycilla garrulous) and black-faced bunting (Emberiza spodocephala) inhabiting in relative cold area,we measured their metabolic rates (MR),body temperatures (Tb),and thermal conductance ? at temperature range of 5,10,15,16,18,20,22,25,26,28 and 30 ℃. Adult waxwings and buntings were live-trapped by mist net in the Qiqihar City,Heihongjiang Province (47°29′N,124°02′E) from April to July 2004. Eight waxwings (seven males and one female) and eight buntings (all males) were used in this experiment. Body masses to the nearest 0.1 g were determined immediately upon capture with a Sartorius balance (model BT25S). The mean body mass of waxwings and buntings were 64.9±0.6 g and 15.1±0.2 g (mean±SE),respectively. Birds were transported to the laboratory and caged (50×30×20 cm3) under natural photoperiod and temperature. Food and water were supplied ad lib. MR was measured by using closed circuit respirometer,and temperature was controlled by water bath (±0.5 ℃),Tb was measured by insertion of a digital thermometer (Beijing Normal University Instruments Co.) into the cloaca,and C was calculated at each temperature below the thermal neutral zone using the formula:C=MR/(Tb-Ta),where Ta is ambient temperature. The thermal neutral zone of waxwings and buntings were 18-27 ℃ and 20-26 ℃,respectively. The mean metabolic rates within thermal neutral zone of these species were 2.33±0.47 and 4.75±0.18 mL O.2/(g·h),respectively,which are 110% and 151% of the expected value from their body mass,respectively. Mean Tbs of waxwings and buntings were 38.20±0.05 and 38.25±0.05 ℃,respectively. Conductances of waxwings and buntings were 0.13±0.00 and 0.26±0.00 mL O.2／(g·h·℃),respectively,representing 153% and 157% of the expected value based on their body mass. Below the lower critical temperatures MR increased with declining Ta and the regression equations relating MR to Ta was described as:MR=5.46(±0.19)-0.17(±0.01) Ta for waxwings and MR=9.54(±0.52)-0.23(±0.03) Ta for black-faced buntings,respectively. The ecophysiological characteristics of these species are: high body temperature and metabolic rate,wide thermal neutral zone and lower critical temperature and relatively high thermal conductance. These properties might make them acclimatized to their environments and survive at relative cold areas for these species.