Seasonal variation in body mass, body temperature and thermogenesis in the Hwamei, Garrulax canorus

The basal thermogenesis of birds is beginning to be viewed as a highly flexible physiological trait influenced by environmental fluctuations, particularly changes in ambient temperature (Ta). Many birds living in regions with seasonal fluctuations in Ta typically respond to cold by increasing their insulation and adjusting their metabolic rate. To understand these metabolic adaptations, body temperature (Tb), metabolic rate (MR), thermal neutral zone (TNZ) and thermal conductance were measured within a range of temperatures from 5 to 40 °C in free-living Hwamei, Garrulax canorus, in both winter and summer. Body mass was 61.2 ± 0.3 g in winter and 55.5 ± 1.0 g in summer, and mean Tb was 41.6 ± 0.1 °C in winter and 42.3 ± 0.1 °C in summer. TNZ was between 28.3 and 35.1 °C in winter and between 28.7 and 33.2 °C in summer. The mean basal metabolic rate (BMR) within TNZ was 203.32 ± 11.81 ml O2 h− 1 in winter and 168.99 ± 6.45 ml O2 h− 1 in summer. Minimum thermal conductance was 3.73 ± 0.09 joules g− 1 h− 1 °C− 1 in winter and 3.26 ± 0.06 joules g− 1 h− 1 °C− 1 in summer. Birds caught in winter had higher body mass, MR, and more variable TNZ than those in summer. The increased winter BMR indicates improved ability to cope with cold and maintenance of a high Tb. These results show that the Hwamei's metabolism is not constant, but exhibits pronounced seasonal phenotypic flexibility associated with maintenance of a high Tb.