Seasonal adjustments in body mass and basal thermogenesis in Chinese hwameis (Garrulax canorus): the roles of temperature and photoperiod

For small birds to survive during seasonal acclimatization in temperate zones, regulation of body mass and thermogenesis is crucial. To determine the role of temperature and photoperiod in seasonal changes in body mass and thermogenesis in Chinese hwameis (Garrulax canorus), we compared body mass, basal metabolic rate (BMR), energy intake and cellular metabolic capacity of the tissue (muscle) and/or organs (liver, kidney, heart and small intestine) in seasonally acclimatized and laboratory-acclimated hwameis. A significant seasonal influence on body mass and BMR (which peaked in winter) was found, and these variations were mirrored by exposing the housed birds to cold temperatures or a short photoperiod. The level of dry matter intake, gross energy intake and digestible energy intake was higher during winter, and in housed animals that were exposed to cold temperatures. These results suggest that by increasing energy intake and thermogenesis, Chinese hwameis can overcome winter thermoregulatory challenges. When compared with warm-acclimated birds, cold-acclimated birds displayed higher mass-specific and whole-organ state 4 respiration in the muscle, liver and kidney, and higher mass-specific and whole-organ cytochrome c oxidase activity in the liver. These data demonstrate that cellular thermogenesis partly underpins basal thermoregulation in Chinese hwameis. Cold temperature and short photoperiod can be used as helpful environmental cues during seasonal acclimatization. However, the role of temperature is more significant compared with that of photoperiod in Chinese hwameis; the changes in energy metabolism and thermoregulation induced by temperature appear to be intensified by photoperiod.