Seasonal changes in temperature and photoperiod are important environmental cues used by small birds to adjust their body mass (Mb) and thermogenesis. However, the relative importance of these cues with respect to seasonal adjustments in Mb and thermogenesis are difficult to distinguish. In particular, the effects of temperature and photoperiod on energy metabolism and thermoregulation are not well known in many passerines. To address this problem, we measured the effects of temperature and photoperiod on Mb, energy intake, resting metabolic rate (RMR), organ mass and physiological and biochemical markers of metabolic activity, in the Chinese bulbul (Pycnonotus sinensis). Groups of Chinese bulbuls were acclimated in a laboratory to the following conditions: (1) warm and long photoperiod (WL; 30°C, 16 light: 8 dark), (2) warm and short photoperiod (WS; 30°C, 8 light: 16 dark), (3) cold and long photoperiod (CL; 10°C, 16 light: 8 dark), and (4) cold and short photoperiod (CS; 10°C, 8 light: 16 dark), for 4 weeks. The results indicate that Chinese bulbuls exhibit adaptive physiological regulations when exposed to different temperatures and photoperiods. Mb, RMR, gross energy intake (GEI) and digestible energy intake (DEI) were higher in cold acclimated than in warm acclimated bulbuls, and in short photoperiod than in long photoperiod. The resultant flexibility in energy intake and RMR allows Chinese bulbuls exposed to different temperatures and photoperiods to adjust their energy balance and thermogenesis accordingly. Cold acclimated birds had heightened State-4 respiration and cytochrome c oxidase (COX) activity in their liver and muscle tissue compared to warm acclimated birds. Changes in state-4 respiration and COX activity in liver and muscle are cellular mechanisms underlying adaptive thermogenesis in bulbuls. Temperature appears to be a primary cue for adjusting energy budget and thermogenic ability in Chinese bulbuls, photoperiod appears to intensify temperature induced changes in energy metabolism and thermoregulation.
- Received July 14, 2016.
- Accepted December 13, 2016.
- © 2017. Published by The Company of Biologists Ltd