48.4 Thursday, Jan. 5 Do body composition drives winter variations of metabolic performance in black-capped chickadees (Poecile atricapillus)? PETIT, M*; VEZINA, F; Université du Québec à Rimouski; Université du Québec à Rimouski Magali.Petit@uqar.qc.ca
Throughout the year, resident birds species living at northern latitudes exhibit changes in metabolic performance in response to seasonal variation in climatic conditions. Indeed, basal metabolic rate (BMR, reflecting minimal maintenance energy costs) and maximal thermogenic capacity (Msum, a measure of cold tolerance) are typically higher in winter relative to other seasons. BMR variations are commonly seen as reflecting the energy consumption of internal organs remaining active at rest whereas Msum, because it is the product of shivering activity, is thought to depend on muscle size. However, few studies investigated intraseasonal variations in metabolic performance and the role of organ size flexibility in this variation is unknown. Using black-capped chickadees as our model species, we measured daily variations in BMR and Msum within winter (November 2010 to March 2011). We also collected 20 birds of known metabolic performance in the beginning of winter (November), peak of cold (February) and at the end of winter (March) to study intraseasonal variations in organ size and its effect on metabolic parameters. Preliminary results show an increase in metabolic performance peaking in February and remaining high throughout the rest of winter, with a high level of variability likely reflecting daily changes in weather. These findings will be discussed in light of the observed variations in body composition.