Repeatability and plasticity of minimal and maximal metabolic rates in a wild bird

Many birds that breed in southern Sweden stay year-round, enduring the harsh winter instead of migrating. They experience immense temperature, daylight, and resource fluctuations throughout the year. Their energy budget is split between different needs such as feeding chicks, shivering to staying warm, and the minimum energy needed to maintain vital body functions and the immune system (basal metabolism, or BMR). The ability of free-living birds to adjust their metabolic machinery to match energy demand is well documented in birds in migratory disposition and during winter acclimatization. Therefore, minimal and maximal metabolic rates are plastic traits.
While rapid phenotypic flexibility of metabolic rates in response to fluctuating conditions is well documented, there may also be a genetic component to the shape of individual reaction norms. If there are fitness consequences associated with different metabolic strategies, we can assume that the metabolic phenotype will evolve in response to changing climatic conditions. Little is known about the repeatability of minimal and maximal metabolic rates in free-living birds. As part of an ongoing study of a wild population of blue tits roosting and breeding in nest boxes in Revinge (~20km from Lund), I will characterize birds by their metabolic phenotype. The aim is to collect repeated observations of metabolic rates for the same individuals in different seasons and years. Understanding plasticity and repeatability of fitness-related and temperature-sensitive traits is of utmost importance for predicting the response of temperate resident birds to climate change.