Body temperature is a repeatable trait in a free-ranging passerine bird

Body temperature (Tb) affects animal function through its influence on rates of biochemical and biophysical reactions, the molecular structures of proteins and tissues, metabolic rate, and ultimately, organismal performance. Despite its importance in driving physiological processes, there are few data on how much variation in Tb exists within populations of organisms, and whether this variation consistently differs among individuals over time (i.e., repeatability of a trait). Understanding the repeatability of Tb is important for predicting how animal populations will respond to climatic warming, given that endotherms maintain Tb that are close to the upper lethal threshold.  Here, we quantified the repeatability of Tb, both in the context of a fixed average environment (~21°C) environment and across ambient temperatures, in a free-living population of tree swallows (Tachycineta bicolor). by experimentally trimming the ventral plumage of a subset of female swallows, we also asked whethe...