Long-term repeatability of winter basal metabolic rate and mass in a wild passerine

P>Basal metabolic rate (BMR) is an important trait in the study of energy management of an individual, especially in small wintering passerines from the north which have one of the highest energy turnover rates in vertebrates. Laboratory studies have shown the trait to be repeatable and heritable, despite its plastic nature. However there is currently a lack of empirical data from wild passerine populations. We studied within- and between-year repeatability of BMR, body mass and mass-independent BMR from two populations of wintering great tits (Parus major) at the northern range of their distribution. We found body mass, BMR and mass-independent BMR to be highly repeatable both within and between years. Our results provide the first evidence from a wild small passerine that, despite a large environmentally induced variation in metabolic rate, individuals show consistent metabolic strategies over periods even longer than a year. Homeotherm species exposed to new or changing environmental conditions may be able to evolve specific energetic strategies in the wild, as previously found in captive species.