Flexibility in metabolic rate in a small Afrotropical bird Zosterops virens

Reversible, within-individual variation (flexibility) in phenotypic traits may be influenced by natural selection, and may confer costs and benefits on the individual. Specifically, flexibility in avian basal metabolic rate (BMR) seems to be linked to flexibility in the masses of certain organs and in the metabolic intensities of certain tissues, and depends primarily on body mass, but also on various environmental factors, including thermal acclimation and seasonal acclimatisation. Latitude of origin, captivity and aridity can also affect avian BMR, however authors warn against the use of simple dichotomies (e.g. arid vs. mesic) when analysing results, since various factors are interdependent, and this may complicate analyses. Furthermore, the effect of phylogeny on avian BMR continues to be strongly debated, with differences between passerines and nonpasserines disappearing when phylogenetically informed analytical techniques are employed. Although the fast responses of many species to recent climate change allow for some optimism in the face of predicted climate change scenarios, much of the current knowledge of the effects of climate change on birds is restricted to passerines from northern hemisphere