Environmental and ecological correlates of avian field metabolic rate and water flux

1. The field metabolic rate (FMR) of an endothermic animal represents its energy expenditure in a natural environment, or its energy budget, and its field water flux (FWF) reflects the animal’s water requirements.
2. We examined FMR of 103 species and FWF of 75 species of adult birds from direct field measurements by the doubly-labelled water method, and used the phylogenetic generalised least squares method to conduct a phylogenetically-informed, comprehensive analysis of the relationship between FMR, FWF, and multiple environmental and biological variables.
3. FMR was strongly positively associated with body mass with an allometric exponent of 0.66, and seabirds had lower FMR than terrestrial species. Birds consuming plant matter had lower FMR compared to omnivores, carnivores or nectarivores, and low ambient temperature was associated with higher FMR. There was little evidence for phylogenetic covariance in FMR, even though previous studies identified a phylogenetic signal for BMR....