The adjustment of avian metabolic rates and water fluxes to desert environments

We tested the hypothesis that birds in arid environments, where primary pro ductivity is low and surface water is scarce, have reduced energy expenditu re and water loss compared with their mesic counterparts. Using both conven tional least squares regression and regression based on phylogenetically in dependent contrasts, we showed that birds from desert habitats have reduced basal and field metabolic rates compared with species from mesic areas. Pr evious work showed that desert birds have reduced rates of total evaporativ e water loss when exposed to moderate environmental temperatures in the lab oratory. We tested whether reduced rates of total evaporative water loss tr anslate into low field water fluxes. Conventional ANCOVA indicated that des ert birds have reduced water fluxes, but an analysis based on phylogenetica lly independent contrasts did not support this finding, despite the wide ar ray of taxonomic affiliations of species in the data set. We conclude that the high ambient temperatures, the low primary productivity, and the water scarcity in desert environments have selected for or resulted in reduced ra tes of energy expenditure and evaporative water loss in birds that live in these dimes.