A test of altitude-related variation in aerobic metabolism of Andean birds

Endotherms at high altitude face the combined challenges of cold and hypoxia. Cold increases thermoregulatory costs, and hypoxiamay limit both thermogenesis and aerobic exercise capacity. Consequently, in comparisons between closely related highland and lowland taxa, we might expect to observe consistent differences in basal metabolic rate (BMR), maximal metabolic rate (MMR) and aerobic scope. Broadscale comparative studies of birds reveal no association between BMR and native elevation, and altitude effects on MMR have not been investigated. We tested for altitude-related variation in aerobic metabolism in 10 Andean passerines representing five pairs of closely related species with contrasting elevational ranges. Mass-corrected BMR and MMR were significantly higher in most highland species relative to their lowland counterparts, but there was no uniform elevational trend across all pairs of species. Our results suggest that there is no simple explanation regarding the ecological and physiological causes of elevational variation in aerobic metabolism.

Automated summary

Endotherms at high altitude face challenges of cold and hypoxia, which may impact their aerobic metabolism. Studies on birds show inconsistent effects of altitude on metabolic rates, indicating complex ecological and physiological causes for elevational variation in metabolism.