Nonconformance of standard metabolic rate with body mass in Hawaiian Honeycreepers

Summary

Among four species of Hawaiian Honeycreepers, three from Hawaii (Vestiaria coccinea, 15.0 g; Himatione sanguinea, 12.9 g; Loxops virens, 10.7 g) and one from Kauai (Loxops parva, 7.9 g), standard metabolic rate (in ml O₂/g·h) was positively related to body mass, the opposite of that predicted by conventional endothermic allometry. SMR of V. coccinea conformed to the predicted value, but in the remaining species was progressively reduced below expected levels as body mass decreased. All four species occur predominantly in Metrosideros collina forests, where their preferred food is the nectar of its blooms. At least on Hawaii and during periods of moderate bloom the species are aligned along a dominance hierarchy, with the largest species most dominant and most successful at nectar exploitation. I believe that nonconformancy of SMR with body mass in the smaller species reflects an energy-conserving measure, the degree of which is dictated by social position and relative success in nectar exploitation.