Phylogenetic Analysis of Avian Energetics: Passerines and Nonpasserines Do Not Differ

We reevaluated comparative data on avian metabolic rates, using two recently developed statistical techniques for analysis of phylogenetically dependent data: Felsenstein's method of independent contrasts and Monte Carlo simulation. Contrary to the results of previous studies, our results found no significant differences in basal metabolic rate between passerine and nonpasserine species, once both phylogeny and body mass effects are accounted for. The common assumption that species from "extreme" groups (such as ratites, columbids, and shorebirds) differ energetically from other, "conventional" birds was not supported by our analyses. Because empirically based allometric relationships are critically dependent on the underlying assumptions of the statistical model, so-called adaptive explanations of observed departures from expectation should be corroborated by experimental data and alternative evolutionary models.