Energetics of free-ranging mammals, reptiles, and birds

We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique . Allometric (scaling) relationships are calculated for mammals (79 species ), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expend iture and daily food requirements of free-ranging mammals, reptiles, and bi rds. Significant scaling differences between various taxa, dietary, and hab itat groups (detected by analysis of covariance with P 0.05) include the fo llowing: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mam mals (0.590); (c) among families of birds, slopes do not differ but elevati ons (intercepts) do, with passerine and procellariid birds having relativel y high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizar ds have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) car nivorous mammals have a relatively high slope and carnivorous, insectivorou s, and nectarivorous birds have relatively higher FMRs than do omnivores an d granivores. The difference detected between passerine and nonpasserine bi rds reported in earlier reviews is not evident in the larger data set analy zed here. When the results are adjusted for phylogenetic effects using inde pendent contrasts analysis, the difference between allometric slopes for ma rsupials and eutherians is no longer significant and the slope difference b etween Scleroglossan and Iguanian lizards disappears as well, but other tax onomic differences remain significant. Possible causes of the unexplained v ariations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terre strial vertebrates that remain under- or unstudied and such factors as repr oductive, thermoregulatory, social, and predator-avoidance behavior.