Fig. 1. Resting (basal) metabolic rates (RMR; log_eRMR in kJ day^-1) of 639 mammals (A) and 381 birds (D) as a function of body mass (M_b, in g). [Least-squares fit equations: mammals, log_eBMR=0.781+0.677log_eM_b, F=6605.89, P<0.001, r²=0.915, RMA gradient=0.708; birds, log_eBMR=1.224+0.671log_eM_b, F=8574.1, P<0.001, r²=0.958, RMA gradient=0.685.] Lifespans (years) of 249 mammals (B) and 164 birds (E) as a function of body mass. [Least-squares fit equations: mammals, log_elifespan=0.85+0.209log_eM_b, F=157.66, P<0.001, r²=0.390, RMA gradient=0.334; birds, log_elifespan=1.514+0.216log_eM_b, F=134.12, P<0.001, r²=0.458, RMA gradient=0.319] and lifetime expenditure of basal energy per gram of body tissue (kJ g^-1 life^-1) plotted against M_b (g) for 240 mammals - excluding 9 bat species (C) and 141 birds (F) [least-squares fit equations: mammals, log_e(lifetime expenditure per gram)=7.268-0.0734log_eM_b, F=17.97, P<0.001, r²=0.07, RMA gradient=-0.278; birds, log_e(lifetime expenditure per gram)= 8.635-0.109log_eM_b, F=23.28, P<0.001, r²=0.126, RMA gradient= -0.307].