Statistical significance of oxygen consumption and ATP synthesis changes induced by ADP was assessed using two-way analysis of variance (ANOVA) with ADP and penguins or temperature as the main factors. Mitochondrial apparent Km for ADP were determined for both oxygen consumption and ATP production by fitting experimental data by the Michaelis–Menten equation: V=(Vmax×[ADP]) / (Km + [ADP]) using sigma plot 12.0 software. Mitochondrial and kinetic parameters were tested with one-way ANOVA for independent (effect of nutritional status) or repeated (effect of temperature) values followed by protected least significant difference tests or paired Student's t-tests (Statview v.4.5 software). Data are presented as means±s.e.m. with significance considered at P<0.05.