Fig. 6. Distribution of the absolute error between 30min estimates of oxygen consumption rate _O2 and measured _O2 for the six calibrations obtained using the general linear regression model (model i, grey line) when using a combination of resting oxygen pulse (ROP) and the linear regression for the birds walking on the treadmill (model ii, broken line) or when ROPs and active oxygen pulses (AOPs) are expressed as function of the nutritional index (model iii, black line). The horizontal dashed line is the line of 75% of the total errors of 30min estimates, and the arrows indicate the respective error for each model (75% of errors are below 34% when using model i, below 26% when using model ii and below 20% when using model iii).