Fig. 5. Graphical representation of the three different models used to estimate the rate of oxygen consumption _O2 from heart rate fH in a hypothetical arriving male with a bill length of 123.8mm and a body mass of 12.2kg (nutritional index NI=3.2). The grey line represents the general linear regression model (GLR) for departing males, the broken lines use a combination of resting oxygen pulse (ROP) (from minimum resting fH, , to maximum resting fH, R) and the linear regression for the birds walking on the treadmill (from minimum exercising fH, , to maximum walking fH, ). The solid black lines represent the model using ROPs and active oxygen pulses (AOPs) as function of the nutritional index (NI).