Heart rate as an indicator of oxygen consumption: Influence of body condition in the king penguin

The use of heart rate to estimate field metabolic rate has become a more wi dely used technique. However, this method also has some limitations, among which is the possible impact that several variables such as sex, body condi tion (i.e. body fat stores) and/or inactivity might have on the relationshi p between heart rate and rate of oxygen consumption. In the present study, we investigate the extent to which body condition can affect the use of hea rt rate as an indicator of the rate of oxygen consumption. Twenty-two breeding king penguins (Aptenodytes patagonicus) were exercised on a variable-speed treadmill. These birds were allocated to four groups ac cording to their sex and whether or not they had been fasting, Linear regre ssion equations were used to describe the relationship between heart rate a nd the rate of oxygen consumption for each group. There were significant di fferences between the regression equations for the four groups. Good relationships were obtained between resting and active oxygen pulses a nd an index of the body condition of the birds. Validation experiments on s ix courting king penguins showed that the use of a combination of resting o xygen pulse and active oxygen pulse gave the best estimate of the rate of o xygen consumption (V) over dot(O2). The mean percentage error between predi cted and measured (V) over dot(O2) was only +0.81% for the six birds. We conclude that heart rate can be used to estimate rate of oxygen consumpt ion in free-ranging king penguins even over a small time scale (30min), How ever, (i) the type of activity of the bird must be known and (ii) the body condition of the bird must be accurately determined. More investigations on the impact of fasting and/or inactivity on this relationship are required to refine these estimates further.