Time ‘inefficiency’ threshold, beyond which the calories expended by a polar bear to chase an adult female goose exceed the calories obtained from consuming it, as a function of speed of the chase and polar bear mass. Note that projections for speeds >7.9 km/h (dashed vertical line) are extrapolations beyond the available data and should be interpreted with caution, but are pictured for comparison with extrapolations by previous studies. The inefficiency threshold (I) is calculated as follows: I = 667.4/(V˙O2 * mass * 4.735)/60, where 667.4 is the caloric value of a goose, mass-specific oxygen consumption (V˙O2) is estimated as in the legend to Fig. 2, and 4.735 is the standard conversion of 1 litre of oxygen to kilocalories.