Fig. 2. Metabolic power measured using doubly labelled water (P_met,DLW) in relation to the flight speed (V) of four starlings during flight in a wind tunnel. The different symbols show data from different birds (diamonds, bird 2, N=7; triangles, bird 12, N=7; circles, bird 15, N=9; squares, bird 19, N=7). The line describes the overall relationship: P_met,DLW =135.9±23.9V^–1+0.0047±0.0012V³–8.47±4.72.Due to the scatter in the data, it is not possible to place any emphasis on the individual data points. Instead, we use a line calculated from the average coefficients across birds to describe the central trend in the data. The coefficients and minimum power speed of this line are only approximate.