Fig. 1. Time course of (A) the rates of oxygen consumption () and carbon dioxide production (), (B) metabolic power and (C) respiratory exchange ratio during a wind tunnel flight by starling 15 at 13.3 m s^–1. Error bars show the standard error of four measurements made each minute (each of which was the mean value over 15 s). The printed symbols are larger than the error bars during most minutes. The bird flew for 12 min, starting at time 0. Metabolic rate increased when the bird was placed into the flight chamber immediately after the mask had been attached and when the bird was caught to remove the mask at the end of the measurement.