Fig. 4. Relationship between mechanical power output of (A) zebra finch and (B) budgerigar pectoralis muscle fascicles and simulated flight speed. Open circles show the power output of supramaximally stimulated muscle measured in vitro. Open triangles show these values corrected to account for in vivo changes in EMG intensity with flight speed. Closed triangles show the values from supramaximally stimulated muscle corrected to account for changes in EMG intensity and the relative duration of non-flapping flight with flight speed. For each species and within each set of conditions (in vitro, estimated in vivo and flight power), mean values designated by the same number were not significantly different (Scheffé P>0.05). Values are means ± s.e.m. (budgerigars: N=11, 9, 9, 6, 9, 5, 7 for speeds 4, 6, 8, 10, 12, 14, 16 m s^–1, respectively; zebra finches: N=7, 6, 3, 5, 4, 4, 7 for speeds 0, 4, 6, 8, 10, 12, 14 m s^–1, respectively).