Fig. 1. Observed equivalent air speed (Vobs), with horizontal standard deviation bars, normalised by dividing by the calculated minimum power speed (Vmp). Squares are for species that flew by flap-gliding, crosses for flapping and circles for bounding. Data from Table 2.
Fig. 3. Wind effect in species that flew by bounding (A), continuous flapping (B) and flap-gliding (C) with reduced major-axis lines. ‘Tail wind’ is the scalar difference between ground speed and air speed. Horizontal dashed lines show the minimum power speed (Vmp) and the minimum gliding speed (Vmin) assuming a maximum lift coefficient of 1.6.
Fig. 4. Because it free-falls during the ballistic phase, a bounding bird has to pull up during the flapping phase, effectively increasing gravity (g) by a factor 1/q, where q is the power fraction (the proportion of time spent flapping).
Fig. 5. Calculated curves for the chaffinch Fringilla coelebs of (A) mechanical power and (B) effective lift:drag ratio (based on metabolic power) for different values of the power fraction (q). These curves have been extended to 25 m s–1 because chaffinches were observed flying at nearly this speed, but the calculation is insecure at such high speeds.
Fig. 6. Observed wingbeat frequencies in the two bounding species plotted against power fraction. Circles and solid lines, starling Sturnus vulgaris; crosses and dashed lines, chaffinch Fringilla coelebs. Curves, predicted wingbeat frequency from equation 10; horizontal lines, predicted wingbeat frequency for a power fraction of 1 (continuous flapping).
Fig. 7. Calculated curves for the chaffinch Fringilla coelebs of mass-specific work in the contractile component of the flight muscles for different values of the power fraction (q). Horizontal dashed lines, estimated upper and lower boundaries for 80 % conversion efficiency of ATP energy into work, assuming an isometric stress of 300 kPa and strain of 0.2.
Fig. 8. Theoretical curve for efficiency of converting ATP energy into work versus stress normalised by dividing by the isometric stress (Pennycuick, 1991). Vertical dashed lines, upper and lower limits of relative stress for a conversion efficiency of 80 % or more of maximum. Top scale, mass-specific work assuming an isometric stress of 300 kPa and strain of 0.2.
