Fig. 7. The estimated normal probability distribution of air speeds (V_a, m s^-1) during flapping (broken line) and soaring flight (solid line) for the black-headed gulls (A) and lesser black-backed gulls (B). This simplification of the data can be used to predict, for example, the range of V_a where the soar/flap ratio is <1 (area shaded in gray). Thick solid lines at the top of each figure represent alternative selection criteria that can be used to determine the soar/flap ratio <1 (area shaded in gray): for example, where R_diff<1.9 W and R_s>11.6 (black-headed gull).