Fig. 4. Observed ground speeds (Vg, m s-1) and
observed air speeds (Va, m s-1) during flapping
(+) and soaring (
) flight for the black-headed gull (A) and the lesser
black-backed gull (B). Regression lines are shown for each species and each
flight strategy (solid line for soaring, broken line for flapping; the 1:1
line is included for reference purposes). The frequency distributions of
Va and Vg during soaring and flapping
flight are presented along the respective axes at the right and top. The lines
of the frequency distributions are shifted slightly along the category axis
for display purposes.