Fig. 4. Flight angle with respect to true air speed for barn swallows (open symbols, N=65) and house martins (filled symbols, N=51). The geometric mean regressions for barn swallows (thin line) and house martins (bold line) are shown. The correlation between air speed and flight angle is much higher for barn swallows (r=-0.71) than for house martins (r=-0.44) even when the two highest values of flight angle for barn swallows are excluded.