Fig. 7. The mean rate of change in heading during a stroke was closely related to the roll angle measured at mid-downstroke. Individual points are the average response of a bird for a given wingbeat number and turn direction; N=59. Although the regression line and equation represent a simple linear regression between the two measurements, the r² and P values reflect the partial correlation between the two variables, controlling for the temporal non-independence of roll angle as described in Materials and methods. The r² for the simple linear regression was 0.953 with P<0.00001 and F=1264.