Figure 4.

The relationship between flight and wind conditions, for all flight bursts for which wind data were available (n = 189). (a) Relationship between wind speed and burst power variance, with flap-like bursts shown in black and soar-like bursts in white. (b) Histogram of the per-burst difference in degrees between the bird's flight direction (beeline bearing) and wind direction, where a value of 0° denotes no difference (i.e. flight direction is the same as wind direction). For modelling, flight direction was categorized as headwind (shown in red), crosswind (grey) or tailwind (blue). (c) Wind speed is a highly significant predictor of soar-like flight (logistic mixed-effects regression controlling for individual and day), with soaring less likely to occur in strong headwind than tailwind or crosswind. Grey histograms show density of wind speeds for all bursts classified as either flap-like (bottom) or soar-like (top).