Fig. 3

Visual representation of the flight directions and speeds of soaring migrants together with the wind conditions. Panel A shows the lateral component of airspeed (LcA) on the y-axis and its change throughout the day, with overlapped vectors of mean groundspeed (red), airspeed (green) and wind speed (blue). Note that partially transparent values indicate the variation for each hour including data from each day of tracking from all the 7 years used in this study (2005–07, 2009, 2014–16). For visual purposes the vectors are not in scale, see the legend to contextualize the vector magnitude. Dashed grey line with intercept y = 0 shows the full compensation line, where the groundspeed vectors align with the goal direction (187.7°). Panel B shows circular histograms of wind directions (blue) and soaring bird flight directions (red), the arrows represent the mean directions following Rayleigh tests (in which 0 = “uniform distribution” and 1 = “all the data are in the same direction”), which for the track birds is r = 0.99 (p < 0.0001) and for the winds is r = 0.90 (p < 0.0001)