Figure 3

Ground speed during the post-breeding migration over barriers (a) desert and (b) sea, and (c) non-barriers and during the pre-breeding migration over barriers (d) desert, (e) sea, and (f) non-barriers. Only travel segments for each hour of the day are included. The grey areas in the background indicate nocturnal hours, and the white area indicates diurnal hours. Points represent outliers. Speed patterns are more similar when flying over the desert and non-barriers than over the sea, although over the desert, speeds are higher during the post-breeding migration, likely due to supportive winds (see Fig. 4). Over the sea kestrels achieve more constant travel speeds between ~ 25 and 50 km/h with no differences between diurnal and nocturnal flights. During diurnal travel over non-barriers travel speed typically falls below 25 km/h.