Figure 5

Departure time of radio-tracked songbirds in relation to the length of the night. Blue = autumn, orange = spring migration. Blue circle: northern wheatears from Wales, Alaska, in autumn (this study); orange square edged black: northern wheatears of the oenanthe subspecies passing Helgoland, Germany, in spring [15]; orange triangle edged black: northern wheatears of the leucorhoa subspecies passing Helgoland, Germany, in spring [14]; orange ring: sedge warbler passing Rybachy, Russia, in spring [18]; blue diamond: reed warblers passing Falsterbo, Sweden, in autumn [17]; blue and orange crosses: Eurasian robins passing Rybachy Russia [16]. Northern wheatears at Wales did not set off at a lower proportion of night than sedge warblers in Rybachy (Wilcoxon test: W = 61, P = 0.11), but it differed in general significantly between the considered species (GLM with binomial error distribution: P < 0.0001, Additional file 9).