Figure 2.

Species-specific changes in the timing of three phases of spring migration (first 5, 50 and 95% of the spring total) in five species of long-distance migratory birds (lesser whitethroat (triangles), whitethroat (squares), blackcap (circles), chiffchaff (diamonds) and willow warbler (plus symbols)) when passing the Middle East (filled symbols) and northern Europe (empty symbols) analysed for: (a) change in passage (d yr⁻¹; 1984–2004); (b) relationship between passage in the Middle East and African spring NDVI as well as passage in northern Europe and European spring NDVI (days per unit NDVI; 1984–2000: positive values indicate later passage); and (c) relationship between change in migration duration and European spring NDVI (days per unit NDVI; 1984–2000: negative values indicate reduced migration duration). The five slope estimates for each phase of migration are based on separate model fits and are hence independent. (i) Individual estimates. (ii) Mean values, where error bars are 95% confidence intervals based on the summed sampling variances of each species estimate, $(\sum \text{var}(x_i))\times {(1/5)}^2$.