Stopover ecology of migratory Sedge Warblers

Migrating Sedge Warblers Acrocephalus schoenobaenus were captured in Eilat, Israel, during their spring and autumn migra-tion. Data on spring and autumn body masses, their interannual variation and the pattern of fuel accumulation were analysed. Body mass and body condition index significantly varied between the years of study in spring but not in autumn. This may be due to birds over-flying the area, but loop migration might also be involved. Sedge Warblers gain mass in Eilat, both in spring and in autumn. Birds in poor initial condition and those stopping over for a longer period gained more body mass faster. In spring, but not in autumn, the progress of the season was another important factor: late birds gained more body mass. The average rate of body mass gain was 0.179g day–1 ± SE = 0.026. This suggests that Eilat is an important staging area for Sedge Warblers in spring and to a smaller extent in autumn. The birds that migrate between their Palaearctic breeding grounds and sub-Saharan winter quarters have to cross a desert belt in north Africa that is wider in the east than in the west. Many of the migrants stop in Israel because it is the last favourable stopover area for them during autumn, before crossing the Sahara on their way to east Africa. In spring, it is one of the first suitable places they encounter after crossing the Sahel, Sahara and Sinai deserts (Frumkin et al. 1995, Shirihai 1996). Eilat is the southernmost point in Israel and plays an important role as a stopover area for many passerine migrants (Safriel 1968, Frumkin et al. 1995, Morgan and Shirihai 1997, Yosef and Tryjanowski 2002a). Migration and, more specifically, stopover ecology of Sedge Warblers (Acrocephalus schoenobaenus) is a sub