Kulaszewicz I. & Jakubas D. (2015) Factors affecting post-breeding moult in the Savi’s Warbler Locustella luscinioides in northern Poland. ARDEA 103 (1): 61-68

A majority of Eurasian short-distance migrants moult after breeding and before autumn migration, while most long-distance migrants perform a winter moult in the tropics after autumn migration. Another strategy among long-distance migrants is a partial moult on the breeding grounds, suspended moult and then completion of moult on the wintering grounds. The Savi’s Warbler Locustella luscinioides is a small passerine adopting such a ‘suspended moulting’ strategy. Here, we investigate the sequence and extent of the post-breeding moult in Savi’s Warblers breeding in and migrating through northern Poland in relation to sex, body mass and date. We analysed 65 molecularly sexed adult Savi’s Warblers (32 females and 33 males) caught during autumn migration in 2010– 2011. Adult Savi’s Warblers from the studied populations were found to suspend moult. Exchange of wing feathers started at the third primary (P3) and progressed in both directions. The onset of secondary moult began with S1 and occurred when P6 was shed. Tail moult occurred almost simultaneously with the secondaries. We did not find any significant differences between the sexes in time and extent of moult. Lack of sex differences in the time of moulting suggests comparable post-breeding condition (fat load, body mass) of females and males. In contrast to the present study, adults caught in Western Europe started post-breeding moult from P5, which may be explained by different populations migrating through northern Poland and Western Europe.