Stopover Duration and Body Mass Change of Two Siberian Songbird Species at a Refuelling Site in the Russian Far East

Abstract Long-distance bird migration is often characterized by a number of flight bouts interspersed with intermittent stopover periods for re-fuelling. However, little is known about the stopover ecology of songbirds migrating along the East Asian flyway. The aim of this study was to estimate the minimum stopover duration and body mass change during stopover of Red-flanked Bluetail Tarsiger cyanurus and Yellow-browed Warbler Phylloscopus inornatus based on 6,073 ringed and 502 re-captured birds during spring and autumn migration in the Russian Far East. For Red-flanked Bluetail the minimum stopover duration averaged 3.4 days in autumn and 1.7 days in spring, while for Yellow-browed Warbler it was 3.2 days in autumn and 2.1 days in spring. Significant differences in stopover duration were found between seasons, but not between the two species. The body mass of Red-flanked Bluetails significantly increased during stopover in spring and autumn, but no significant body mass changes were detected in Yellow-browed Warblers. The shorter minimum stopover duration of both species in spring may indicate a faster migration than in autumn, suggesting a time-minimizing strategy in spring to reach the breeding grounds as fast as possible.