Climate in Both Hemispheres Shapes the Interannual Variation in the Timing of the Southward Migration of the Spotted Flycatcher <em>Muscicapa striata </em>from the Baltic Region to South Africa

The Spotted Flycatcher is a long-distance migrant insectivore, breeding in western Eurasia and migrating to Africa south of the Sahara. This paper focuses on the annual variation of its southward post-breeding migration. It uses two monitoring datasets: bird ringing data of on passage through Bukowo-Kopań (Baltic Sea coast, N Poland), (14 August–1 November in 1967–2025); and bird atlas data from the Second Southern African Bird Atlas Project (2007–2025) between 24°–26°S and 27°–29°E, on the south of the species’ non-breeding range. For each dataset, we computed the annual anomaly as the area between the multi-year average cumulative curve and the annual curve of migration. The number of birds ringed per 50 mistnets was an index of migrants’ abundance each year. For the atlas data, we calculated an index of peak abundance at the end of arrivals. These four measures of migration were response variables, and indices of climate in Europe and Africa were explanatory variables in multiple regression models. The best models showed that the East-Atlantic/Western Russia oscillation in May–July was related to Spotted Flycatchers’ migration at Bukowo–Kopań and South Africa. May–September temperatures around the Baltic contributed to explaining interannual variation in passage at Bukowo-Kopań. October–November temperatures south of Sahel largely explained variation in arrivals in South Africa; these results are less robust due to 18 years available. We showed that climate at the breeding grounds and on route have combined carry-over effects on migrants, manifested similarly at distant locations along flyways.