Background The arrival of many species of migrant passerine in the European spring has shifted earlier over recent decades, attributed to climate change and rising temperatures in Europe and west Africa. Few studies have shown the effects of climate change in both hemispheres though many long-distance migrants use wintering grounds which span Africa. The migrants’ arrival in Europe thus potentially reflects a combination of the conditions they experience across Africa. We examine if the timing of spring migration of a long-distance migrant, the Willow Warbler, is related to large-scale climate indices across Africa and Europe. Methods Using data from daily mistnetting from 1 April to 15 May in 1982–2017 at Bukowo (Poland, Baltic Sea coast), we developed an Annual Anomaly metric (AA, in days) to estimate how early or late Willow Warblers arrive each spring in relation to their multi-year average pattern. The Willow Warblers’ spring passage advanced by 5.4 days over the 36 years. We modelled AA using 14 potential explanatory variables in multiple regression models. The variables were the calendar year and 13 large-scale indices of climate in Africa and Europe averaged over biologically meaningful periods of two to four months during the year before spring migration. Results The best model explained 59% of the variation in AA with seven variables: Northern Atlantic Oscillation (two periods), Indian Ocean Dipole, Southern Oscillation Index, Sahel Precipitation Anomaly, Scandinavian Index and local mean temperatures. The study also confirmed that a long-term trend for Willow Warblers to arrive earlier in spring continued up to 2017. Discussion Our results suggest that the timing of Willow Warbler spring migration at the Baltic Sea coast is related to a summation of the ecological conditions they had encountered over the previous year during breeding, migration south, wintering in Africa and migration north. We suggest these large-scale climate indices reflect ecological drivers for phenological changes in species with complex migration patterns and discuss the ways in which each of the seven climate indices could be related to spring migration at the Baltic Sea coast.

Extended primary moult as an adaptation of adult Wood Sandpipers Tringa glareola to their freshwater habitats in southern Africa. Ardea 97(3): 271-280.Migrant waders using freshwater habitats are hypothesized to have slower primary moult than waders using coastal habitats. We chose the Wood Sandpiper Tringa glareola as a representative species using the freshwater habitats and compare its moult pattern with a range of fresh-water and coastal wader species to test the habitat hypothesis. Only fragmentary descriptions of Wood Sandpipers' primary moult in their sub-Saharan non-breeding quarters had existed. We analysed the primary moult formulae of 1496 adult Wood Sandpipers obtained in southern Africa. The Underhill & Zucchini moult model was used to estimate the timing and duration of moult for all 10 primaries combined and for each primary individually. We also estimated the rate of production of feather material during moult. Adult Wood Sandpipers arrive in southern Africa between late July and November, and depart from mid-March to April. Suspension of moult was observed in 56 birds (7.5%) after two to nine primaries had been replaced. The remaining birds performed a continuous complete primary moult, with average start and completion dates of 21 August and 30 December, respectively; estimated duration was 131 days. The overall rate of production of primary feather material was uniform, achieved by growing up to five small inner primaries simultaneously at the beginning of the moult but only one or two simultaneously while the large outer primaries were growing. Primary moult of adult Wood Sandpipers took longer but ended earlier than in similar-sized waders using coastal habitats. Compared with waders using coastal habitats, Wood Sandpipers prolonged moult by shedding their primaries at longer intervals and by extending the growth period of each primary. The longer primary moult and its earlier ending compared with coastal waders are probably adaptations to Wood Sandpipers' use of freshwater habitats, which in southern Africa provide unpredictable food supplies and might require nomadic movements between ephemeral inland wetlands.

Immature migrant waders have more complex patterns of primary moult than adults, but these have been described only fragmentarily. The Wood Sandpiper Tringa glareola breeds in the taiga region of the Palearctic and part of the population migrates to southern Africa. We selected this population for a study of the primary moult strategies of an immature wader. After analysing the moult formulae of 674 immatures, we discuss potential factors that influence the choice of moult strategy. All moulters replaced two to six outer primaries; 91% moulted four or five. We used the Underhill-Zucchini model to estimate the timing and duration of moult in immatures replacing different numbers of primaries. A slow moult of five or six primaries, adopted by 29%, lasted on average 98-111 days, beginning on average 8-16 December. Moult of four primaries (63%) began on 6 January and averaged 73 days. A rapid moult of three primaries (7%) began on 24 January and averaged 55 days. All groups ended their moult between 19 and 28 March. GLM models showed that heavier immatures were more likely to start moulting than leaner birds. This tendency was more pronounced in November-January than in later months. The later the moult started, the fewer feathers were replaced and the faster the process. Departure time set the limit for the end of moult. We suggest the ability to choose different strategies allows immature Wood Sandpipers to adjust their moult to the variable conditions they encounter at wetlands in southern Africa.