Between Summer and Spring: Temperatures Along Migration Routes and at Wintering Grounds Shape Spring Migration Timing in Dunnocks (Prunella modularis)

Climate change shifts bird migration timing, but its influence on medium-distance migrants is understudied. We investigated how temperatures across Europe influence the dunnock’s spring passage timing, using daily standardised ringing data from spring migration (26 March–16 May) at Hel Peninsula (N Poland, Baltic coast) over 1965–2025. We determined multi-year trends in the dates of the beginning (10% of passage = p10), median (p50), end (p90), and migration duration (MD = p90–p10) of dunnocks. We also tested the effects of temperatures, averaged for months of breeding (two parts: May–June, July–August), wintering (November–February), autumn (September–October) and spring (March–May) migrations, in four regions of Europe, on the dates of these percentiles during 1965–2025, using multiple linear regression. All phases of passage advanced by 5–8 days; MD remained stable over the 61 years. All phases were early with warm springs in central and southern Europe; p10 and p50 were delayed after warm winters. The p10 was early after warm summers in northern Europe. This shows that climate warming in Europe benefits dunnocks, but their decline across Europe suggests that habitat changes and extreme weather counteract these benefits. Understanding these trade-offs for medium-distance migrants is crucial for their conservation.