Many migrant European birds have been departing their breeding grounds earlier in recent decades in response to rising temperatures from climate change. We examined long-term changes in the autumn migration timing of immature Garden Warblers using data from ringing station Bukowo-Kopań on the Polish Baltic coast in 1967–2018. We calculated an Annual Anomaly (AA) of migration and the dates when 10%, 50% and 90% of migrating birds were caught at each station. We modelled AA and the dates of these percentiles of passage for each station against the year and bi-monthly spring, summer and autumn temperatures as explanatory variables in multiple linear regression models. The overall passage (AA) of immature Garden Warblers advanced by 7 days and the dates of the 50th and 90th passage percentiles advanced by 6–11 days. Overall passage, and dates for 50% of passage occurred later the higher summer temperatures rose in Finland. We suggest favourable foraging conditions in warm summers at these breeding grounds and at first stopover sites delayed the passage because these inexperienced birds took advantage of the conditions to accumulate fuel before migrating south. The overall passage, and the dates of 10%, 50% and 90% of autumn passage occurred the earlier the higher were spring temperatures on spring migration route in Italy, and the higher were mean summer temperatures at breeding grounds in southern Sweden and Norway. We suggest a trans-generation carry-over effect, as warm springs encourage early arrival and nesting of returning adults, thus earlier broods and hatching of juveniles, which also grow faster in warm summers. These effects enable immatures to migrate earlier in autumn after a warm breeding season. The long-term increase in Europe’s spring and summer temperatures thus help explain the shift in Garden Warblers’ migration timing.

Sex-specific adjustments of bird migration phenology to climate change are understudied. We analysed blackcap migration timing using spring (26 March–16 May) ringing data from Bukowo-Kopań (N Poland) in 1982–2025. We assessed the influence of large-scale climate indices in winter (December–February) and spring (March–May) on the beginning (p10), median (p50), and end (p90) of passage of each sex, using multiple regression. Protandry (earlier arrival of males) at the beginning of passage averaged 2.2 days and remained stable over 44 years, because p10 dates advanced by 9 days in both sexes. This aligns with 22-year studies from northern Europe, and with the mating opportunity hypothesis. The median (p50) of passage advanced by 7–9 days, but p90 showed no trends during 1982–2025. Positive winter and spring North Atlantic Oscillation (NAO) and spring Scandinavian Pattern (SCI) were associated with early p10 and p50, and positive winter Indian Ocean Dipole (IOD) with delayed p90, in both sexes alike. These similar responses likely occur because these climate patterns affect broad non-breeding areas of both sexes. We suggest that female blackcaps are as adaptive as males, and advanced migration maximises reproductive success and the chance for second broods of both sexes.

Sex-specific adjustments of bird migration phenology to climate change are understudied. We analysed blackcap migration timing using spring (26 March–16 May) ringing data from Bukowo–Kopań (N Poland) in 1982–2025. We assessed the influence of large-scale climate indices in winter (December–February) and spring (March–May) at the beginning (p10), median (p50), and end (p90) of passage of each sex, using multiple regression. Protandry (earlier arrival of males) at the beginning of passage averaged 2.2 days and remained stable over 44 years, because p10 dates advanced by 9 days in both sexes. This aligns with 22-year studies from northern Europe, and with the mating opportunity hypothesis. The median (p50) of passage advanced by 7–9 days, but p90 showed no trends during 1982–2025. Positive winter and spring North Atlantic Oscillation (NAO) and spring Scandinavian Pattern (SCI) were associated with early p10 and p50, and positive winter Indian Ocean Dipole (IOD) with delayed p90, in both sexes alike. These similar responses likely occur because these climate patterns affect broad non-breeding areas of both sexes. We suggest that female blackcaps are as adaptive as males, and advanced migration maximises reproductive success and the chance of second broods in both sexes.