Flyway-scale migration phenology identifies mismatches between migration timing and European hunting regulations.

The study of bird migration timing is pivotal for the identification of the onset of pre-breeding migration, when, according to the European regulatory framework, the hunting seasons should end following Article 7.4 of the EU Birds Directive. Member States may use different data sources, including citizen science platforms, to determine this onset. Here, we used data from eBird, a citizen science platform, to describe the timing of pre- and post-breeding migration of the Song Thrush (Turdus philomelos) across the Western Palearctic. For EU Member States, we compared the onset dates of pre-breeding migration we derived from eBird with those obtained from ringing data published in the Eurasian-African Bird Migration Atlas and with those reported in the EU Key Concepts Documents (KCD). We found high agreement between eBird and Atlas estimates, but substantial differences between KCD-defined onset dates and those identified in the Atlas and this study. This suggests that, in many EU Member States, hunting remains open after the onset of pre-breeding migration, with potential negative effects on breeding populations. This mismatch highlights the limitations of current country-specific definitions and the need for harmonized flyway-scale assessments of migration timing. As required by current EU legislation, hunting closure periods should rely on up-to-date scientific evidence and transparent national data-collection mechanisms. The systematic application of the method presented here to citizen science or ringing data provides a reproducible and standardized approach that can be adopted at the EU level, easily upgradeable as new data become available.