The alarmingly threatened Aquatic warbler: from early ecological insights to current conservation priorities

The Aquatic warbler ( Acrocephalus paludicola ) is the rarest songbird of continental Europe and a fen mire specialist. The systematic drainage in the eighteenth and nineteenth centuries resulted in the loss of almost all fen mires in the breeding range. In our conservative and cautious estimate, we assume that the total historical population was around 1 million singing males. The current population is estimated to have fallen in 2025 to approximately 4200 singing males, that is, less than 0.5% of the past population size. The heavily fragmented breeding sites now comprise a total of just 382 km ² . Due to increased isolation of breeding sites, today it may be more difficult for Aquatic warblers to cope with temporary catastrophe‐related losses of habitat by performing short‐ and long‐distance movements within the breeding period. Although the causes of decline are understood and effective conservation measures are known, the Aquatic warbler is on the brink of extinction.