Monitoring Aquatic Warbler Acrocephaluspaludicola in Poland

As a globally threatened species, the Aquatic Warbler requires a monitoring programme forpopulation trends to be tracked. Such a programme should consider the timing of censuses toachieve precise assessments of the number of the singing males within the limited singing period.We compare results of whole-population counts conducted in the southern Biebrza basinbetween 1995 and 1997 and in the Lublin area between 1993 and 1997. Densities of singingmales showed different trends for selected fen mire patches within the same wetland complexes.Based on the results of the nationwide census in Poland (1997), we compare data collectedduring two breeding season counts (between 20 May-6 June and 17 June-3 July respectively)relevant to the timing of the first and second breeding attempts. On most census plotswe recorded significantly higher numbers of singing males during the second count than in thefirst count. Increases in the numbers of singing males were recorded mainly in areas burnt orflooded in spring. In earlier surveys, such places often had been considered