Ornis Hungarica. vol.12-13. (2003) p.191-199.
Monitoring Aquatic Warbler Acrocephalus paludicola in Poland
As a globally threatened species, the Aquatic Warbler requires a monitoring programme for population trends to be tracked. Such a programme should consider the timing of censuses to achieve 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 basin between 1995 and 1997 and in the Lublin area between 1993 and 1997. Densities of singing males 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 collected during 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 plots we recorded significantly higher numbers of singing males during the second count than in the first count. Increases in the numbers of singing males were recorded mainly in areas burnt or flooded in spring. In earlier surveys, such places often had been considered inappropriate for the Aquatic Warbler. We discuss some hypotheses concerning changes in the numbers of singing males between the first and second brood surveys. Extending the time of the second count until late June may be important in planning future conservation actions. Also, habitat features during second breeding attempts should be taken into account in the management of the breeding areas.