Habitats of the globally threatened Aquatic Warbler(Acrocephalus paludicola) in Pomerania — siteconditions, flora, and vegetation characteristics

摘要

The Aquatic Warbler is the only globally threatened passerine bird species in Europe. Around 1900, itwas one of the most abundant birds in European fen mires. The population severely decreased as aconsequence of extensive wetland drainage. In recent years, it has been rather stable in key breedingsites but has decreased sharply in its westernmost occurrence Pomerania. Conservation of the Po-meranian birds is of key importance for conserving the intraspecific diversity of the species. Throughout 2004-2006 we studied all current breeding sites of the species in Pomerania. Twoareas have been studied in more detail: Rozwarowo Marshes, the largest breeding site in Pomerania,and Lower Oder Valley National Park, the last breeding site in Germany. Data on vegetation composi-tion and height, water level, site conditions, and land use were analysed. -The sites near the coast and in small river valleys are characterised by sparse and low Phragmitesaustralis stands with a well-developed lower sedge and herb layer. The sites in the Lower Oder Valleyare more nutrient-rich and dominated by Carex acuta, Phalaris arundinacea, and other meadowgrasses. In Rozwarowo Marshes, the birds inhabit sparse, short Phragmites australis and Thelypterispalustris vegetation that is maintained by winter reed cutting. In the Lower Oder Valley National Park,Aquatic Warblers shifted from Caricetum gracilis to other plant communities that continued to bemown frequently. Similar to the Lithuanian Aquatic Warbler habitats in the Nemunas Delta and incontrast to the predominantly mesotrophic habitats of the core population, the Pomeranian habitats areeutrophic and more influenced by inundation. Various rare and threatened plant communities occurhere. The Aquatic Warbler can be regarded as an umbrella species for mesotrophic and slightly eutro-phic peatlands for which this bird is a specialist. Conservation activities should focus on a site-specif-ic management and the prevention of further eutrophication.