Tomasz Buczek
Ornis Polonica 2024, 65: 295–323
https://doi.org/10.12657/ornis.2024.4.2
Abstract: This paper presents the species composition, dominance structure and density of the passerine bird community breeding on Chełm Calcareous Marshes (Chełmskie Torfowiska Węglanowe, eastern Poland) in a Special Protection Area Natura 2000 PLB060002. Observations were carried out on three census plots located in the rushes of Cladietum marisci. This plant community is typical for alkaline fens and covers a significant area (753 ha). The census plots were marked on three fens: Roskosz (R), Tarnowo (T) and Bagno Serebryskie (B). The counting was carried out in each area in the years 2008–2011 and in 2022. On each plot, the censuses were repeated twice, in 2008–2011 and in 2022. The comparative analyses used the results of research conducted by other authors on the R and T plots in the years 1992–1993. The counts were carried out using a combined territory mapping method (Enemar’s method). Between 6 and 12 counts were carried out on the plots per season. Observations spanning three decades showed stability in species composition (mean Sørensen similarity index QS = 77.8) and dominance structure (mean Renkonen similarity index Re = 68.8). Avian community on the studied plots was dominated by species characterized by different local trends in abundance: the Aquatic Warbler Acrocephalus paludicola – decline or disappearance (in the years 1992–2008, it was the dominant species on all plots), Reed Bunting Emberiza schoeniclus – a stable population, Sedge Warbler A. schoenobaenus and Savi’s Warbler Locustella luscinioides – a distinct increase. The observed trends depended only slightly on stable local habitat conditions including water depth, height of reed vegetation or the degree of bush cover. Dominants were accompanied by the Common Grasshopper Warbler L. naevia, Meadow Pipit Anthus pratensis and Whinchat Saxicola rubetra. The mean density of the community was 15.9 pairs/10 ha. The comparison of the studied plots with passerine bird communities inhabiting lowland marshes in Poland where the Aquatic Warbler was ranked as the first or second in dominance, revealed high similarity in species composition (mean Sorensen’s similarity index QS = 73.8; N = 14) and similarity in dominance structure (mean Renkonen similarity index Re = 64.1; N = 14). The conditions prevailing in the country fens favor the Aquatic Warbler as an extreme habitat specialist, and also provide favorable conditions for species with a wide habitat tolerance, such as Reed Bunting and Sedge Warbler. In habitats dominated by the Aquatic Warbler, other species find suboptimal living conditions, which is reflected in their low densities.
Keywords: Aquatic Warbler, bird community, Chełm Calcareous Marshes, Common Grasshopper Warbler, density, dominance, Reed Bunting, Savi’s Warbler, Sedge Warbler
