Breeding Bird Dynamics in a Primeval Temperate Forest Over Thirty-Five Years: Variation and Stability in the Changing World

Abstract

The composition and structure of the breeding bird assemblage in the Bialowieza National Park (BNP) were documented in 2005-2009 and compared with the data from the previous 30 years. Mapping censuses were carried out in seven plots located in three forest types: ash-alder riverine, oak-hornbeam, and mixed coniferous forest. We checked whether the bird community composition had remained stable over the 35 years and the extent to which the numeri- cal trends in BNP followed the regional trends. The composition of breeding avifauna and species richness was basical- ly unchanged, except for the strongly increasing Sylvia atricapilla, which became a regular dominant in all habitats. The density gradient across habitats — highest in the riverine, lowest in the coniferous stands - was retained. After a max- imum in 2001, the numbers of birds declined slightly, but densities were still among the highest in 35 years. Numbers of 18 of the 26 commonest species were higher in 2005-2009 than in 1975-2009; only Anthus trivialis, Phylloscopus sibila- trix, Ficedula parva showed negative trends, and Ficedula hypoleuca almost went extinct recently. Some numerical changes were attributable to local habitat changes (increases in Phylloscopus collybita and Sylvia atricapilla, declines in spruce- dependent species). Numbers of only four of 22 species (Dendrocopos major, Erithacus rubecula, S. atricapilla, Parus major) changed concurrently in BNP and the rest of Poland. The apparent lack of a relationship between changes in bird num- bers and the local and regional situation suggests that factors acting on a far larger scale could have been involved. Despite these numerical changes, the breeding bird assemblage of primeval temperate forest stands out as an example of remarkable stability.