Łukasz Krajewski, Tomasz Chodkiewicz, Szymon Czernek, Agnieszka Grajewska, Krzysztof Henel, Michał Korniluk, Grzegorz Maciorowski, Piotr Marczakiewicz, Paweł Mirski, Grzegorz Neubauer, Rafał Szczęch, Piotr Świętochowski, Tomasz Tumiel
Ornis Polonica 2023, 64: 161-189
https://doi.org/10.12657/ornis.2023.3.1
Abstract: Dozens of publications have been devoted to the breeding avifauna of the Biebrza River Valley, one of the most important bird areas in Poland. However, there is a lack of up-to-date information on the population trends of many species. The paper summarises the results of surveys of selected bird species carried out in 2015–2022. During this period 178 species were confirmed or probable breeders. The area holds more than 80% of the national breeding populations of the Northern Pintail Anas acuta (0–20 females), Greater Spotted Eagle Clanga clanga (10–15 pairs), Short-eared Owl Asio flammeus (0–35 pairs) and Aquatic Warbler Acrocephalus paludicola (3,268–6,621 males) and over 50% of population of the Northern Shoveler Spatula clypeata (490), White-winged Tern Chlidonias leucopterus (0–2,950 pairs), Bluethroat Luscinia svecica (890 males) and Citrine Wagtail Motacilla citreola (60–120 pairs). Local populations of 22 species exceed 5% of the national population size. In the Biebrza River Valley, in the long term, declining trends (26 species) prevail over increasing ones (23 species). In case of most species, the changes in the size of the Biebrza populations reflect the situation of species in the whole Poland or Europe. This indicates the dominant influence of supra-regional phenomena on the avifauna of the Biebrza Valley. Among a few species whose trends do not correspond to changes on a larger spatial scale, the predominance of species whose Biebrza populations exhibit more positive trends than the national populations is evident. The rates of decline of some species is also slower. This suggests that the habitats of the species studied in the Biebrza Valley are in better condition than in other river valleys in Poland, stressing the key importance of this area for the conservation of wetland avifauna.
Keywords: long-term population trends, the Biebrza National Park, the Biebrza River, waterbirds, wetlands
