Arkadiusz Sikora, Waldemar Półtorak
Ornis Polonica 2019, 60: 285–299
https://doi.org/10.12657/ornis.2019.4.3
Abstract: A total of 43 pairs of Common Cranes Grus grus (density of 0.6 pairs/10 ha) were counted in the nature reserve Bielawa (721 ha), comprising the largest Polish peatbog. Six other pairs nested near the reserve border. This indicates an increase by 10 times compared to the early 1980s. In the eastern part of the reserve (72 ha) a colony of 26 pairs (3.6 pairs/10 ha) were found. In 1983–2018 the number of Cranes counted during autumn surveys increased by 5 times (max. 2220 ind. in 2018), and by 2–3 times in spring (max. 1320 ind. in 2014 and 1070 ind. in 2018). In January 2018 a total of 250 and in 2020 – 390 wintering individuals were recorded. In the early 1980s 10 pairs of Wood Sandpipers Tringa glareola nested in the reserve, while in 2018–2019 only 1–2 males exhibiting courtship displays were observed, which suggests a strong population decline. During the last 15 years breeding of single pairs was recorded in four seasons. Throughout the last decade a few other breeding species were recorded, including the Whooper Swan Cygnus cygnus (1 pair), Greylag Goose Anser anser (up to 10 pairs), Gadwall Anas strepera (1 pair) and Citrine Wagtail Motacilla citreola (10 pairs in 2014). Conservation measures undertaken in the reserve Bielawa, including the reduction of water outflow and evaporation, as well as logging of expansive birches, helped to improve conditions for the local avifauna.
Keywords: Atlantic peatbog, colonial nesting, Common Crane, Grus grus, hydrological conditions, northern Poland, population decline, population growth, Tringa glareola, Wood Sandpiper
