Tomasz Tumiel, Paweł Białomyzy, Michał Budka, Marcin Dojlida, Krzysztof Henel, Łukasz Krajewski, Piotr Marczakiewicz, Eugeniusz Pugacewicz, Marta Potocka, Piotr Świętochowski
Ornis Polonica 2024, 65: 171–183
https://doi.org/10.12657/ornis.2024.3.1
Abstract: This study presents changes in the population size of the Black Grouse Lyrurus tetrix in the North Podlasie Lowland in the years 2006–2023. The population was assessed on the basis of the number of males present at lekking sites. During the study period, the distribution of Black Grouse in the macro-region was limited to three isolated areas: Biebrza, Białystok–Narew, and Bielsk–Drohiczyn. In the years 2006–2009, the population of Black Grouse was estimated at 196–209 males across 58 lekking sites. By 2013–2016, this number had decreased to 64–70 males across 28 sites, and by 2020–2021, only 20–24 males remained at 12 sites. In the subsequent years, a further decline was observed, with only 4–5 males recorded in 2023, located solely in the Biebrza Basin and at one lekking site in the southern part of the region. Between 2006–2009 and 2023, the Black Grouse population in the North Podlasie Lowland decreased by 98%. Throughout the study period, the largest population was found in the Biebrza Basin. The most significant declines in the Knyszyn Forest and the Biebrza Basin were recorded between 2009–2010 (–27%), 2010–2011 (–37%), and 2013–2014 (–54% in the Biebrza Basin alone). The average number of males per lekking site decreased over time, with 3.8 males in 2006–2009 (N=58), 2.3 males in 2013–2016 (N=28), and 1.9 males in 2020–2021 (N=12). During the study, 8 collective lekking sites, 53 partially dispersed sites, and 175 dispersed or single-male sites were identified. Collective lekking sites were only found in the Biebrza area throughout the study. From 2009–2023, the number of juveniles per successful female was 1.3 (N=17). The catastrophic decline in the Black Grouse population is likely due to a wide range of factors, most notably habitat changes caused by the overgrowth of biotopes, drying out, and transformations due to agricultural and forestry practices, as well as predation, particularly by the Red Fox Vulpes vulpes. Other significant threats, in our opinion, include climate change and unstable weather conditions, which reduce the chance of chick survival, and increasing spatial isolation of the remaining local populations.
Keywords: Black Grouse, decline of population, lekking site, Lyrurus tetrix, North Podlasie Lowland
