Andrzej Dylik, Tomek Królak, Leszek Wasielewski, Dariusz Węcławek
Ornis Polonica 2024, 65: 42–56
https://doi.org/10.12657/ornis.2024.1.3
Abstract: In the year 2017, a complete survey of the breeding population of the Rook Corvus frugilegus was carried out across the entire Kuyavian-Pomeranian Voivodeship. A total of 128 colonies of about 7,470 nests and 30 nests outside colonies (1–2 nests at 18 sites) were recorded, in total approx. 7,500 nests. There were 106 colonies in towns (82.8%) and 22 colonies in villages (17.2%). 5,449 nests were recorded in towns (73.0%) and 2,021 nests in villages (27.0%). On average, colonies in towns consisted of 51.4 nests (Me=17) and in villages of 91.9 (Me=31). There were no significant differences in colony sizes between towns and villages, nor were there differences in the distributions of colony prevalence in the distinguished size categories between towns and villages. The largest breeding colony of 923 nests was located in Lubień Kujawski. Colonies with up to 50 nests accounted for 71% of the total number, colonies with 51–100 nests for 13% and colonies with more than 100 nests for 16%. The average Rook density was 42 pairs/100 km2 of total area and 54 pairs/100 km2 of non-forested area. Between the years 2001–2002 and 2017, the population in the entire voivodeship decreased by about 31%, with an average decrease of 2.5% per year. For the five districts, the annual decline in abundance between 2002 and 2014 was smaller (3%) than between 2014 and 2022 (7.7%); the rate of decline in abundance in the second period was about 2.6 times higher. In the five districts with the longest data series, the mean annual rate of decline in abundance was 9% (λ=0.91). In 2017, nest abundance in urban areas was similar to 2001–2002, while in villages it decreased between the years 2001–2002 and 2017 by about 63%. The colony distribution in atlas grid cells in the voivodeship in 2017 was 19.1% (a decrease of about 60% compared to the years 1985–2004). Local and state administration authorities do not have up-to-date information on the number of breeding Rooks in their vicinity or this knowledge is at least incomplete and fragmentary, which may be relevant when issuing administrative decisions affecting the abundance of the Rook, which is on the list of species vulnerable to extinction in Poland. The downward trend in Rook abundance in the Kuyavian-Pomeranian Voivodeship is as strong and pronounced as in whole of Poland.
Keywords: Corvids, decrease of abundance, distribution, Rook Corvus frugilegus
