Szymon Beuch, Przemysław Wylegała
Ornis Polonica 2026, 67: 22-42
https://doi.org/10.12657/ornis.2026.1.2
Abstract: A survey of all known breeding sites of the Grey Heron Ardea cinerea in Poland was conducted in 2020–2025. Breeding was confirmed at 236 sites in total (178–199 per season). The species was most widespread (based on a 10 × 10 km grid) in northern and western Poland, particularly in Warmia and Masuria (15.8%), Greater Poland (9.5%), Pomerania (8.1%), and the Lublin region (8.4%), while the lowest occurrence was recorded in central Poland (Kuyavia– 1.6%, Łódź region – 2.1%). Most colonies (73–74%) were located in the coastal zone and lake districts, and the fewest (6–7%) in mountainous areas, with the highest site situated in the Sudetes at 580 m a.s.l. The national population was estimated at 11,139–13,190 breeding pairs. The largest numbers were recorded in Pomerania (2,371–2,686 pairs), Warmia and Masuria (2,001–2,428), and Greater Poland (1,803–2,067). Mean density in Poland was 38.3 pairs/1,000 km² (SD = 2.9). The national population trend in 2020–2025 showed a statistically significant moderate increase (λ = 1.0335, SE = 0.0073). Colonies with 1–50 nests predominated (61.3%), whereas large colonies exceeding 200 nests were rare (3.9%); the largest colony was at Helenów in Greater Poland (318–393 nests). The mean number of occupied nests per colony was 64.3 pairs (SD = 61.6), decreasing along a north-south gradient. The largest colonies occurred along the coast and in lake districts (73.5 and 70.2 pairs), and smaller ones in uplands, lowlands, and mountains (63.0, 59.3, and 42.8 pairs, respectively). Tree colonies constituted 89.0% (N = 210) of all sites, while colonies in willow Salix sp. thickets and in water margin communities constituted 5.1% (N = 12), and 5.9% (N = 14), respectively. Most nests were built on pines (46.1%) and alders (16.6%). Mixed colonies were recorded with the Great Cormorant Phalacrocorax carbo (11.4% of sites), Great Egret A. alba (7.6%), Black-crowned Night Heron Nycticorax nycticorax (3.0%), Rook Corvus frugilegus (0.8%), and Little Egret Egretta garzetta (0.4%). Over the past 50 years, the Grey Heron population in Poland has shown a slight increase, accompanied by range expansion into southern regions, including mountainous areas. The most dynamic increases occurred in southern Poland, whereas in other regions the population remained generally stable, with short-term increases recorded locally. 34–35% of the national population bred within Natura 2000 Special Protection Areas.
Keywords: breeding colonies, distribution, heronries, Natura 2000 sites, population size, population trends
