Arkadiusz Sikora, Maria Wieloch, Przemysław Chylarecki
Ornis Polonica 2012, 53: 69–85
https://doi.org/10.12657/ornis.2012.2.0
Abstract: Whooper Swan breeds in almost all regions of Poland except the mountains and foothills. In years 1973–2011 the annual average growth rate of breeding population was 12%. In 2007 the national breeding population was estimated at the level of 43–52 pairs, while in 2011 at 73–80 pairs. It is likely, that even 80–90 pairs breed in Poland. In 2007–2011 the average rate of annual population increase was 18% for a subpopulation breeding on the northern lake districts, and 35% for swans nesting in the southern highlands. The number of pairs breeding on lowlands of central Poland fluctuated, despite an increasing trend had been shown there previously. Occupancy (the frequency of occupied 10 × 10 km squares) increased from 1.3% in 2007 to 2.0% in 2011, while the cumulative occupancy for the 5-year period was 2.7%. Occupancy increased at the highest rate in the lake districts of northern Poland. Fish ponds were key breeding habitats – c. 60% of all occupied sites across the country. 16% of sites were located on lakes, 8% on dam and storage reservoirs and 7% on floodplains in river valleys and in the polders. Fish ponds were main breeding habitats used in the southern and central Poland (100% and 75% breeding sites, respectively). Fish ponds (41% sites) and lakes (31%) dominated among occupied breeding sites at the lake districts of northern Poland. Overall, 58% of pairs breeding successfully raised broods. An average brood size early in the season (1 May–10 June) was 4.03 cygnets (range: 1–10, N=108), while late in the season (21 July–31 August) it dropped to 3.51 (range: 1–8, N=154). Four types of partnerships were found (N=297): Whooper Swan pairs (95% of cases), 3 Whooper Swans (3 cases), a mixed pair of Whooper Swan and Mute Swan Cygnus olor raising chicks (1 case) and a trio composed of a pair of Mute Swans and single Whooper Swan (11 cases at 4 sites).
