Status of the Mute Swan, Cygnus olor and the Whooper Swan C. cygnus in Silesia (SW Poland)

Abstract

The Mute Swan became extinct as the breeding species in Silesia in 1880. It started to breed again in this region in 1948. Single pairs nested in a few places up to the second half of the 1960s. Since this time the Silesian population of the Mute Swan has been increasing. About 400 breeding pairs were found there in 1988-89 and approximately 110 of them nested on fish pond complexes in the Barycz Valley. The number of non-breeding swans was estimated at 1,800 birds in 1988 and 2,500 in 1989. The winter population of the Mute Swan has been increasing slowly. In the last years up to 3,000 swans wintered in Silesia. The most important winter ground was the Odra river where up to 70% of all wintering swans occurred. They preferred the upper course o f this river. Since the second half of the 1970s the Mute Swan has wintered in towns. Up to 60% of swans were found on 50 km of urban river sections in 11 cities. This value was smaller during mild and warm winters. The percentage of first winter Mute Swan varied between 17% and 36%. The first breeding pair of the Whooper Swans was found in Silesia (Odra Valley near Glogow) in 1983 and since this time up to four pairs have nested there every year. In addition, one pair was recorded in the western part o f the Barycz Valley in 1984. Further growth of the Silesian population of the Whooper Swan is possible because adult non-breeding birds were observed in both areas during the spring period every year. The winter population of this species was small (up to 146 birds) and the percentage of one year old swans varied between 3.8% and 23%.