Numbers of mute swans and Whooper Swans in Sweden, 1967-2000
Forskningsoutput: Tidskriftsbidrag › Artikel i vetenskaplig tidskrift
Mute Swans (Cygnus olor) and Whooper Swans (Cygnus cygnus) in Sweden have been monitored as part of the International Waterbird Census (IWC) since 1967. For the Whooper Swan, midwinter indices show fluctuations around a slowly increasing trend. Country-wide surveys in 1971-72, 1988-89, 1995 and 2000, however found a more substantial increase in numbers, with national totals estimated at 2,000, 4,000, 8,000 and 8,000 individuals, respectively. The difference between the trends indices and the results of the country-wide surveys is attributable to the birds using more terrestrial habitats since the early 1980s, which are less well covered by the IWC. In 1995, 33% of the swans were found on land, compared to 43% in January 2000. For the Mute Swan, the midwinter indices showed a significantly increasing trend from 1970 to 2000, whereas autumn indices from September counts fluctuated around a more or less stable level, but with a decrease in the last few years. Country-wide midwinter counts recorded about 8,000 Mute Swans in 1973, 13,000 in 1988-89 and over 15,000 in january 1993.