Fluctuations and trends in the numbers of staging waterbirds in south Sweden in September 1973—2013

Abstract

Regular September counts of staging waterbirds have been undertaken annually in south Sweden since 1973 as a complement to the International Midwinter Counts undertaken in January each year since 1967. The September counts aim to cover the population development of staging waterbirds, especially relating to species that are not wintering in the country. Between 150 and about 200 sites have been included in the calculation of the September indices, using the TRIM method. September indices were calculated for 18 species. The trends over the entire 41-year period were significantly increasing for all but five species (Anas platyrhynchos, Somateria mollissima and Mergus serrator decreasing, whereas Podiceps cristatus and Fulica atra did not show any clear long-term trend). The September indices were in good agreement with the International Midwinter Counts and the winter counts of the Swedish Bird Survey, but much less well with migration counts at Falsterbo and breeding season counts of the Swedish Bird Survey. For the last ten years of the series, six species showed a significantly increasing trend, whereas four species decreased.