A comparison between ringing totals at Falsterbo, SW Sweden, ringing totals at Ottenby, SE Sweden, and point counts from the Swedish Breeding Bird Census during 20 years (1980—1999)

Abstract

Autumn ringing totals from Falsterbo, SW Sweden, and Ottenby, SE Sweden, and data from the Breeding Bird Census were compared in 37 species during 1980—1999. We compared both 20-year trends (continuity of changes) and mean totals for the 1980s and 1990s, respectively. The three programmes showed similar patterns in many species. More species showed decreasing than increasing trends. There were no significant differences in the number of significant trends between the three programmes or between the numbers of significantly decreasing trends among long-distance and other categories of migrants. The two-decade comparison showed more negative changes among long-distance than among other migrants at Falsterbo, and long-distance migrants decreased most at Falsterbo and least in Point Counts. Possible reasons for the differences are (a) different populations, especially between Falsterbo and Ottenby, (b) trends in partial migrants may not be detected in ringing totals, (c) non-random route selection in Point Counts, (d) difficult to count very common species in Point Counts, and (e) decreases of more species in Western than in Eastern Europe, affecting Falsterbo.