THE DEVELOPMENT IN THE BREEDING BIRDS OF LAKE CONSTANCE - COMPARISON OF GRID MAPPING IN 1980/81 AND 1990/91

The distribution and number of breeding birds at Lake Constance was mapped on 278 grids of 4 km2 in 1990/91, covering 88.3% of the area of 1980/81. As only 25 % of the grids were censused by the same observers as in 1980/81, changes were only considered real if significant on the 2% level at least. This was the case in 62 species, 29 of which were increasing, 33 decreasing. A total of 145 breeding species was found (143 before), however, the number of species per grid and the total number of territories registered were lower than ten years ago. Apart from increases of species of urban settlements (eg. Feral Pigeon, Collared dove, Black Redstart, Serin) and forests (eg. Sparrowhawk, Goshawk, Great Spotted Woodpecker, Mistle thrush), the favourable development in species living in reedbeds and in waterbirds was notable. The latter is due to effective conservation measures at Lake Constance. Remarkable was the considerable loss in breeding numbers of the House Sparrow and the generally negative development of long-distance migrants, especially passerine species. A drastic population decline was found for almost the complete guild of ground-nesting birds in open habitats.