Changes in species abundance, distribution, and diversity in a central European bird community

We analyzed possible causes of changes in species abundance, range size, and diversity as well as extinctions and colonizations in a central Europenn bird community Using data from the semiquantitative ''Lake Constance'' breeding bird atlas, we demonstrated that changes in regional abundances from 1980/1981 to 1990-1992 of 151 coexisting bird species were influenced by breeding habitat and migratory status. Significant declines were found in populations of farmland species and long-distance migrants. Farmland species lost parts of their ranges but hardly changed in local abundance in sites where they still occurred. In contrast, declines in long-distance migrants were caused by significant declines in local abundance with only slight loss of occupied range. Regional extinctions and colonizations were predictable from overall population trends. For example, all species that went extinct were either farmland species or long-distance migrants. Avian community composition was influenced by disproportionate declines of abundant species. This led to declines in the total number of breeding pairs and in community biomass and to increases in community evenness, but Co only slight declines in species richness. Future conservation efforts in Europe need to focus more on farmland species and on understanding causes for the declines of long-distance migrants.