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RESEARCH PRODUCT

Potential Impact of Global Climate Change on Species Richness of Long-Distance Migrants

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Little evidence exists demonstrating that global climate change leads to systematic changes in the struc- ture of ecological communities. For avian communities, one would expect warmer winters to lead to declines in numbers of long-distance migrants if resident birds benefit from warmer winters and impose increasing competi- tive pressure on migrants. To study the potential influence of global climate change on long-distance migrants, we correlated the number of all species of land birds and the number and proportion of long-distance migrants, short- distance migrants, and residents in 595 grid cells across Europe. We used mean temperature of the coldest month, mean spring temperature, and spring precipitation as measures of climatic conditions in winter and during the breeding period. The number and proportion of long-distance migrants decreased with increasing winter tempera- ture, decreasing spring temperature, and increasing spring precipitation. We used this spatial relationship between bird community structure and climate in Europe to make predictions about changes in bird communities of the Lake Constance region, Central Europe, between two census periods (1980-1981 and 1990-1992). Winter temper- ature in this region increased significantly between the two censuses, whereas spring temperature and precipita- tion did not change. As predicted from the models, the proportion of long-distance migrants decreased and the number and proportion of short-distance migrants and residents increased between the two censuses. The signifi- cant declines of the long-distance migrants in the Lake Constance region are of a magnitude that can be explained by the observed climate change. Our results suggest that increasingly warmer winters may pose a more severe threat to long-distance migrants than to the other bird groups.