This paper explores how environmental traits shape the winter distribution of passerine (O. Passeriformes) richness in the south-western Palearctic, a major wintering ground for the European avifauna. We apply three complementary approaches. First, we assess the way climate, landscape and habitat affect species richness by means of field counts across the study area. Second, we model the spatial distribution of six common passerines using ring recoveries as presence data. Finally, where the resulting models predict the actual distribution of birds, we employ the models to forecast the future distribution of richness according to predictions of climate change, i.e. of increasing temperature and decreasing precipitation. The results support an effect of landscape, habitat structure, temperature and precipitation on bird richness. Distribution models fit the actual distribution of bird richness and their predictions suggest that winter species richness will decrease in lowlands and increase in highlands. This pattern could be related to direct effects of temperature on thermoregulatory costs and indirect effects on winter primary productivity affecting food resources. These results also indicate that, in a context of climate warming, species-rich sectors will shift from lowlands to highlands, suggesting that uplands will have a regulatory role in the future winter distribution of birds.
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