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Teasing out how species respond to human-induced environmental changes has become a priority for addressing the challenges posed by the need to conserve biodiversity. Although land abandonment is widespread, the threat it can represent to biodiversity remains poorly understood. To address this issue, we used data from eight long-term studies in a region with widespread land abandonment that has been identified as a biodiversity hotspot, the north-west Mediterranean Basin. We conducted a multi-site analysis of how changes in species occurrence were affected by species' attributes (habitat preference, habitat breadth, migration strategy and latitudinal distribution). The analysis revealed a nested pattern in the effect of species attributes. Woodland and shrubland species showed the strongest increase, whereas no change in overall occurrence patterns was detected in farmland species. Residents increased significantly, especially those with a northern distribution, whereas migrants decreased significantly, especially farmland species with a narrow habitat breadth. Changes in species occurrence were also related to initial landscape composition, with larger increases in initially woodland or mixed landscapes. Woodland species increased in all landscape types, shrubland species increased only in mixed landscapes, and farmland species decreased more, although not significantly, in farmland landscapes. Our results strongly support the hypothesis that large-scale habitat changes associated mainly with land abandonment are impacting bird community patterns in the Mediterranean region. Negative effects seem to be recorded mostly for migrants in farmland landscapes, suggesting that declines in these species are likely to be caused by a variety of mechanisms interacting with habitat change in the breeding region.
