Implementation of irrigation in a Mediterranean agro-forestry mosaic reduces species richness and creates structural changes in a wintering passerine community

Agricultural intensification, particularly shifts from traditional rainfed to irrigated crops, profoundly alters habitats and biodiversity. In this work, we examined the effect of such transformations on a wintering passerine assemblage in a Mediterranean agro-forestry mosaic in Spain. Sampling was conducted in a reed bed area used as a roosting site for several passerine species that depend on surrounding cropland to feed, during winters 2004/05-2006/07 (pre-irrigation) and 2021/22-2023/24 (post-irrigation). Findings reveal a significant reduction in species richness (from 24 to 12 species) as confirmed by rarefaction analyses. Assemblage composition shifted markedly, with specialist seed-eaters declining, whilst wetland-adapted species increased. Such result aligns with the expected ecological impact of irrigation, which simplifies habitats and favors generalist species, underscoring the biodiversity impact of irrigation policies. Such transformation contributes to deteriorating Spain’s role as a critical wintering ground for several European species. Our findings appeal to an urgent need for adaptive management policies to mitigate biodiversity loss in Mediterranean agro-ecosystems under agricultural intensification. Future research should explore broader regional impacts and the interplay of climate change with irrigation-driven biodiversity shifts.