Effect of beaver activity on bird communities in Mediterranean riparian ecosystems

Riparian ecosystems in Mediterranean regions are biodiversity hotspots, despite facing increasing threats by human-induced pressures. The activities of keystone species, including ecosystem engineers, can enhance ecosystem resilience and biodiversity. The Eurasian Beaver acts as an ecosystem engineer, potentially increasing resilience and species diversity. In central Italy, where beavers have suddenly reappeared after centuries of absence, we evaluated their short-term effects on breeding bird communities. Using a paired design with 12 sites with beavers and 12 acoustically monitored control sites, we recorded 31 breeding bird species. In general, we found that mean bird species richness was higher at sites influenced by beaver activity. Beaver presence significantly altered community composition, increasing mostly the frequency of occurrence of two shrub-nesting species, Aegithalos caudatus and Sylvia subalpina, while non-limiting the occurrence of cavity- and canopy-nesting birds, thus suggesting that beavers may increase habitat heterogeneity. Beaver ongoing expansion in southern European rivers may provide a nature-based solution to counteract fragmentation and climate change impacts in threatened riparian ecosystems.