Ecosystem Engineers at Work: How Beaver Ponds Reshape Avian Abundance and Diversity in a Mountainous Forest Ecosystem...

By building dams and creating ponds, the Eurasian beaver (Castor fiber) acts as an ecosystem engineer, generating habitats for species that depend on wetland and freshwater ecosystems, which are increasingly threatened worldwide. Birds in particular may benefit from these habitats as feeding or breeding grounds. To assess the effects of beaver ponds on avifauna communities, we conducted six 20-min bird counts between April and June 2021 at 15 beaver ponds and 15 control plots along unmodified streams in the Bavarian Forest National Park, where natural freshwater habitats are scarce. In total, 46 bird species were recorded, of which 13 occurred exclusively at beaver ponds and three only at control sites. Using multiple regression analysis, we investigated the effects of beaver ponds, pond size and a set of environmental variables including habitat openness, standing dead wood and the proportion of deciduous and coniferous trees. Bird abundance was 23% higher at beaver ponds than at control sites. In particular, species associated with aquatic habitats for feeding and breeding occurred at significantly greater abundances at beaver ponds. Species richness and abundance increased with pond surface area, and the largest ponds supported the most distinct bird communities as well as the highest richness and abundance. Moreover, bird community composition differed significantly between beaver ponds and control plots. Our findings demonstrate that beaver-created wetlands substantially alter bird community composition and enhance habitat availability for wetland-associated species. These results highlight the important role of beavers as ecosystem engineers in increasing avian diversity and promoting habitat heterogeneity in forest ecosystems.