Acoustic monitoring shows invasive beavers Castor canadensis increase patch-level avian diversity in tierra del fuego.
Abstract
The North American beaver Castor canadensis is an invasive species in the Tierra del Fuego Archipelago. Due to this biological invasion, Argentina and Chile signed an agreement to restore affected ecosystems by eradicating beavers. In southern Patagonia, the beavers' ecological impacts are well studied, but there is a relative lack of information on how their invasion (and potential removal) could affect bird communities. In the southern portion of Tierra del Fuego's 'big island' (Isla Grande), we conducted passive acoustic monitoring and avian point counts in intact riparian forests, beaver ponds and beaver meadows (i.e. drained ponds) to assess spatial and seasonal differences in acoustic activity and avian abundance, species diversity and functional diversity. During spring and summer, acoustic activity was significantly higher in meadows than in forests, with ponds exhibiting intermediate values. Abundance and species diversity exhibited similar patterns, driven largely by resident passerines, while functional diversity tended to be highest in ponds, largely due to ducks and raptors. Effects were weaker in fall and winter. Acoustic metrics exhibited moderate to strong correlations with all point-count-derived metrics. Synthesis and applications. At the patch level, the avian community was more abundant and diverse in beaver-modified habitats than in intact riparian forests, though communities in modified patches may not differ substantially from those in analogous natural open and wetland habitats. Dam breaching and pond drainage did not yield a return to an intact forest bird community, indicating that active reforestation may be necessary to restore avian communities to pre-beaver conditions in the short to medium term, as sought by the binational agreement. Given the immense challenges of eradication and restoration, its social-ecological costs and benefits-including those related to avifauna-should be thoroughly considered in establishing goals or indicators of success.