The importance of bioacoustic sampling for bats in Neotropical wetlands: new records for the Upper Paraná River floodplain.

Abstract

Bats provide essential ecosystem services and are highly dependent on freshwater resources. Wetlands are vital habitats for insectivorous and piscivorous species, but bats are often under-sampled in inventories that use traditional methods. The floodplain of the upper Paraná River is a biodiverse region threatened by the expansion of urbanisation, agriculture and livestock farming, and water regulation. Previous studies on bats, based exclusively on mist nets over a decade ago, recorded 17 species, predominantly frugivorous. In this study, the list of bat species was updated and feeding habits were assessed, employing bioacoustic methodology for the first time in the region. Acoustic monitoring was carried out in the Paraná, Baía and Ivinhema sub-basins during the dry and wet seasons of 2025. Using bioacoustics, 20 species/sonotypes were recorded, of which 18 species are new records for the plains, including one new record for the state of Paraná (Promops centralis). Combined with historical mist-net data, the current regional list comprises 35 species. Studies using mist nets alone captured mainly frugivores, whilst bioacoustics revealed a predominance of insectivores, shifting the overall composition of feeding habits to 60% insectivores, 28.6% frugivores, with the remainder comprising piscivorous, omnivorous, carnivorous and hematophagous species. Notably, bioacoustics detected three species of ground-dwelling bats (Noctilio albiventris, Noctilio leporinus and Myotis ruber), highlighting the importance of aquatic habitats for these species. The results demonstrate that bioacoustics is a very important tool for bridging the Wallacean gap in bat communities in wetlands, proving effective for sampling groups of species that are typically undersampled by conventional methods. We conclude that comprehensive bat conservation strategies in tropical floodplains and other aquatic ecosystems require the integrated use of mist nets and acoustic monitoring to accurately document biodiversity and plan effective conservation policies. Within the biodiversity of the Upper Paraná River floodplain, bats perform important ecosystem services such as controlling populations of emergent aquatic insects, energy transfer between aquatic and terrestrial environments, and seed dispersal for the maintenance of riparian forests.