Optimizing bat bioacoustic surveys in human‐modified Neotropical landscapes

Abstract

During the last decades, the use of bioacoustics as a non-invasive and costeffective sampling method has greatly increased worldwide. For bats, acoustic surveys have long been known to complement traditional mist-netting, however, appropriate protocol guidelines are still lacking for tropical regions. Establishing the minimum sampling effort needed to detect ecological changes in bat assemblages (e.g., activity, composition, and richness) is crucial in view of workload and project cost constraints, and because detecting such changes must be reliable enough to support effective conservation management. Using one of the most comprehensive tropical bat acoustic data sets, collected in the Amazon, we assessed the minimum survey effort required to accurately assess the completeness of assemblage inventories and habitat selection in fragmented forest landscapes for aerial insectivorous bats. We evaluated a combination of 20 different temporal sampling schemes, which differed regarding number of hours per night, number of nights per site, and sampling only during the wet or dry season, or both. This was assessed under two different landscape scenarios: in primary forest fragments embedded in a matrix of secondary forest and in the same forest fragments, but after they had been re-isolated through clearing of the secondary forest. We found that the sampling effort required to achieve 90% inventory completeness varied considerably depending on the research aim and the landscape scenario evaluated, averaging~80 and 10 nights before and after fragment re-isolation, respectively. Recording for more than 4 h per night did not result in a substantial reduction in the required number of sampling nights. Regarding the effects of habitat selection, except for assemblage composition, bat responses in terms of richness, diversity, and activity were similar across all sampling schemes after fragment re-isolation. However, before re-isolation, a minimum of four to six sampling hours per night after dusk and three to five nights of sampling per site were needed to detect significant effects that could otherwise go unnoticed. Based on our results, we propose guidelines that will aid to optimize sampling protocols for bat acoustic surveys in the Neotropics.

Passive acoustic monitoring reveals the role of habitat affinity in sensitivity of sub‐tropical East Asian bats to fragmentation

“…In islands, where more than one detector was deployed, we primarily chose their locations by maximizing the distance between them and thus enlarging the spatial sampling cover within that island. In each sampling site, bats were surveyed during three consecutive nights using one AudioMoth® v1.0.0 detector (López‐Baucells et al., 2021). This is an open‐source, programmable device capable of recording animal calls up to 384 kHz (Hill et al., 2018).…”

“…The recent increase in the availability of affordable autonomous recorders is making Passive Acoustic Monitoring a useful technique to undertake biodiversity surveys, allowing higher spatial and temporal replication (Hill et al., 2018; López‐Baucells et al., 2021). This is especially relevant for surveys of aerial insectivorous bats that commonly evade capture (Gibb et al., 2019), further allowing us to improve our understanding of the impacts of habitat loss and fragmentation on this diverse group of mammals.…”

Edge effects and vertical stratification of aerial insectivorous bats across the interface of primary-secondary Amazonian rainforest

“…These studies suggest bats may be affected by edge effects up to 3 km from the habitat boundary [22], with most studies indicating species richness declines at the forest edge, whereas the abundance of several dominant generalist species increases [13,42]. Aerial insectivores, which represent a large fraction of Amazonian bat diversity [43], have so far been overlooked. There have also been limited studies investigating how fragmentation and edge effects may affect bats differently between forest strata [but see [43][44][45].…”

“…Aerial insectivores, which represent a large fraction of Amazonian bat diversity [43], have so far been overlooked. There have also been limited studies investigating how fragmentation and edge effects may affect bats differently between forest strata [but see [43][44][45]. It is widely accepted that there are differences in both bat diversity and abundances between the canopy and understory in the Amazon [46,47].…”

The sound of restored soil: Measuring soil biodiversity in a forest restoration chronosequence with ecoacoustics

“…In recent years, ecoacoustics has been applied to monitor elusive species in several environmental contexts—particularly in conservation biology (Teixeira et al 2019; Stowell and Sueur 2020). For instance, passive acoustic monitoring (often shortened to ‘PAM’), which involves deploying autonomous acoustic sensors, has been used to collect recordings of biological sounds (known as ‘biophony’) from bats (Hintze et al 2021; López-Baucells et al 2021), birds (Abrahams 2019; Abrahams and Geary 2021), and invertebrates (Harvey et al 2011; van der Mescht et al 2021; Mankin et al 2022) in terrestrial environments; and cetaceans (Jones et al 2020; Guidi et al 2021), amphibians (Gan et al 2020), crustaceans (Kühn et al 2022), and fish (Popper and Hawkins 2019) in aquatic environments. Indeed, ecoacoustics has emerged as an efficient tool to measure and monitor biodiversity and has the potential to enhance the toolbox of restoration ecologists.…”