Complementarity between mist-netting and low-cost acoustic recorders to sample bats in Amazonian rainforests and savannahs

Abstract

Effective survey methods are paramount to measure changes in species distribution, populations dynamics and to guide conservation. Mist-netting and passive acoustic monitoring are two of the most used techniques to sample bats assemblages. Yet, despite the great potential of low-cost autonomous ultrasound recorders in surveying bat assemblages, we lack thorough assessments of their performance in relation to more established survey methods.Taking advantage of the rich bat fauna of the north-eastern Brazilian Amazon, we set out to i) investigate the complementarity of mist-netting and acoustic surveys in sampling bats in forest and savannah habitats in the Savannahs of Amapá, and ii) undertake a cost-effectiveness evaluation of using one, two or three recorders per sampling site to simultaneously survey bat assemblages. The two methods show complementary, and overall species diversity recorded with mist nets was higher than with acoustic recorders. However, species diversity was higher with acoustic recorders than with mist nets when considering a reduced (n < 3) number of transects.In addition, we found a gain in species diversity when using more than one acoustic recorder in forest habitats, despite the low cost-effectiveness. However, there were no differences between the diversity using one, two or three acoustic recorders in savannah. Due to possible device malfunction, we recommend the use of at least two acoustic recorders in both habitats to reduce the likelihood of data loss. The use of low-cost bioacoustic recorders in bat surveys can help to address critical knowledge gaps for poorly known aerial-hawking insectivores and support evidence-based conservation strategies.

Global systematic map of research on bats in agricultural systems

“…Using exclusively one of these methods can lead to sampling bias, as acoustic recordings perform better at recording insectivorous bats that echolocate, while mist nets are a more effective method for capturing bats that are unable to avoid interception traps (MacSwiney-G et al, 2008;Yoh et al, FIGURE 4 Distribution of studies published worldwide in which bats were sampled in agricultural systems or that evaluate the effect of these agricultural systems on bats, according to the sampling methods. 2020; Appel et al, 2021;Carvalho et al, 2023). Ultimately, this can lead to an incorrect interpretation of the results found.…”

“…For example, Heer et al (2015) compared forest fragments with rubber-cacao plantations and found that the species richness recorded with acoustics did not differ between these habitats, while the number of species was higher in forest fragments when considering only the species sampled with mist nets. Thus, an approach combining several sampling methods, such as mist nets and acoustic recorders, would be ideal to reduce the risk of sampling bias for certain bat groups and, thus, gain a better understanding of their response to replacement of natural areas with agricultural systems (MacSwiney-G et al, 2008;Appel et al, 2021;Carvalho et al, 2023). Another option would be to combine mist nets with harp-traps or with captures in roost (e.g., Flaquer et al, 2007;Pech-Canche et al, 2011;Xavier et al, 2018;Appel et al, 2021).…”

Optimal inventorying and monitoring of taxonomic, phylogenetic and functional diversity

“…Mist nets and acoustic recorders are the most used and efficient methods for sampling bats [ 38 ]. However, each of these methods is biased toward different families within Chiroptera; Phyllostomidae bats being more captured by mist nets and aerial insectivorous bats (e.g., Vespertilionidae and Molossidae) being more recorded using acoustic recorders [ 38 , 39 ]. Therefore, to inventory or monitor the order Chiroptera, these two methods are considered complementary [ 39 , 40 ] and we used both in a landscape composed of savannahs and forest patches in Northeastern Amazon.…”

Secondary forest buffers the effects of fragmentation on aerial insectivorous bat species following 30 years of passive forest restoration

“…In Brazil, they account for nearly half (48%) of the greater than 181 described bat species (Garbino et al 2022). They are best sampled with acoustic methods, as their highly developed echolocation means that, unlike their phyllostomid counterparts, they are rarely captured in mist nets (Appel et al 2021 a ; Carvalho et al 2023). The sensitivity of aerial insectivorous bats to forest fragmentation is largely mediated by their wing morphology and echolocation (Bader et al 2015; Colombo et al 2023) which can determine foraging success within a habitat based on the level of clutter (Schnitzler & Kalko 2001).…”