Enhancing sampling design in mist-net bat surveys by accounting for sample size optimization

Trophic structure and foraging strategies in a bat community in northern Pantanal, Brazil

The influence of the landscape mosaic on the composition of the bat fauna regarding its trophic guild in a ranch area of northern Pantanal was evaluated. Seven trophic categories and five foraging strategies were found, composing 11 guild associations. Cluster analysis and non-metric multidimensional scaling (NMDS) revealed the structure of the data and enabled a broader understanding of resource exploitation. The similarity between sites for the presence of guilds was moderate, with the presence of aerial insectivores and trawling insectivores occurring in most of them, mainly in pasture areas and in the cambará forest. Gleaning sedentary frugivores, gleaning nomadic frugivores, and gleaning nectarivores were present in almost all sites, most often in dense acuri palm forest. Frugivores were the most numerous at the individual level, followed by trawling insectivores and hematophagous. The similarities between groups ranged from low to moderate. Some subgroups identified in the analyzes showed high similarity, with strong congruences between sites. The areas used by cattle do not seem to restrict the use by some species of bats, especially those already proven to be associated with degraded areas. However, information is still lacking to predict which level of alteration is acceptable for the conservation of each guild and foraging strategy of bat species.

Bats from the Pedra Branca Forest, Rio de Janeiro, Brazil

The Pedra Branca Forest is located in a highly-urbanised region of the central portion of Rio de Janeiro City, comprises the largest urban forest on the continent and is isolated from other Atlantic Forest remnants. The local flora and fauna are protected by three conservation units (Pedra Branca State Park, Prainha Municipal Natural Park and Guaratiba State Biological Reserve) and one biological station (Fiocruz Atlantic Forest Biological Station—EFMA). Here, we provide an updated list of the bat fauna for the remnant. The results are based on samplings at EFMA and literature data from Pedra Branca State Park and Prainha Natural Park. The three sampling sites combined resulted in 31 species, 23 genera and four families. Phyllostomidae was the richest family with 24 species, followed by Vespertilionidae with five species (3%) and Molossidae and Noctilionidae with one species. The local bat fauna was predominantly composed of species with a broad geographic distribution.

Are bat mist nets ideal for capturing bats? From ultrathin to bird nets, a field test

The use of mist nets is the most widespread technique to capture bats; however, no study has compared if the type of ground-level mist net used during sampling affects bat captures. We sampled bats using three different types of mist nets that varied in mesh (16, 18, and 20 mm) and denier/ply (45/1 and 75/2) sizes over 76 half-night surveys. We used 17–20 mist nets and checked them at intervals of 15–20 min. Capture rate for echolocating bats was higher in the two mist nets with the biggest denier/ply and smaller mesh sizes. “Ultrathin bat mist nets” showed the lowest capture rates (1.5 times less than “Regular bat mist nets”), whereas “Bird mist nets” had capture rates only 1.2 times smaller than “Regular bat mist nets.” Our results showed that “Bird mist nets” can sample echolocating bats almost as well as “Regular bat mist nets,” and that thinner mist nets may not be the best solution to capture bats that echolocate at high frequencies in this type of surveys. We highlight the importance of considering the efficiency, durability, and longevity of mist nets when choosing the ideal mist-net type for a bat survey.

Optimizing bat bioacoustic surveys in human-modified Neotropical landscapes

During the last decades, the use of bioacoustics as a non-invasive and cost-effective 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.

Drivers of bat roles in Neotropical seed dispersal networks: abundance is more important than functional traits

While functional traits can facilitate or constrain interactions between pair of species in ecological communities, relative abundances regulate the probabilities of encounter among individuals. However, the relative importance of traits and relative abundances for the role species play in seed dispersion networks remains poorly explored. Here, we analyzed 20 Neotropical seed dispersal networks distributed from Mexico to southeastern Brazil to evaluate how relative abundance and functional traits influence bat species' roles in seed dispersal networks. We tested how bat relative abundance and traits relate to species contribution to between-module (c metric) and within-module connectivity (z metric) and their position and potential to mediate indirect effects between species (betweenness centrality). Our results indicate that relative abundance is the main determinant of the role bats play in the networks, while traits such as aspect ratio show modest yet statistically significant importance in predicting specific roles. Moreover, all seed dispersal networks presented two or three superabundant obligatory frugivore species that interacted with a high number of plants. The modest influence of the functional traits on species' roles is likely related to the low variation of morphological traits related to foraging ecology, which reduces the chances of morphological mismatching between consumers and resources in the system. In this scenario, abundant bats have higher chances of encountering resources and being capable of consuming them which leads such species to play critical roles in the community by acting as module hubs and network connectors.