Testing the effectiveness of surveying techniques in determining bat community composition within woodland

Abstract

Context: Determining the biodiversity of an area is essential for making targeted conservation decisions. Undertaking surveys to confirm species presence or to estimate population sizes can be difficult, particularly for elusive species. Bats are able to detect and avoid traps, making it difficult to quantify abundance. Although acoustic surveys using bat detectors are often used as a surrogate for relative abundance, the implicit assumption that there is a positive correlation between activity levels and abundance is rarely tested.  Aims: We assessed the effectiveness of surveying techniques (i.e. trapping and acoustic monitoring) for detecting species presence and tested the strength of collinearity among methods. In addition, we tested whether the use of an acoustic lure (a bat-call synthesiser) increased bat-capture rate and therefore species detectability.  Methods: Surveying was carried out over 3 years in central Scotland (UK), in 68 woodlands within predominantly agricultural or urban landscapes.  Key results: There was a significant positive relationship between bat activity recorded on ultrasonic detectors and the relative abundance of Pipistrellus pygmaeus and P. pipistrellus, but not those in the genus Myotis. In general, acoustic monitoring was more effective than trapping at determining species presence; however, to ensure rarer or quiet species are recorded, a complementary approach is required. Broadcasting four different types of echolocation call resulted in a 2–12-fold increase in trapping success across four species of insectivorous bat found in the study region. Whereas lure effectiveness remained unchanged for female P. pygmaeus over time, there was a marked increase in the number of males captured using the lure throughout the summer (May to September).  Conclusions: In the present study, we have demonstrated a variety of ways to increase surveying efficiency, which can maximise the knowledge of diversity in an area, minimise wildlife disturbance, and enhance surveying effectiveness. Implications:Increasing surveying efficiency can improve the accuracy of targeted conservation decisions.