Abstract
Bats are the most diverse mammalian order, second to rodents, with 1400+ species found globally across almost every continent. In the tropics, where it is possible to find more than 60 bat species at a single site, they are heavily impacted by fire, deforestation, and land use change. The island of Borneo is a biodiversity hotspot, yet it is undergoing severe deforestation, driven by plantation palm oil and logging. Despite this, the small sultanate of Brunei Darussalam still has approximately 54% coverage of unlogged forest. Monitoring bats is challenging due to their small size, ability to y, cryptic nature and nocturnal activity. More recently, bioacoustic techniques are being incorporated into bat research methods. Either through the use of acoustic bat lures, or by utilising passive acoustic monitoring (PAM) techniques. Acoustic bat lures have been developed on the premise that broadcasting an acoustic stimuli can increase the number of bat captures in mist nets or harp traps. However, this is still a relatively new, niche method, with just 9 published studies on their use. A questionnaire of 27 questions, circulated widely by numerous NGO's and available online for two months, was used to gather information from lure users globally. Results indicated there are ethical and practical concerns surrounding their use, with a myriad of methods, broadcast calls, target species, and projects incorporating lures. Despite general success with acoustic bat lures in the literature, the effect of lures, which will likely always be species-specific, is yet to be fully understood. This raises questions regarding the appropriate use of these lure devices, particularly with a lack of international guidelines.
Field tests comparing different lure devices and broadcast calls in Brunei Darussalam over two consecutive years, totalling 55 `trapping nights', showed increased captures in traps with a lure. Particularly for Kerivoula spp. and Murina spp., whilst Rhinolophus spp. were deterred from traps. Statistically, there was no difference in capture rates between the two lure devices (Sussex Autobat and Apodemus Batlure), or the broadcast calls used. These results highlight the species-specific effects of lures. Diversity estimators Chao 1 & ACE indicate that short-term community surveys are insufficient to assess the full diversity of this region. However, including a variety of trapping sites/traps, and potentially incorporating a lure (being aware of species-specific responses), will likely assist future efforts. Furthermore, PAM is becoming widely used
to study bat populations, although it is still in its infancy in the tropics, and requires a baseline call library. Reference calls were recorded on an Anabat Walkabout bat detector upon release of 40 individual bats across 14 species and 6 genera. Principal Component Analysis of 339 pulses showed considerable overlap in call structure of frequency modulated (FM) bat calls, although constant frequency (CF) bat calls are distinguishable to species level. Kerivoula papiliosa, Kerivoula lenis, and Myotis spp., which are often difficult to distinguish morphologically, could potentially be identified using bioacoustic methods. This reference call library and preliminary analysis is an initial step towards developing an acoustic classifier for the bats of Brunei, and call recordings are being incorporated into a broad acoustic classifier for the bats of Borneo.