Towards a regional call library: Classifying calls of a species-rich bat assemblage in a Bornean karst rainforest

Acoustic monitoring with ultrasonic detectors has emerged, in recent years, as an essential tool to quantify the activity of echolocating, insectivorous bats and identify critical commuting and foraging habitats. Comprehensive reference call libraries are critical for the identification of species from their calls. This is especially important in species diverse areas like Gunung Mulu National Park (Sarawak). This study aims to (1) develop a call library for all known echolocating bat species found in Gunung Mulu National Park, (2) determine if calls of different species can be automatically classified using discriminant function analysis, and (3) examine intraspecific variation in relation to sex and geographical location, for calls in species of the families Rhinolophidae and Hipposideridae. Between 2012 and 2017, insectivorous bats were trapped within and outside the park. Echolocation calls were recorded from a total of 508 individuals, representing 31 species from 8 families. Results from discriminant function analysis indicated that the majority of cave roosting bats, which included Chaerephon plicatus, Miniopterus australis, Myotis horsfieldii and 13 species from the families Rhinolophidae, Hipposideridae, and Emballonuridae, could be readily distinguished from their calls, when manually separated into groups according to call structure. However, classification success was much lower for the remaining 15 species that consisted mainly of forest roosting bats from the family Vespertilionidae. This reference call library is expected to contribute to a regional online open-access database. It can be used to survey and monitor selected species in Gunung Mulu National Park as well as highlighting the importance of threatened habitats outside the boundary for these species.