Bats play crucial roles in ecosystems, are increasingly used as bio-indicators and are an important component of tropical diversity. Ecological studies and conservation-oriented monitoring of bats in the tropics benefit from published libraries of echolocation calls, which are not readily available for many tropical ecosystems. Here, we present the echolocation calls of 15 species from the Valparai plateau in the Anamalai Hills, southern Western Ghats of India: three rhinolophids (Rhinolophus beddomei, R. rouxii (indorouxii), R. lepidus), one hipposiderid (Hipposideros pomona), nine vespertilionids (Barbastella leucomelas darjelingensis, Hesperoptenus tickelli, Miniopterus fuliginosus, M. pusillus, Myotis horsfieldii, M. montivagus, Pipistrellus ceylonicus, Scotophilus heathii, S. kuhlii), one pteropodid (Rousettus leschenaultii) and one megadermatid (Megaderma spasma). Discriminant function analyses using leave-one-out cross validation classified bats producing calls with a strong constant frequency (CF) component with 100% success and bats producing frequency modulated (FM) calls with 90% success. For five species, we report their echolocation calls for the first time, and we present call frequencies for some species that differ from those published from other parts of the species' ranges. This exemplifies the need for more local call libraries from tropical regions to be collected and published in order to record endemic species and accurately identify species whose calls vary biogeographically.
Bats are the second most species rich order of mammals, with great ecological diversity, especially in the tropics. They undertake a range of ecosystem services, including seed dispersal, pollination and insect control. A variety of ecologically and commercially important plants rely on bats to some degree as pollinators or seed dispersers (Kunz et al, 2011). Bats are also increasingly used as bioindicators to assess the biodiversity potential of areas and monitor environmental changes (Fenton et al., 1992; Jones et al., 2009; Pedersen et al., 2012), and there is therefore a need for reliable methods for studying bat assemblages.
For many parts of the tropics we lack even the most basic information on the abundance of different bat species, their distribution and habitat requirements. The development of comprehensive survey and monitoring methods is therefore critical for understanding the current status of bats and allowing future monitoring of populations (MacSwiney et al., 2008). The two main methods used for the study of bats are capturing them with mist nets and/or harp traps, or recording their echolocation calls using ultrasound detectors. The use of ultrasound detectors in the tropics has been hampered by the lack of reliable call libraries, which allow identification of bats to genus or species level from their echolocation calls.
Handling bats directly usually allows better species identification than acoustic methods, although some cryptic species are more easily separated by calls (Fenton, 1999), and allows the collection of useful data on the individual bat. However, it is also time-consuming and invasive. Further, it can also lead to biases in sampling as many species fly high above nets, are more agile or are better at detecting nets than others (O'Farrell and Gannon, 1999; Larsen et al., 2007). Habitats such as open fields, large water bodies or tall canopies cannot be easily or effectively sampled using capture methods.
Ultrasound detectors can be used in areas difficult to sample by capture methods, and detect foraging guilds that catching rarely does (Fenton, 1990; MacSwiney et al., 2008). Acoustic transects are easy to standardize and are thus useful for long-term monitoring. However, some species cannot yet be distinguished acoustically, and low intensity echolocators and non-echolocating bats are not accurately represented, particularly in cluttered habitats (Adams et al., 2012). Higher frequency echolocation calls attenuate quickly so are underrepresented; and the type of detector used can also affect which frequencies are recorded, and from what distance (Adams et al., 2012). Ultrasound detectors and catching in combination typically give the most complete inventories and thus they should be used together for surveying and monitoring (Murray et al., 1999; O'Farrell and Gannon, 1999; MacSwiney et al., 2008; Furey et al., 2009).
Given the advantages that ultrasound detectors bring to the study of bats, there have been increased efforts to build call libraries for more regions, especially those facing the gravest threats from habitat loss and conversion (Sedlock, 2001; Furey et al., 2009; Hughes et al., 2010, 2011). Recording calls from as many different localities as possible is important; new species will be identified and recorded, and biogeographic variation in calls can be assessed (Russo et al., 2007; Hughes et al., 2010).
We have started to build an echolocation call library to anal