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Bioacoustics, 2015 http://dx.doi.org/10.1080/09524622.2015.1076347 Quantitative description of the vocal repertoire of the territorial olive frog Babina adenopleura from Taiwan Ming-Feng Chuanga, Yeong-Choy Kama* and Mark A. Beeb aDepartment of Life Science, Tunghai University, 1727 Taiwan Boulevard, Taichung 40704, Taiwan; bDepartment of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108, USA (Received 22 May 2015; accepted 20 July 2015) Anurans communicate using a repertoire of acoustic signals that can be classified as different call types based on differences in both their acoustic properties and the contexts in which they are produced. Descriptions of these repertoires represent a key first step towards understanding the vocal behaviour of any species and provide a critical foundation for comparative bioacoustic studies. In this study of the olive frog, Babina (formerly Rana) adenopleura, a territorial species from subtropical Taiwan, we used focal observations, acoustic recordings and statistical analyses of temporal, spectral and amplitude-related call properties to describe six different call types in the species’ vocal repertoire. These call types included a putative advertisement call, territorial call, encounter call, amplectant call, distress call and alarm call. Advertisement calls consisted of four to five discrete notes, and they were the most commonly produced call. Territorial and encounter calls were delivered during interactions with other males; the former is a two-note call, whereas the latter is a distinctly pulsatile signal. Amplectant calls were acoustically similar to territorial calls but were delivered while males were in amplexus. Distress calls were given while the animal was being consumed by a snake, and alarm calls were recorded in response to startling stimuli. With basic descriptions of these call types in hand, we discuss several testable hypotheses for their putative adaptive functions. Keywords: amphibian; behaviour; communication; Lien-Hua-Chih research center Introduction Most anuran amphibians use vocal signals to convey information during social and reproductive interactions (Gerhardt and Huber 2002; Wells and Schwartz 2006; Wells 2007). Although male frogs are more often the signallers, both male and female frogs benefit from receiving and responding to signals. Frog calls can inform potential receivers about a signaller’s species identity (Blair 1955; Littlejohn 1965), body size and fighting ability (Davies and Halliday 1978; Wagner 1992; Bee et al. 1999), individual identity (Bee and Gerhardt 2001a, 2001b; Bee et al. 2001; Gasser et al. 2009), genetic quality (Welch et al. 1998), distance (Wilczynski and Brenowitz 1988; Marshall et al. 2003), and its position in azimuth (Klump and Gerhardt 1989, Caldwell and Bee 2014) and elevation (Gerhardt and Rheinlaender 1982). Quite commonly, male frogs produce a repertoire of vocalizations consisting of two or more acoustically distinct call types used in different contexts (Bogert 1960; Duellman and Trueb 1986; Wells 2007; Toledo et al. 2014). ‘Advertisement calls’ are the vocalization most often produced by male frogs (and most often studied by biologists). *Corresponding author. Email: [email protected] q 2015 Taylor & Francis 2 M.-F. Chuang et al. They are used both to announce possession of a territory or calling site to rival males and to attract sexually responsive females (Wells 1977b). Males, and sometimes females, also use ‘courtship calls’ during close-range reproductive interactions (Wells 1980, 2007). Calls that males give while in amplexus have been termed ‘amplectant calls’ and may function to stimulate oviposition (Odendaal et al. 1983). Males may also produce one or more distinct call types used primarily or exclusively in aggressive contexts (Hutter et al. 2013). For example, ‘territorial calls’ may be relatively long-range signals to other males that function in maintaining minimum inter-male spacing. ‘Encounter calls’ are also directed towards rival males, usually in more close-range interactions that may also involve physical aggression. Both sexes of frogs also commonly produce vocalizations during encounters with predators or in response to startling stimuli that have variously been termed ‘distress’, ‘alarm’ or ‘warning’ calls (Toledo et al. 2014). Although acoustic communication in frogs has been a topic of intensive research for several decades, we still know relatively little about the vocal repertoires used by most of the more than 6500 described species of frogs (Frost 2015). A better understanding of vocal repertoires across a greater range of species would facilitate further comparative studies of both the mechanisms and evolution of vocal behaviour in this group. Our objective in this study was to describe the vocal repertoire of males of the olive frog, Babina adenopleura (Ranidae). Common throughout China and Taiwan (Chuaynkern et al. 2010), the olive frog is a territorial species with a mating system best characterized as resource-defence polygyny. Territories function as oviposition sites, and individual males have been observed to defend the same territory for up to 43 consecutive nights (Chuang et al. 2013). Here, we report results from in-depth, within-individual quantitative analyses of putative advertisement calls, territorial calls and encounter calls. We also describe three additional call types – a putative amplectant call, distress call and alarm call – recorded opportunistically during the course of the study. Materials and methods Study site and subjects We recorded males of B. adenopleura between June and September of 2008 and 2009 at the Lien-Hua-Chih Research Center in central Taiwan. Our recordings were made in one of two locations approximately 600 m apart. One was a permanent pond (5 m £ 10 m, maximum depth of approximately 1 m) located in a natural forest (120852059.500E, 2385508.900N), and the second was in a flooded (,30 cm deep) palm farm where areca nuts (Areca catechu; also known as betel nuts) are grown and harvested (12085301200E, 2385500100N). Territorial males were abundant at both sites. After each recording, we captured unmarked males, measured their body size (SVL, snout-vent length, to the nearest 0.01 mm and mass to the nearest 0.05 g) and individually marked them using a numbered waistband. We released all animals at their site of capture within 10 to 30 min of capture. In total, we recorded 17 males having a mean (^SD here and throughout) SVL of 51.3 ^ 2.5 mm and mass of 12.8 ^ 1.9 g. Acoustic recordings and analyses All of our acoustic recordings were obtained using a Marantz PMD670 digital recorder (D&M Holdings Inc, Kanagawa, Japan) and a Sennheiser ME67/K6 directional microphone (Sennheiser Electronic GmbH & Co. KG, Hanover, Germany), which was mounted on a tripod and placed with its recording tip approximately 0.5 m in front of a focal male. Sounds Bioacoustics 3 were recorded at a sampling rate of 44.1 kHz with 16-bit resolution. At the completion of recordings, we measured the water temperature at the focal male’s calling site using a Tecpel DTM-3108 digital thermometer (0.18C accuracy). We measured water temperature because males called from the surface of the water. Across our recordings, water temperature varied over a narrow range between 22.48C and 24.88C(X ¼ 23.88C; N ¼ 24). We used Raven Pro v1.5 (Bioacoustics Research Program 2014) to analyse our recordings. In total, we analysed 420 vocalizations, including 280 advertisement calls (20 from each of 14 males), 50 territorial calls (1 to 8 calls from each of 14 males), 32 encounter calls (1 to 6 calls from each of 14 males), 45 amplectant calls (22 and 23 calls, respectively, from 2 males), 9 distress calls (from 1 male) and 4 alarm calls (1 call from each of 4 males). Waveforms and spectrogram of these different call types are presented in Figure 1. We focus most of our analyses on advertisement calls, territorial calls and encounter calls, because all three call types were recorded from the same sample of 14 individuals. Table 1 describes the 15 acoustic properties we measured for these 3 call types. In total, nine properties were measured using the entire call as the unit of measurement (Figure 2 (A)). Three temporal properties were measured for each call, including call duration, the number of sound elements (i.e. notes or pulses) per call and the element rate within a call. Preliminary analyses indicated that calls have a bimodal frequency spectrum with a prominent low-frequency peak and high-frequency peak (Figure 2(B)). Five spectral properties were measured for each call to characterize this spectrum, including low peak frequency, low peak harmonic number, high peak frequency, high peak harmonic number and the relative amplitude of the low and high peaks (Table 1; Figure 2(B)). In all advertisement, territorial and encounter calls, the low peak frequency was the second harmonic of a fundamental frequency that was either missing or significantly attenuated relative to the low and high peaks. This was confirmed by determining the fundamental frequency for a subset of calls as the reciprocal of the average period of the quasi-periodic fine-temporal waveform. All frequency measurements were based on 1024-point fast Fourier transforms and Hann windows and were made from the average power spectrum computed over the duration of a call (unless indicated otherwise below). We also measured the peak power of each call; however, we note that these values are only used for comparisons across call types from the same recording of the same individual because they do not represent independently calibrated measures of sound pressure level. As illustrated in Figure 2(A), three additional temporal properties were measured for each of two consecutive sound elements in each call (duration, rise time and fall time). For convenience, we designate these two elements as E1 and E2, noting that they could correspond to what are commonly referred to as ‘notes’ or ‘pulses’ in the literature, depending on the acoustic structure of the call itself.

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