Similar to Discoglossus (Weber, 1974; Glaw and Vences, 1991; Vences and Glaw, 1996), the calls heard from L. nigriventer were of very low intensity, low spectral frequency, and consisting of a presumed expiratory and a presumed inspiratory note. As the release calls of handled L. nigriventer sound very similar to the recorded calls, we assume the calls to be uttered at the water surface like in Discoglossus species. While we cannot exclude that other, more intense call types can be emitted by this species, the absence of externally visible vocal sacs in males makes it likely that their vocalisations mainly serve short-distance communication. Although we could only achieve provisional recordings under suboptimal conditions in captivity, which might have distorted some of the call features, we were able to record the calls of several male L. nigriventer individuals. Air temperature during recordings varied between 13.5–18 °C and water temperature between 14–15 °C. As several males were kept together in the same aquarium, the following descriptive statistics refer to calls of various males in unknown proportions.
Calls were mostly uttered in a series and were separated from each other by short intervals of silence varying from 246–1606 ms (mean + SD: 787 + 609 ms; N = 65). Each call consisted of two notes which we assume represent sounds produced by expiration (first note) followed by inspiration of air into the lungs (second note). Both notes were spectrally structured and pulsatile, but a clear distinction and count of pulses was not possible. The two notes of one call were not separated by a silent interval or distinct decrease in amplitude. Therefore, in the spectrogram the two notes are mostly recognisable by the somewhat lower frequency and higher intensity of the second (inspiratory) note (Fig. 8). Dominant frequency peak averaged over the total call (mean + SD) was 775.5 + 80 Hz (N = 72); frequency range was roughly between 0–1500 Hz. Call duration (N = 72) ranged between 725–1212 ms, with the expiratory note being longer (671 + 115 ms) than the inspiratory note (291 + 28 ms) (Table 3).