Release and distress calls in European Spadefoot toads, genus Pelobates

The acoustic repertoire of most anurans, even common species, is still insufficiently known. Here, we present a thorough quantitative description of acoustic parameters in release and distress calls in the three European spadefoot toad species, genus Pelobates. We also explored the intra- and interspecific variation and effects of body size on acoustic traits. We analysed a total of 749 release calls of 34 individuals of Pelobates fuscus and P. syriacus, and 312 distress calls of 36 individuals of P. fuscus, P. syriacus and P. cultripes. Release calls consisted of a note with one to three initial pulses of lower energy and a group of consecutive pulses characterized by higher energy in both species analysed. The structure of the distress calls was similar in all three species: loud, explosive, cat meow-like, single multi-pulsed notes rich in harmonics. Some of the variation among species in acoustic parameters in the release and distress calls is related to body size. Acoustic properties for both release and distress calls showed high levels of variability in all species. This pattern of variation is different from what is regularly found in the more conservative advertisement calls, and we advocate that such high variability is possible because release and distress call are not signals with divergent evolutionary history among related species.