Beyond mating calls: unveiling the acoustic complexity in an endangered foam-nesting frog of north-eastern Brazil

Vocal communication in anurans varies from simple to complex repertoires, with some species using a single call type across social contexts, while others produce distinct calls for reproductive, aggressive, or defensive interactions. Despite its importance for understanding acoustic signal evolution, the full extent of vocal complexity remains poorly known for many species. Here, we describe the acoustic repertoire of Physalaemus caete, an endangered foam-nesting frog endemic to the northern Brazilian Atlantic Forest. From recordings of 24 males, we identified eight call types grouped into six behavioural subcategories. Some calls involved in social interactions exhibited non-linear phenomena (NLPs). Multivariate analyses revealed significant acoustic differences between calls with and without NLPs, with spectral parameters accounting for most of the differences between calls. Principal Component Analysis supported the separation of calls by behavioural context, with emphasis on spectral variables, while cluster analysis indicated moderate similarity between certain reproductive and aggressive calls. Coefficients of variation suggested that call rate, fundamental and dominant frequencies, and emphasised harmonics may contribute to individual recognition, although these traits were influenced by temperature and body size. These findings highlight the vocal complexity of P. caete and provide a foundation for future passive acoustic monitoring efforts for this threatened species.