The newly described Araguaian river dolphins, Inia araguaiaensis (Cetartiodactyla, Iniidae), produce a diverse repertoire of acoustic signals.

Gabriel Melo-Santos,Rodrigo Hipólito Tardin,Miriam Marmontel,Laura Johanna May-Collado,Israel De Sá Maciel,Angélica Lúcia Figueiredo Rodrigues,Maria Luisa Da Silva

doi:10.7717/peerj.6670

Abstract

The recent discovery of the Araguaian river dolphin (Inia araguaiaensis) highlights how little we know about the diversity and biology of river dolphins. In this study, we described the acoustic repertoire of this newly discovered species in concert with their behaviour. We analysed frequency contours of 727 signals (sampled at 10 ms temporal resolution). These contours were analyzed using an adaptive resonance theory neural network combined with dynamic time-warping (ARTwarp). Using a critical similarity value of 96%, frequency contours were categorized into 237 sound-types. The most common types were emitted when calves were present suggesting a key role in mother-calf communication. Our findings show that the acoustic repertoire of river dolphins is far from simple. Furthermore, the calls described here are similar in acoustic structure to those produced by social delphinids, such as orcas and pilot whales. Uncovering the context in which these signals are produced may help understand the social structure of this species and contribute to our understanding of the evolution of acoustic communication in whales.

Highlights

Compared to their marine counterparts, sounds produced by river dolphins and their role in communication remain understudied. Mizue, Nishiwaki & Takemura (1971)How to cite this article Melo-Santos G, Figueiredo Rodrigues AL, Tardin RH, de Sá Maciel I, Marmontel M, Da Silva ML, MayCollado LJ. 2019
A major constraint in studying river dolphins is that they do not typically perform conspicuous surface displays, making it especially difficult to identify individuals in the field (Best & Da Silva, 1989; Best & Da Silva, 1993; Brownell & Herald, 1972; Cassens et al, 2000; Crespo, Harris & González, 1998; Da Silva, 2009; Hamilton et al, 2001; Leatherwoods & Reeves, 1994; Reeves & Martin, 2009; Zhou, 2009). To overcome these challenges we aimed to study the acoustic repertoire of free-ranging Arauguaian botos (Hrbek et al, 2014) that regularly visit a fish market in Mocajuba in Northern Brazil (Dos Santos et al, 2014; Rodrigues et al, 2019)
Our results show that the Araguaian river dolphin has a more diverse acoustic repertoire than previously documented for the genus Inia (Amorim et al, 2016; Caldwell, Caldwell & Evans, 1966; Diazgranados & Trujillo, 2002; May-Collado & Wartzok, 2007; Ding, Würsig & Evans, 1995; Ding, Würsig & Leatherwoods, 2001; Kamminga et al, 1993; Podos, Da Silva & Rossi-Santos, 2002)

Summary

Introduction

Compared to their marine counterparts, sounds produced by river dolphins and their role in communication remain understudied. Mizue, Nishiwaki & Takemura (1971)How to cite this article Melo-Santos G, Figueiredo Rodrigues AL, Tardin RH, de Sá Maciel I, Marmontel M, Da Silva ML, MayCollado LJ. 2019. Compared to their marine counterparts, sounds produced by river dolphins and their role in communication remain understudied. In the Chinese river dolphin, the baiji (Lipotes vexillifer), whistles are thought to be the only communicative sounds produced by the species (Wang, Wenxiang & Zhifan, 1995; Wang, Wang & Akamatsu, 1999; Wang et al, 2006; Xiao & Jing, 1989). The Baiji whistles are lower in frequency (5–6 kHz), less modulated, and produced more infrequently than delphinid whistles (Wang, Wenxiang & Zhifan, 1995; Wang, Wang & Akamatsu, 1999; Wang et al, 2006; Xiao & Jing, 1989). The social sounds of the Franciscana (Pontoporia blainvillei) involved the emission of whistles (1.6–94.6 kHz) as well as burst pulses (Cremer et al, 2017)

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