Proximity-based vocal networks reveal social relationships in the Southern white rhinoceros

Abstract

Vocal communication networks can be linked to social behaviour, allowing a deeper understanding of social relationships among individuals. For this purpose, the description of vocal dyads is fundamental. In group-living species, this identification is based on behavioural indicators which require a high level of reactivity during social interactions. In the present study, we alternatively established a proximity-based approach to investigate whether sex-specific differences in vocal communication reflect social behaviour in a species with rather loose social associations and low levels of reactivity: the Southern white rhinoceros (Ceratotherium simum simum). We performed audio- and video recordings of 30 captive animals from seven groups. Vocal networks for the four most common call types were constructed by considering conspecifics at close distance (≤ 1 body length) to the sender as potential receivers. The analysis of the resulting unidirectional structures showed that not only the sex of the sender but also the sex of the potential receiver, the quality of social interactions (affiliative or agonistic) as well as association strength predict the intensity of vocal interactions between group members. Thus, a proximity-based approach can be used to construct vocal networks providing information about the social relationships of conspecifics—even in species with loose social associations where behavioural indicators are limited.

The female effect—how female receptivity influences faecal testosterone metabolite levels, socio-positive behaviour and vocalization in male Southern white rhinoceroses

“…Vocalizations that due to ambient noises could not be reliably assigned to a call type or a sender were excluded from the analysis. A previous study ( Jenikejew et al , 2020 ) on vocal communication structure in SWR had demonstrated sex-specific differences in call rates for the contact call Pant (including its call variation Hic) as well as the agonistic call Hiss, emphasizing a relevant role of these two call types for mating behaviour. A further analysis in the present study therefore only included Pant and Hiss calls.…”

“…Besides, a conspicuous variation of the Pant call, also known as Hic, has been described as specifically characteristic during courtship, particularly for free-ranging bulls ( Cinková and Policht, 2016 ; Cinková and Shrader, 2020 ). A recently described sex difference in Pant call rates additionally indicates a socio-sexual function of this call type, with adult bulls panting significantly more often than adult females ( Jenikejew et al , 2020 ). A similar sex-specific variation in call rates has been also identified for the Hiss ( Jenikejew et al , 2020 ), a call type associated with agonistic interactions ( Owen-Smith, 1973 ; Policht et al , 2008 ), with females calling significantly more often than males.…”

“…Throughout the recordings, vocalizations were detected by auditory identification and categorized according to the literature ( Owen-Smith, 1973 ; Policht et al , 2008 ; Linn et al , 2018 ). For each vocalization, the respective call type, sender as well as potential receiver were noted (see Jenikejew et al , 2020 for detailed description). Vocalizations that due to ambient noises could not be reliably assigned to a call type or a sender were excluded from the analysis.…”

Linking socio-sexual and vocal behaviour with faecal progesterone and oestrogen metabolite levels in Southern white rhinoceros females

“…Vocalizations were detected by auditory identification and categorized according to literature ( Cinková and Policht, 2014 ; Linn et al , 2018 ; Owen-Smith, 1973 ; Policht et al , 2008 ). For each vocalization, the respective call type, sender as well as potential receiver were noted (see Jenikejew et al , 2020 for a detailed description). Analysis focused on the contact call Pant and the agonistic call types Hiss and Grunt only, as a previous study demonstrated sex-specific differences in call rates, and hence a potentially relevant role in mating context for these call types ( Jenikejew et al , 2020 ).…”

Individual distinctiveness across call types of the southern white rhinoceros (Ceratotherium simum simum)

“…Given the poor eyesight of rhinoceroses, this more pronounced social organization may favor a more complex acoustic communication system. Indeed, acoustic signals play an essential role in the coordination of mother–infant interactions ( Linn et al 2018 ), during friendly encounters, during aggressive interactions ( Owen-Smith 1973 ; Policht et al 2008 ; Jenikejew et al 2020 ), and during mating behavior of southern white rhinoceroses ( Owen-Smith 1973 ; Cinková and Shrader 2020 ). For example, vocalizations play a very important role in coordinating male and female behavior during consortship ( Owen-Smith 1973 ) where bulls follow a single cow for 2–3 weeks.…”