Interview with a rhino : how vocalisations reflect social interactions in the captive southern white rhinoceros (Ceratotherium simum simum)
White rhinoceroses (WR) are one of Africa’s most endangered mammals and highly reliant on successful captivity breeding. Regrettably, these semi-social megaherbivores often reproduce only laboriously in captivity. Deficiency in socio-sexual behavioural patterns and unsuitable group composition are currently discussed as potential causes and raise the question of how these conditions can be monitored noninvasively. Bio-acoustic methods were currently investigated for animal welfare monitoring, as vocalisations are discussed to be indicators for social interferences and individual condition. Therefore, this study aims to examine the function of vocalisations in WR regarding socio-sexual behaviour and the quality of social interactions between group members. Behaviour and vocalisations of 32 Southern white rhinoceroses (Ceratotherium simum simum) were video- and audio recorded in seven European zoos using focal animal sampling. Vocal analysis focused on the three predominant call types: pants, threats and snorts. In order to clarify their function in social interactions, the context in which each call type was uttered and the respective receiver of the call were determined. The results show that the three call types have distinct functions. Pants are mainly uttered in affiliative interactions by males while approaching the females. Threats are mainly uttered by females towards males during agonistic interactions to displace the bull. Snorts are uttered by all individuals equally during various positive relieved contexts such as resting, feeding and affiliative interactions but not during agonistic interactions. It can be concluded that the three call types can be used to monitor sexual behaviour (pants) as well as the social quality of group composition (threats, snorts). Thus, in order to address the animals’ natural requirements in captivity, attention should not only be paid to obvious signs of behavioural anomalies (e.g. stereotyped movements, escalated fights, health impairments), but also to vocalisation that can serve as a bio-acoustic tool for animal management.