Bing Xie:
Exploring links between vocalisations and social dynamics - the case of the plains zebra (Equus quagga)

Acoustic signals play vital roles in social life, exhibiting far-reaching abilities for long-distance communication or short-range functions within groups. However, the link between acoustic signals and social life still remains to be explored in many species, particularly in the context of social dynamics in wild species. The plains zebras (Equus quagga) provide an ideal model for studying this topic due to their loud vocalisations and complex social societies.

This thesis investigates the relationships between acoustic signals and social dynamics in this species. Firstly, a literature review was conducted, summarising the connections between acoustic signals and collective movement, separation risk and cohesion maintenance, fission-fusion dynamics, and social network analysis. Secondly, the vocal repertoire of plains zebras was examined using supervised and unsupervised learning methods applied to both acoustic features and spectrograms, resulting in the identification of four distinct call types: snorts, soft snorts, squeals, and whinnies. Moreover, the individual distinctiveness of these call types was explored, revealing that snorts contained individual information to a larger extent than squeals. Thirdly, social network analysis was applied to squeals and social interactions, and links between the resulting networks were explored. The analysis revealed that squeals are often produced during responsive, agonistic, visible and non-physical interactions.

Lastly, snorts were analysed along with visual signals to determine their role in decision-making processes underlying collective movement departures. The results showed that zebras display a partially shared decision-making process, involving all individual roles (initiators, followers, and non-followers) rather than just initiators. Additionally, snorts appeared to have less influence on the decision-making process compared to visual signals. Overall, this thesis establishes a solid foundation for studying zebra acoustic communications and social lives. It contributes to further comprehensive explorations into the links between acoustic signals and social dynamics.