Social drivers of signature whistle complexity in bottlenose dolphins (Tursiops aduncus)

Abstract

Darwin theorised that highly social animals experience a greater need to mediate their social interactions through complex communication. This idea forms the ‘Social Complexity Hypothesis for Communication Complexity’ (SCHCC), where highly social groups require more complex communication to regulate interactions and relationships. One way to introduce complexity to a communication system is vocal production learning; where animals learn to create a new signal or modify one from their repertoire. Bottlenose dolphins (Tursiops sp.) use vocal production learning to create individually distinct signature whistles that broadcast their identity. Signature whistles are formed within the first few months of life and are primarily used as contact calls. As per the SCHCC, this complex communication system has coevolved alongside a highly complex social system. Male bottlenose dolphins in Shark Bay, Western Australia form multi-level alliances, where three orders of alliances will cooperate to herd oestrus females and defend them from rival alliances. Here, I examine whether social network size drives the complexity of signature whistle frequency modulation in this population. Using long-term social network data from 20 male dolphins, I found no relationship between social network size and signature whistle complexity (lm estimate=0.001, t=1.04, p=0.30). However, one male engaged in a solitary foraging specialisation (sponging), resulting in a significantly smaller social network size compared to non-sponging dolphins. After removing this outlier, there was a non-significant positive trend indicating that increased social network size predicts signature whistle complexity (lm estimate=0.003, t=1.83, p=0.08). Calves in highly social environments will be exposed to many different whistle types, thus more complex whistle structures are likely to be adopted to allow individuals to differentiate themselves from conspecifics. It is possible that environmental factors also drive whistle complexity, where individuals living in complex physical or ecological environments will adopt frequency modulation patterns that maximise sound transmission.

Date of Award	25 Jan 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Andrew N Radford (Supervisor) & Stephanie L King (Supervisor)