Bottlenose Dolphins Retain Individual Vocal Labels in Multi-level Alliances

Abstract

Cooperation between allied individuals and groups is ubiquitous in human societies, and vocal communication is known to play a key role in facilitating such complex human behaviors [1, 2]. In fact, complex communication may be a feature of the kind of social cognition required for the formation of social alliances, facilitating both partner choice and the execution of coordinated behaviors [3]. As such, a compelling avenue for investigation is what role flexible communication systems play in the formation and maintenance of cooperative partnerships in other alliance-forming animals. Male bottlenose dolphins in some populations form complex multi-level alliances, where individuals cooperate in the pursuit and defense of an important resource: access to females [4]. These strong relationships can last for decades and are critical to each male's reproductive success [4]. Convergent vocal accommodation is used to signal social proximity to a partner or social group in many taxa [5, 6], and it has long been thought that allied male dolphins also converge onto a shared signal to broadcast alliance identity [5-8]. Here, we combine a decade of data on social interactions with dyadic relatedness estimates to show that male dolphins that form multi-level alliances in an open social network retain individual vocal labels that are distinct from those of their allies. Our results differ from earlier reports of signature whistle convergence among males that form stable alliance pairs. Instead, they suggest that individual vocal labels play a central role in the maintenance of differentiated relationships within complex nested alliances.

Vocal behaviour of allied male dolphins during cooperative mate guarding

“…Signature whistles, i.e. individual identity signals, comprised approximately 28% of all whistles recorded (signature whistles identified in King et al 2018). This is a conservative estimate as the signature whistles of some of the focal males are yet to be identified.…”

“…Our hydrophone array consisted of four HTI-96 MIN series (flat frequency response: 0.002–30 kHz ± 1 dB) towed at 1 m depth around our research vessel in a rectangular formation (ca. 2 × 3.5 m), as per that outlined in King et al (2018). Recordings were made onto a TASCAM DR-680 MKII multi-track recorder at a sampling rate of 96 kHz.…”

“…Bottlenose dolphins possess a flexible communication system due to their propensity for vocal production learning, a notably rare skill in mammals (Janik 2014). Allied male dolphins in this population use signature whistles to broadcast individual identity (King et al 2018). During consortships, they frequently use a purported threat vocalisation called ‘pops’ (Connor and Smolker 1996; Vollmer et al 2015).…”

Bottlenose dolphins can understand their partner's role in a cooperative task

“…Indeed, motor synchrony between allied male dolphins is remarkably precise, with synchronous behaviours separated by just 130 ms [ 39 ]. Such synchrony is thought to promote both coordination and cooperation between alliance partners [ 50 ]. Our results, therefore, suggest that the tight behavioural coordination which bottlenose dolphins show in the wild may be a generalized cognitive ability that they can also apply to novel, albeit artificially constructed, cooperative situations.…”

The Origins of Self

“…This type of labelling has only been reliably identified in one species of dolphin (Tursiops truncatus) so far: it appears that every dolphin in a pod has a signature whistle (Cook et al 2004), and they each use that whistle to indicate their presence and position to other pod members. This signature whistle remains the same when the dolphin moves to a new group (which they do often), so it is a label the dolphin uses to identify themself, not a label given to the dolphin by each group (King et al 2018). Even more interestingly, they also use the signature whistles of other pod members to attract the attention of those others.…”