Sperm whale codas may encode individuality as well as clan identity

Abstract

Sperm whales produce codas for communication that can be grouped into different types according to their temporal patterns. Codas have led researchers to propose that sperm whales belong to distinct cultural clans, but it is presently unclear if they also convey individual information. Coda clicks comprise a series of pulses and the delay between pulses is a function of organ size, and therefore body size, and so is one potential source of individual information. Another potential individual-specific parameter could be the inter-click intervals within codas. To test whether these parameters provide reliable individual cues, stereo-hydrophone acoustic tags (Dtags) were attached to five sperm whales of the Azores, recording a total of 802 codas. A discriminant function analysis was used to distinguish 288 5 Regular codas from four of the sperm whales and 183 3 Regular codas from two sperm whales. The results suggest that codas have consistent individual features in their inter-click intervals and inter-pulse intervals which may contribute to individual identification. Additionally, two whales produced different coda types in distinct foraging dive phases. Codas may therefore be used by sperm whales to convey information of identity as well as activity within a social group to a larger extent than previously assumed.

Deep Machine Learning Techniques for the Detection and Classification of Sperm Whale Bioacoustics

“…These results suggest the validity of employing ML-based techniques to advance the study of sperm whale bioacoustics and provide a practical technique to deal with the scarcity of labeled data by using self-supervised pretraining on a proxy task. In addition, the results of the clan class and whale ID analyses indicate clan-level and individual-level characteristics of sperm whale vocalizations, in accordance with the findings of 43,44 . Thus, not only do our results provide novel computational methods and techniques; they also offer important biological insight into sperm whale vocal behavior.…”

“…We demonstrate that LSTM and GRU, RNN architectures used for speech recognition and text translation, are able to classify codas into recognizable types and to accurately predict the clan membership and individual identity of the signaler. This is a significant improvement over previous methods used to classify codas as it minimizes the role of the observer in determining any parameters a priori, which was required for coda type statistical clustering techniques involved in prior studies 43,44,59 . Nonetheless, the high coda type classification accuracies we obtain using novel ML-based methods support the previous categorization of sperm whale codas into existing, predefined types.…”

“…Clans appear to demonstrate differences in horizontal movement, social behavior, dive synchronies, diet, and foraging tactics, which may affect fitness of constituent units 37–42 . Sperm whale codas appear not only to encode clan identity, but they also may contain unit- and individual-level acoustic specificity 43–45 , which suggests that codas could potentially serve to identify individuals, social units, and the dialect as a whole. Differential coda production might function to delineate socially segregated, sympatric clans 44 .…”

Fear of Killer Whales Drives Extreme Synchrony in Deep Diving Beaked Whales

“…The consistently high diving and vocal coordination demonstrated by both tagged whale pairs and individually tagged whales within groups, covering two species and different geographical areas, strongly suggest that collective behaviour is critical for social beaked whale groups: although the obligate deep vocal foraging intervals put beaked whales at risk of detection and stalking by killer whales performing passive acoustic tracking, beaked whales are safe to vocalize while in their deep refuge and their collective diving behaviour frees them from the need to vocalize during ascents to re-join non-diving members at the surface. This is in contrast to pilot whales or sperm whales that often vocalize during ascents to mediate group reunion acoustically [10][11][12][13] . That beaked whales of different genera (Mesoplodon, Ziphius) show the same coordinated behaviour suggests that the coordination of diving and vocal activity in social groups may have evolved millions of years ago or has had sufficient evolutionary value as to drive convergence towards a strikingly similar strategy.…”

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

“…Apart from a geographic variation in repertoire, group-specific dialects have been found in interacting groups with overlapping geographic range [367,375]. It has been suggested that clicks serve communication, individual identification and echolocation purposes and may be used to debilitate prey [144,326,336,342,354,357,370,[376][377][378][379][380][381].…”