Researchers from Project CETI and collaborating institutions have developed a method to investigate sperm whale communication by determining their vocal style, finding that groups living in close proximity can develop similar styles to each other. Published in eLife, the study is deemed important by editors for contributing to a richer understanding of communication between whales and providing evidence for social learning between neighbouring sperm whale clans. The methodology developed could also be applied to compare communication systems in other species to gain a deeper insight into vocal and cultural transmission within non-human societies.
Sperm whales live in multilevel societies that allow for complex social behaviors and the transmission of knowledge and cultural behaviors across generations. They communicate through rhythmic patterns of clicks called codas, with the vocal repertoire of a group defining its clan membership. While individual variations in vocal repertoires exist, whales within the same social unit share a common vocal repertoire lasting many years, referred to as being part of the same clan. Different clans are distinguished by identity codas, which make up a minority of total codas vocalized by each whale, with clear social segregation between members of different clans even when they live close together.
A novel method developed by the researchers breaks down each coda into a sequence of inter-click intervals (ICIs), creating a model using variable length Markov chains to estimate the probability of observing a specific ICI based on the previous one. This data is then used to construct a “subcoda tree” containing important rhythmic variations and transitions within ICIs, revealing information about an individual whale or clan’s vocal style. The validity of the method was confirmed through the analysis of two datasets of sperm whale vocalizations from the Pacific and Atlantic Oceans, accurately sorting recorded whales into their respective clans based on their vocal style.
Spatial proximity between sperm whale clans and social units impacts their vocal style, with closer proximity resulting in greater similarity in non-identity coda vocal styles, suggesting social learning between clans. While identity codas are consistently maintained for clan recognition, social learning may lead to a more similar vocal style with other whales within acoustic range. The authors call for further research to confirm evidence of social learning in sperm whales through larger dataset analyses and longitudinal studies over time to rule out genetic or environmental factors. This research strengthens the use of identity codas as symbolic markers and supports the idea of cultural transmission and social learning of vocalizations among whales from different clans.
In conclusion, the findings suggest that vocal learning in sperm whales may not be limited to vertical transmission within families but also involve horizontal social learning between clan members. The study contributes to a better understanding of sperm whale communication, highlighting the importance of social learning in shaping vocal styles within populations. Additional research is needed to further explore the role of social learning in whale communication and better understand the mechanisms behind the development and maintenance of vocal styles within various clans.
