Talking To A Non-human Intelligence: Sperm Whale Vocalisations
Sperm whales (Physeter macrocephalus) are highly social mammals that communicate using sequences of clicks called codas. While a subset of codas have been shown to encode information about caller identity, almost everything else about the sperm whale communication system, including its structure and information-carrying capacity, remains unknown. We show that codas exhibit contextual and combinatorial structure.
First, we report previously undescribed features of codas that are sensitive to the conversational context in which they occur, and systematically controlled and imitated across whales.
We call these rubato and ornamentation. Second, we show that codas form a combinatorial coding system in which rubato and ornamentation combine with two context-independent features we call rhythm and tempo to produce a large inventory of distinguishable codas. Sperm whale vocalisations are more expressive and structured than previously believed, and built from a repertoire comprising nearly an order of magnitude more distinguishable codas.
These results show context-sensitive and combinatorial vocalisation can appear in organisms with divergent evolutionary lineage and vocal apparatus.
Sperm whales communicate by producing sequences of clicks. A Shows a two-minute exchange between two whales (with clicks visualized in blue and orange respectively) from the Dominica Sperm Whale Dataset. B Projects these clicks over a time–time plot, in which the horizontal axis plots the time in the exchange at which a click occurs, and the vertical axis represents the time of the click from the first click in the coda. The vertical axis serves as a microscope over the horizontal axis, revealing the internal structure of each coda. C Shows a time–time visualisation for the entire two-minute exchange (with lines connecting matching clicks between adjacent codas), revealing complex, context-dependent variation in coda structure. — Nature
Contextual and combinatorial structure in sperm whale vocalisations, Nature (open access)
Astrobiology
