Complex Communication Patterns in Sperm Whales

Sperm whales are highly social marine mammals that live in culturally transmitted matrilineal societies. Within these societies, individuals exhibit sophisticated social behaviours such as collective decision-making and cooperative foraging. To coordinate these interactions, sperm whales employ an acoustic communication system composed of patterned click sequences known as codas.

Sperm whale（Image source：Gabriel Barathieu ， CC BY-SA 2.0 ）

These codas are structured sequences consisting of three to forty consecutive clicks arranged in fixed temporal patterns. Sperm whales produce such sequences during social interactions and while exchanging signals between long, deep foraging dives.

Different cultural clans of sperm whales possess distinct repertoires of codas, and these clans also differ in behavioural traditions. Previous studies have identified roughly 150 coda types worldwide, including 21 types recorded in the Caribbean. However, the apparent simplicity of this limited set of signals seems inconsistent with the complex social organisation observed in sperm whales. This discrepancy has led researchers to suspect that additional, previously unrecognised structure might exist within the whales’ communication system.

Two sperm whales from the Dominica dataset exchanging click sequences for two minutes（Image source：Sharma, P et al(2024). ， CC BY 4.0 ）

To investigate this possibility, a research team analysed a large acoustic dataset collected from the Eastern Caribbean EC-1 clan. This clan contains more than 400 individuals. The analysed dataset included 8,719 recorded codas from at least 60 whales collected between 2005 and 2018. These recordings together encompassed the previously described 21 Caribbean coda types.

The analysis revealed that sperm whale codas are not rigid, fixed sound units. Instead, whales introduce subtle variations when communicating. During exchanges, individuals slightly adjust the rhythm and timing of their clicks in response to preceding signals. They may also add additional clicks to an existing sequence. Furthermore, whales are capable of combining these variations across different coda patterns, generating a much larger number of distinguishable acoustic signals than previously recognised. Importantly, whales respond differently to these variations, indicating that they perceive the distinctions and that these differences are meaningful components of communication rather than random noise.

Researchers identified four principal structural features that generate variation within codas.

Tempo: refers to the overall duration of a coda, that is, the speed from the first click to the last. Different codas tend to cluster around several discrete duration categories.

Rhythm: describes the distribution pattern of intervals between clicks within a coda. Even when total duration changes, the relative spacing between clicks may remain similar.

Rubato: denotes gradual changes in timing across successive codas produced by the same whale. In such cases, a whale may slowly increase or decrease the duration of its codas during an exchange, and other whales sometimes imitate these shifts.

Ornamentation: refers to additional clicks appended to the end of a coda that otherwise resembles neighbouring sequences. These extra clicks are not randomly placed; instead, they appear at specific positions during extended exchanges.

Four types of variation in sperm whale communication codas: A tempo, B rhythm, C rubato, D ornamentation（Image source：Sharma, P et al(2024). ， CC BY 4.0 ）

Together, these four features form a combinatorial system. Instead of relying solely on a small inventory of fixed signals, sperm whales can produce a large number of distinct codas by combining different rhythms, tempos, rubato patterns, and ornamentation elements. This structure resembles the way human languages generate numerous utterances from combinations of a limited set of phonetic features.

Phonetic alphabet of sperm whale communication codas（Image source：Sharma, P et al(2024).， CC BY 4.0 ）

Using the analysed dataset, researchers estimated that codas include approximately five tempo categories, eighteen rhythm patterns, three types of rubato variation, and several optional ornamentations. When these elements combine, the potential information capacity of the communication system increases substantially, possibly doubling earlier estimates based only on the previously recognised 21 coda types.

Despite revealing this structural complexity, the study did not attempt to determine the meanings conveyed by specific codas. The research instead focused on identifying the underlying architecture of the communication system. Understanding the semantics of whale communication will require further investigation, particularly interactive playback experiments with wild whales that test how individuals respond to specific signal patterns.

These findings indicate that sperm whale vocal communication possesses a structured combinatorial system capable of encoding far more information than previously recognised. The results also suggest that complex sound-based communication systems, resembling some structural aspects of human language, may arise in species with very different evolutionary histories and vocal mechanisms.

Author: Bai Leng

Reference:

Sharma, P., Gero, S., Payne, R., Gruber, D. F., Rus, D., Torralba, A., & Andreas, J. (2024). Contextual and combinatorial structure in sperm whale vocalisations. Nature Communications.