Researchers discovered a previously unknown ‘alphabet’ in sperm whale calls

Scientists have made great strides in understanding whale communication by identifying previously unknown complexities in sperm whale click sequences using artificial intelligence (AI). By analyzing thousands of recorded sequences, researchers have uncovered variations in tempo, rhythm, and length of the whales' clicks, known as codas. These variations suggest that sperm whales can combine click patterns in multiple ways to convey a broad range of information.

The exact meanings of these click sequences remain a mystery, but this discovery is a crucial step toward linking whale calls to specific messages or social behaviors. The study, published in the journal Nature Communications, represents a major advancement in the field of marine mammal communication.

"This work builds on a lot of prior work focused on understanding the calls of sperm whales. However, this is the first work that has started to look at sperm whale calls in their wider communicative context and in the context of exchanges between whales, which has made some of the findings possible," said Dr. Daniela Rus, director of the Computer Science and Artificial Intelligence Laboratory (CSAIL) at MIT and coauthor of the study.

Rus explained that understanding the aspects of their codas that whales can control and vary helps researchers comprehend how these animals encode information in their calls.

The researchers referred to their catalog of sound combinations as a "phonetic alphabet" for sperm whales, comparing the variations in the whales' click sequences to the production of different phonetic sounds in human speech.

However, Dr. Luke Rendell, a marine mammal communication expert at the University of St. Andrews, expressed concerns about this terminology, suggesting it might offer a misleading perspective on whale vocal interactions. He emphasized that the way tempo variation is used by whales differs significantly from how humans use elements of an alphabet to construct linguistic expressions.

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Sperm whales produce their clicks by forcing air through an organ in their heads called the spermaceti. These sounds can reach up to 230 decibels—louder than a rocket launch and capable of rupturing human eardrums.

For this study, researchers used machine learning to detect patterns in audio data collected by The Dominica Sperm Whale Project, which documents observations of sperm whales in the Caribbean Sea. The recordings, representing the voices of approximately 60 sperm whales from the Eastern Caribbean clan, were made between 2005 and 2018.

Previous research had identified 150 types of codas in sperm whales globally, but Caribbean whales used only 21 of these codas. The scientists examined 8,719 coda sequences in various contexts, including solitary whale utterances, choruses, and call-and-response exchanges between whales. Using AI, they visualized these codas and uncovered previously unseen patterns.

The study identified four features in codas: rhythm, tempo, rubato, and ornamentation. Rhythm refers to the sequence of intervals between clicks, tempo is the duration of the entire coda, rubato involves variations in duration across adjacent codas of the same rhythm and tempo, and ornamentation is an extra click added at the end of a coda. These features combine to create a vast repertoire of phrases, with meaning potentially influenced by the placement of a coda within an exchange or chorus.

Dr. Brenda McCowan, a professor at the University of California Davis School of Veterinary Medicine, praised the use of advanced technology in this study. McCowan, who was not involved in the research, highlighted the potential for such technology to advance understanding of animal communication. She noted that features like tempo, rhythm, rubato, and ornamentation are likely present in other whale species and possibly other animals, making this approach broadly applicable.

However, Dr. Rendell cautioned that while machine learning is excellent for finding patterns in large datasets, it doesn't create meaning. He stressed the need for further research to fully understand the significance of these patterns in whale communication.

Interactive experimentation with whales, along with observations of whale behavior, could be key to unraveling the syntax of sperm whale click sequences. In 2021, McCowan was part of a team that conducted an interactive "conversation" with a humpback whale in Alaska, where the whale responded to a recording of a humpback song transmitted from a boat. Such experiments, combined with the findings of the recent study, hold promise for decoding the complex vocalizations of sperm whales and potentially other marine mammals.

By leveraging machine learning and extensive audio data, researchers have taken a crucial step towards understanding the rich and complex language of these majestic creatures. As technology advances, so too will our ability to decode the secrets of whale communication, offering deeper insights into the social behaviors and interactions of these remarkable animals.

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