‘Alphabet’ of sounds reveals complexity of sperm whale communication, scientists say

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Scientists have accomplished an incredible feat. They identified a previously unknown complexity in whale communication by analyzing thousands of recorded sperm whale click sequences with artificial intelligence.

Variations in the tempo, rhythm and duration of whale click sequences, called codas, weave a rich acoustic tapestry. These variables suggest that whales can combine click patterns in a variety of ways, mixing and matching phrases to convey a wide range of information to each other.

What sperm whales say with their clicks remains a mystery to human ears. Still, discovering the scope of whale vocal exchanges is an important step toward linking whale songs to specific social messages or behaviors, scientists reported May 7 in the journal Nature Communications.

“This work builds on much previous work focused on understanding sperm whale calls. However, this is the first work that has begun to analyze sperm whale songs in their broader communicative context and in the context of exchanges between whales, which made some of the findings possible,” said study co-author Dr. Daniela Rus, director of MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL), via email.

“Understanding which aspects of their codas they can control and vary helps us understand how they can encode information in their calls,” Rus said.

The researchers dubbed their catalog of sound combinations the “phonetic alphabet” for sperm whales, comparing variations in whale click sequences with the production of different phonetic sounds in human speech.

But while the team’s findings are interesting, that term offers a misleading perspective on whale vocal interactions, Dr. Luke Rendell, a researcher at the University of St. Louis, said in an email.

“The ‘phonetic alphabet’ presentation is nothing like that,” said Rendell, who was not involved in the research.

“The way tempo variation is used is completely different from how, say, we use elements of an alphabet to construct linguistic expression,” he said. “There’s no evidence for that, and it’s not a very useful interpretation because it forces everything into a narrow and somewhat exaggerated perspective of ‘is it like human language or not’ when there is a much wider range of interpretations available.”

Sperm whales produce their clicks by forcing air through an organ in their heads called spermaceti, and these sounds can be as loud as 230 decibels – louder than a rocket launch and capable of rupturing human eardrums – another team of scientists reported. previously in the journal Scientific Reports.

For the new study, researchers used machine learning to detect patterns in audio data collected by The Dominica Sperm Whale Project, a repository for observations of sperm whales that inhabit the Caribbean Sea. The recordings represented the voices of approximately 60 sperm whales – a subset of a group of around 400 whales known as the Eastern Caribbean clan – and the vocalizations were recorded between 2005 and 2018.

Previous research has identified 150 types of codas in sperm whales around the world, but Caribbean whales only used 21 of these codas.

Scientists examined the timing and frequency of 8,719 coda sequences – in solitary whale utterances, in choruses, and in call-and-response exchanges between whales. When visualized with artificial intelligence, never-before-seen coda patterns emerged.

The study authors defined four characteristics in codas: rhythm, tempo, rubato and ornamentation. Rhythm describes the sequence of intervals between clicks. Time is the duration of the entire coda. Rubato refers to variations in duration between adjacent codas of the same rhythm and tempo. And ornamentation is an “extra click” added at the end of a coda in a group of shorter codas, Rus explained.

These so-called ornamental clicks “occur more at the beginning and end of turns” during vocal exchanges between whales, “behaving like speech markers,” Rus said.

The discovery that whales could synchronize variations in coda timing was “a really interesting observation,” Rendell said.

“I’m less convinced by the ‘ornamentation,’” he added. “This occurs very rarely, and I think we need more evidence that these aren’t just production glitches” or filler sounds, “like when we say ‘um’ or ‘err’.”

In total, the program detected 18 types of rhythm, five types of tempo, three types of rubato and two types of ornamentation. These coda features could all be mixed and matched to form a “huge repertoire” of phrases, the study authors reported. Furthermore, the meaning could be further adjusted depending on the placement of a coda – following or overlapping other codas – within an exchange or chorus involving two or more whales.

“In fact, many of us have been waiting for advanced technology that would allow us to do something like this for decades!” said Dr. Brenda McCowan, a professor at the University of California Davis School of Veterinary Medicine, in an email.

McCowan, who was not involved in the research, was part of another team that, in 2021, conducted an interactive “conversation” with a humpback whale in waters near Alaska. For about 20 minutes, a curious whale repeatedly responded to a recording of a humpback song broadcast from the scientists’ boat.

“This particular breeding (with the humpback in 2021) was an opportunistic experiment with a curious whale engaging us both behaviorally and vocally, and completely of its own volition,” McCowan said.

This interactive experimentation with whales, along with observations of whale behavior, could be an important part of unraveling the syntax of sperm whale click sequences, the authors wrote in the study.

Their machine learning method could also be useful for studying other types of animal vocalizations, McCowan added.

“It is likely that the tempo, rhythm, rubato and ornamentation are found in other whale species,” McCowan said. “We already know that this applies to humpback songs. But there is also evidence of this type of pattern in other aquatic, terrestrial and arboreal species to which this approach could be applied.”

But while this technique is useful for identifying certain aspects of communication, it is not a Rosetta Stone, Rendell cautioned.

“Machine learning is great for finding patterns in large data sets,” he said, “but it doesn’t create meaning.”

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works.