The staccato clicks produced by sperm whales might strike human ears as mere meaningless background noise, but recent analysis suggests they are actually part of a communication system whose complexity nears our own. The findings of this study were recently published in the journal Proceedings of the Royal Society B: Biological Sciences.
According to researchers from Project CETI, an American non-profit dedicated to sperm whale study, the clicks, known as “codas,” exhibit greater complexity than what was indicated in a 2024 paper. That earlier work had established that these sounds bore acoustic resemblance to human vowels.
The new paper, which investigates five specific properties of these coda sounds, demonstrates that they are employed in sequences adhering to structured rules analogous to those observed in human speech.
“All five properties feature close parallels in the phonetics and phonology of human languages, suggesting independent evolution,” states the research team, led by linguist Gaspar Begush of Project CETI. “Sperm whale coda vocalizations are thus exceptionally complex, representing one of the closest parallels to human phonology yet observed across any animal communication system analyzed.”
Sperm whales (Physeter macrocephalus) are large marine mammals living in tightly knit matrilineal clans, characterized by strong bonds and cooperative relationships that afford them greater competitive advantage in harsh ocean environments. Such sophisticated social structures typically necessitate equally sophisticated communicative abilities.
It has long been hypothesized that cetacean communication is far more elaborate than readily apparent, particularly in sperm whales. Their gatherings are frequently accompanied by bursts of clicks that can travel many kilometers across the ocean.
In 2024, Project CETI researchers analyzed 8,719 coda vocalizations, recorded from a minimum of 60 individual whales between 2005 and 2018, and found them to be “more expressive and structured than previously understood,” with characteristics that could combine in ways comparable to elements of human speech.
That prior work proposed that whale communication involved flexible, combinable elements but did not explore how these elements were internally structured.
In the current article, Begush and his colleagues analyzed 3,948 coda sequences from 15 individuals, recorded between 2014 and 2018 as part of the Dominican Sperm Whale Project in the Eastern Caribbean Sea, aiming to uncover at least some of these underlying structures.
The researchers discovered that sperm whale coda sounds diverge into distinct categories that behave similarly to vowels in human speech, exhibiting consistent differences in duration, structure, and their interaction with adjacent sounds.
They identified two distinct types of coda sounds possessing differing formant structures—that is, the structure of the sound’s resonant frequencies. Coda sounds with a single formant were designated as “a-codas,” while those with two formants were termed “i-codas.”
These a-codas and i-codas not only acoustically resemble human vowels but also exhibit analogous behavior in several other respects. For instance, a-codas are longer than i-codas, and i-codas also feature both shorter and longer variants.
Individual whales also demonstrate unique rhythms in their use of these coda sounds, and neighboring sounds can influence one another, much like diphthongs in human speech, such as when the sounds ‘a’ and ‘oo’ combine to form the sound ‘oh’.
“We have demonstrated that the sperm whale communication system possesses previously uncharacterized features that render it similar to human phonology,” the researchers conclude.
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