Sperm whales considered ‘oddballs’ may be developing two distinct communication patterns, according to sonic evidence

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Sperm whales within the Mediterranean appear to have diverged into two distinct groups, each possessing its own unique vocal patterns.

A geographically contained population of sperm whales in the Mediterranean Sea is separating into two unique communities, each with its own distinct dialects, recent research indicates. This divergence has likely been in progress for millennia, originating from an initial single populace.

The discoveries, disseminated on Tuesday (June 23) in the journal Proceedings of the Royal Society B: Biological Sciences, offer a rare perspective into the evolution of varied dialects among non-human species.

Sperm whales (Physeter macrocephalus) subsist in small familial units of females and juveniles, and they connect with similar aggregations within their vicinity. They employ social vocalizations referred to as codas — brief sequences of clicks — for communication. The specific codas they utilize signify their affiliation with a particular cultural collective.

Taylor Hersh, an investigator at the School of Biological Sciences, University of Bristol, U.K., and the primary author of the study, along with her associates, examined coda recordings gathered over nearly two decades in the Mediterranean. This region hosts a singular population of a few thousand sperm whales. Their objective was to ascertain if they all communicated using the same dialect.

Sperm whales infiltrated the Mediterranean approximately 20,000 years ago through the Strait of Gibraltar, subsequently spreading across the expanse. The whales seldom depart the sea, even males, who typically undertake migrations. Other sperm whale populations rarely enter, rendering the Mediterranean inhabitants effectively isolated and classified as an endangered subspecies.

“The sperm whales in the Mediterranean are truly fascinating,” Hersh communicated to Live Science. “I’ve always viewed them as the outliers of the sperm whale world, in that they don’t exit via the Strait of Gibraltar despite the possibility. They are unique, and for a considerable period, they were also believed to be acoustically distinct.”

The prevailing notion was that all Mediterranean sperm whales belonged to a single clan, identified by their consistent use of one specific coda 90% of the time. This coda comprises three clicks followed by a pause before the fourth and final click — a structure known as the three-plus-one type.

However, the analysis conducted by Hersh’s team, involving 5,291 codas documented between 2003 and 2021, indicated that sperm whales inhabiting the eastern Mediterranean, in the vicinity of the Hellenic Trench off Greece, exhibit a subtly different dialect compared to those in the western basin near Spain’s Balearic Islands.

The whales in the eastern region produce a unique variation of the three-plus-one coda. “It’s a highly similar pattern of clicks, but it is significantly faster,” Hersh remarked.

Distinct dialects were identified between the two whale communities, with the eastern group emitting slower codas.

In a subset of recordings, whales from the eastern Mediterranean produced the slower coda, indicating familiarity with both communication styles.

“The western sperm whales adhere strictly to their dialect, but there were four instances where eastern whales utilized the western dialect,” Hersh stated. “The reason for this remains an open question. Their dialect appears to be far more varied than initially anticipated. They do occasionally produce those slow three-plus-one codas, but they also generate numerous other types of codas.”

Hersh expresses hope that further recordings, combined with data linking specific whales to sounds and events, may help clarify why the whales switch between dialects.

“It is exciting to observe this study demonstrating that different populations behave in closely related yet distinct ways,” commented Gašper Beguš, linguistics lead at Project CETI, a non-profit organization dedicated to deciphering sperm whale communication.

The research illustrates a scenario where sperm whales progressively populated the Mediterranean from west to east, with the dialect of one group undergoing gradual modification. “The groups in the east clearly retain memory of the western dialect, as evidenced by these ‘throwback’ occurrences,” Hersh noted.

The mechanisms and motivations behind the evolution of these dialects remain enigmatic.

“Every form of speech possesses a dialect; the pertinent questions are how they originated and why,” stated Beguš, who was not involved in the current study. He suggested that the historical shifts in habitat do provide insight into which dialect emerged first. “In the Mediterranean, perhaps they are forming distinct communities, which might explain their effort to differentiate themselves,” he told Live Science, drawing a parallel to young people distinguishing themselves from prior generations by adopting new slang.

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“It’s conceivable that these two groups, with repertoires that are highly similar yet distinct, could represent an intermediate stage,” Ellen Jacobs, a marine biologist at Aarhus University in Denmark who did not participate in the research, shared with Live Science via email.

“Modifications in rhythm might serve as a highly plausible and significant method for coda signals to begin diverging,” she elaborated, likening it to how the English phrase “How do you do?” was compressed and transformed into “howdy.”

The timeframe for the development of a sperm whale dialect is uncertain, but it is likely a gradual process, according to Hersh. “It’s probably occurring on the scale of hundreds and thousands of years, considering that sperm whales can live into their 60s and 70s. And this study examines data over 19 years, which is merely a snapshot of an individual animal’s lifespan,” Hersh explained.

This suggests that the eastern whale dialect may have been developing in the Mediterranean Sea concurrently with prominent human civilizations speaking different languages in the surrounding regions, including during the rise and fall of ancient Greece and Rome.

“Perhaps if we were to observe them for another 10,000 years, we would return to find completely separate dialects among the clans,” Jacobs speculated.