Different sperm whale ‘dialects’ detected on separate sides of the Mediterranean

From “Howdy” to “G’day”, English – like other languages – is rich in dialects. Now researchers have found sperm whales on different sides of the Mediterranean show similar variations in their vocalisations.

Sperm whales communicate vocally using sequences of short clicks called codas. However, the rhythmic pattern of these clicks, known as the dialect, can differ between different matriarchal groups.

Crucially, one group of sperm whales will only associate with another if they share the same dialect and hence belong to the same “vocal clan”.

“The dialect is used to form social structures, within which these animals will cooperate,” said Dr Luke Rendell, of the University of St Andrews and a co-author of the new study, noting similarities in how humans might be more comfortable striking up a conversation with someone who sounds similar to themselves.

Now Rendell and colleagues say they have discovered two different dialects among Mediterraean sperm whales – a small, endangered population of a few thousand individuals that are thought to have first entered these waters about 20,000 years ago.

What’s more, they say the finding offers new insights into how sperm whale dialects arise.

Writing in the journal Proceedings of the Royal Society B, the team note genetic studies have previously suggested Mediterranean sperm whales have become isolated from other sperm whales. There are also signs that mating between those in the western and eastern Mediterranean basins is restricted, although individuals have been spotted moving between the two.

In the new study the researchers analysed hydrophone recordings of groups of Mediterranean sperm whales made over 112 days between 2003 and 2021. These were recorded around the Hellenic Trench near Greece in the eastern Mediterranean and around the Balearic Islands, off the coast of Spain in the western basin.

While the team found some codas were largely confined to either eastern or western groups, they found in both areas most sperm whale codas involved four clicks.

However, while whales in the western Mediterranean basin favoured a 3+1 coda involving three regularly spaced clicks followed by a longer pause, then another click, those in the eastern basin tended to use a faster version. But there was crossover, with sperm whales in the eastern basin occasionally producing the western dialect.

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Rendell said the findings suggested sperm whales first established themselves in the western basin of the Mediterranean before spreading eastwards and developing a faster dialect.

“The whales in the east remember the old ways, but they’re moving on and they’ve got a slightly different version of what is clearly the same [general type of coda], but they’ve evolved it a little bit; they’ve changed it,” he said.

Rendell added that the results not only showed the process of dialect formation was slow, but that it required some level of isolation between populations – something the authors note is also important in the cultural evolution of human languages and birdsong dialects.

“This is the first example we’ve got where we can look at a snapshot and think: ‘Oh, this seems to be telling us about how new dialects come about’,” Rendell said. “We just knew there were these different dialects, but we’ve never seen the origin or had any clues into the origin of them. And we see here how a group of sperm whales that’s split off from a main population has now started to change its dialect as well.”