Off the coast of Mallorca, and later near Crete, sperm whales gather and communicate with each other. Their conversations sound somewhat different depending on which side of the sea you listen from.
A fresh analysis of recordings collected over two decades has revealed that these whales use two distinct dialects. The study’s findings were published in the journal Proceedings of the Royal Society B.
One whale group belongs to the western Mediterranean, while the other is from the eastern part, and the divide between them tells a story of how culture shifts within an isolated population.
The population is small and cut off from whales in other oceans. The International Union for Conservation of Nature (IUCN) lists this species as endangered, with only a few thousand individuals remaining.
Sperm whales are the largest of the toothed whales. They produce short sequences of clicks, known as codas, and these acoustic signals act as a form of social marker.
Whales that share the same coda patterns belong to a single vocal clan. These codas indicate their group affiliation and who they associate with, much like a shared language unites a community.
For many years, the Mediterranean population was viewed as one unified clan. Nearly every recorded coda followed a single rhythm, called 3+1: three evenly spaced clicks, a pause, and then a final click. This uniformity made the group unusually straightforward compared to whales elsewhere.
The new study challenges this orderly picture. Researchers analyzed 5,291 codas recorded between 2003 and 2021 from whales near the Balearic Islands in the west and the Hellenic Trench off Greece in the east.
When the codas were sorted into groups, two clear dialects emerged. Western whales used a slow version of 3+1, while eastern whales employed a faster, modified form.
The recordings resulted from years of painstaking work at sea. Teams tracked whales by their clicks, recorded the codas, and measured the gaps between them. In total, the analysis covered 112 days spent on the water and over a hundred individual whale sightings. This broad scope made the pattern unmistakable.
The eastern dialect stands out with two distinctive concluding phrases that are extremely rare in the west. One variation is a fast four-click rhythm, and the other is an eight-click coda where the intervals between clicks steadily increase.
In the western dialect, by contrast, slower and longer codas dominate. When compared, both versions sound like the same phrase delivered at different speeds. One detail stood out in the recordings: eastern whales sometimes abandon their fast dialect and instead use the slower western form.
The opposite almost never happens. Western whales were rarely caught using eastern dialects, and this uneven pattern points to a clear trend in how the dialects formed.
“These results paint a picture of sperm whale history in the Mediterranean, consistent with a gradual westward-to-eastward colonization, culminating in the development of a distinct dialect among animals living in the east, starting from the Hellenic Trench,” said lead author Taylor Hersh. “What’s interesting is that the new dialect is clearly a modified version of the presumably ancient slow 3+1, and that eastern population groups also distinctly recall this dialect, since they retain these ‘throwback’ timings.”
The asymmetry suggests that the slow western dialect is older. Eastern whales carried it with them and then built something new on top of it.
This fast eastern dialect appears to be a recent invention layered onto an inherited foundation. The whales added to their vocal tradition without losing the original.
The findings match what is known about how these whales entered the Mediterranean. Sperm whales are thought to have entered the sea around 20,000 years ago through the Strait of Gibraltar.
From there, they spread eastward, and the dialects seem to follow that same route. Even the few whales whose movements between basins were tracked always moved only from west to east.
“The Mediterranean has been a cradle for important aspects of human cultural evolution, starting with ancient Greece,” said Luke Rendell, who coordinated the work at the University of St Andrews. “Throughout that period, sperm whale culture has also been evolving—now we have a much better understanding of how slow this process is. It also helps us grasp the origins of dialect diversity in sperm whales worldwide. But many questions remain unanswered, such as why this new dialect arose at all and specifically in this location.”
Despite the clear division, the two groups are not yet fully separate clans. Some eastern social groups can still switch between dialects from one day to the next.
Such flexibility is rare. It suggests that the Mediterranean whales are at an intermediate stage in a slow process of splitting into distinct clans.
“This discovery reminds us that the cultural history of the Mediterranean does not belong exclusively to humans,” said Tshema Broughtons from the Tursiops Association. “While the civilizations of Mare Nostrum developed their own languages, customs, and identities, sperm whales were also passing down their vocal traditions from generation to generation.”
The Mediterranean is a place of shared cultural diversity, where human and animal cultures have coexisted and evolved together for millennia.
These whales face serious threats from ships and entanglement in fishing gear. With so few individuals left, every bit of information about population structure matters.
Studying their dialects helps map this structure and shows how culture itself can guide conservation efforts. Differences in vocal data offer a window into a population that we are still trying to understand.
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