Something as simple as the word you use for a bread roll (cob, bun, bap, batch or barm cake, for example) can tell people a lot about where you’re from and your identity. But dialects like these aren’t unique to humans.
Researchers have discovered that sperm whale clans on different sides of the Mediterranean Sea have different dialects. The study is published in the scientific journal Proceedings of the Royal Society B.
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When marine scientists analysed 5,291 codas – the rapid morse-code-like sequence of clicks that sperm whales use to communicate – from the eastern and western Mediterranean Sea, they noticed distinct differences.
“As soon as we started listening to sperm whale recordings from both regions, the differences between them were actually very stark,” says the study’s author Taylor Hersh, a bioacoustician at Bristol University and Oregan State University’s Marine Mammal Institute.
“The whales in the western Mediterranean make a single coda type very often, whereas the whales in the eastern Mediterranean have a much more varied coda repertoire,” says Hersh.
An isolated population
Sperm whales are found in every ocean on the planet but this population is unique, she says: “From genetics research by Biagio Violi and colleagues, we believe sperm whales first entered the Mediterranean Sea through the Strait of Gibraltar about 20,000 years ago.”
Once they arrived, they stayed, even though the Strait of Gibraltar should be deep enough for them to leave again, Hersh says.
This could be because sperm whale behaviours are passed down over generations.
“If their social unit never leaves the Mediterranean Sea, they're unlikely to leave the Mediterranean Sea either,” says Hersh.
“We are probably seeing whales conforming to their cultural practice and staying in a region that has been their ancestors' home for a very long time.”
This small, genetically isolated population is the only sperm whale subpopulation listed as endangered by the International Union for Conservation of Nature (IUCN).
They are also outliers because both sexes stay home together and males don’t leave for long migrations. In the Med, “male and female sperm whales share the same waters for their entire lives,” says Hersh. “Adult male and female sperm whales outside of the Mediterranean live largely separate lives.”
Despite their genetic similarities and close-knit groups, eastern and western clans sounded different. This fact in itself wasn’t striking. “I was surprised by how different they were, and how apparent those differences were to the “naked ear,” she says.
Their most common coda has the same rhythm – “three equally spaced clicks and an extended pause before the fourth and final click,” says Hersh. This is called 3+1 – but the tempo is different. “Eastern whales make it much, much more quickly,” says Hersh.
When sperm whales first arrived into the Mediterranean, they are thought to have first settled in the western basin before some individuals moved east. Today, whales don’t tend to switch between the two. “When it has been documented, it is always western whales moving to the east,” she says.
In the west, sperm whales are mainly communicating using this simple, “ancestral” dialect. Meanwhile, eastern sperm whales’ more diverse dialect may have changed over time.
This makes the experts think these dialects mirror this early sperm whale movement. “The first whales made home in the western basin, but some animals eventually moved east, taking the “ancestral” western dialect with them but then subsequently changing and diversifying it,” she says.
In rare instances, some eastern whales switched between the two, producing the slow 3+1 coda typical of western whales.
“We think eastern whales still remember the ancestral western dialect and occasionally produce it,” Hersh adds. “The western whales have likely never or rarely encountered the eastern dialect, and so they stick to the dialect they know.”
This fascinating discovery reminds us how much there is yet to learn about sperm whale culture.
“This finding reminds us that the cultural history of the Mediterranean does not belong exclusively to humans,” says Txema Brotons, a researcher from Asociación Tursiops, in a press release.
“While the civilisations of the Mare Nostrum were developing their own languages, customs, and identities, sperm whales were also passing down their vocal traditions from one generation to the next.”
