Sperm whales in the Mediterranean Sea have been found to possess distinct 'dialects', with populations on either side of the basin employing different vocal patterns. The discovery, revealed by a new study, offers valuable insights into how complex communication systems evolve and shape the social structures of these intelligent marine mammals.
The research, led by Dr Luke Rendell of the University of St Andrews, centred on the sequences of short clicks, known as codas, that sperm whales use to interact. These rhythmic click patterns – or dialects – dictate which matriarchal groups will associate with one another, forming 'vocal clans', much like shared linguistic traits can foster comfort and cooperation within human communities.
Researchers analysed hydrophone recordings collected over 112 days between 2003 and 2021. These recordings captured sperm whale vocalisations near the Hellenic Trench in the eastern Mediterranean, off Greece, and around the Balearic Islands, off Spain, in the western basin. With only a few thousand individuals remaining, the Mediterranean sperm whale population is small and endangered – believed to have entered these waters approximately 20,000 years ago.
While most codas in both regions involved four clicks, the rhythmic arrangement differed significantly. Western whales predominantly used a '3+1' coda, featuring three regularly spaced clicks followed by a longer pause and then a final click, whereas eastern counterparts tended to employ a faster version of this pattern – although some crossover was observed, with eastern whales occasionally producing the western dialect.
Dr Rendell suggests these findings indicate that sperm whales initially established themselves in the western Mediterranean before migrating eastwards, where the faster dialect subsequently developed. He explained that the eastern whales "remember the old ways, but they’re moving on and they’ve got a slightly different version." This process of dialect evolution, the study noted, highlights its slow nature and underscores the importance of population isolation – a factor also significant in human languages and birdsong dialects.