Sperm whales have developed the ability to adopt new calls used by other populations while still retaining their original “dialect”, scientists have found.
An international team studying endangered sperm whales in the Mediterranean Sea have captured how those dialects evolve using 20 years of recordings.
The researchers, led by the University of St Andrews in Scotland, found that whales living around the Hellenic Trench in Greece had developed a new form of the dialect used by animals nearer the Balearic Islands.
It is thought sperm whales first entered the Mediterranean about 20,000 years ago, spreading from Gibraltar and establishing themselves throughout the region. They were discovered living near Greece three decades ago.
They are genetically isolated from other oceans and have a population of a few thousand. They are considered endangered due to their limited numbers and serious threats from fishery entanglement and ship strikes.
Sperm whales communicate using short, stereotyped patterns of clicks to identify themselves as belonging to larger cultural groups called vocal clans.
Previously it was thought all the whales in the Mediterranean belonged to the same clan, identified by a single predominant vocal type consisting of three clicks and then a pause before the fourth and final one. The pattern is called the “3+1" type.
The new results, published in Proceedings of Roal Society B showed that whales around the Hellenic Trench, a deep water feature centred off Crete, produced a distinct, faster version compared to animals in the western basic between Gibraltar and Italy.
The scientists found that these whales would switch between the two dialects.
“The Mediterranean has been the cradle of significant aspects of human cultural evolution from ancient Greece onwards,” said Dr Luke Rendell, reader at the University of St Andrews Sea Mammal Research Unit who co-ordinated the study.
“Over that entire period, sperm whale culture has also been evolving – we now have a much better idea of just how slow that process is. It also helps us understand the origins of dialect diversity in sperm whales globally. But there are still many unanswered questions, like why that new dialect evolved at all and in that particular location.”
Lead author Dr Taylor Hersh, from the University of Bristol, highlighted how the whales switch between dialects.
“These findings paint a picture of the history of sperm whales living in the Mediterranean, consistent with a progressive occupation from west to east, ending with the development of a distinctive dialect in the animals living in the east, starting in the Hellenic Trench,” Dr Hersh said. “What’s interesting is that the new dialect is clearly modified version of the presumably ancestral slow 3+1 and that groups in the east also clearly remember that dialect as they have these ‘throwback’ days.”
The researchers said that studying these dialects provides important new information about the population structure and social dynamics of the endangered whales.
Dr Txema Brotons, of Asociacion Tursiops, the Spanish team involved in the study, said the findings were a reminder that the cultural history of the Mediterranean does not belong exclusively to humans.
“The Mediterranean is therefore a space of shared cultural diversity, where the evolution of human culture and animal culture has coexisted for thousands of years,” he said.
Last week, a separate study found an Arabian Sea humpback whale, which usually hugs the coastline of Oman, had a journey to Goa in search of food or a mate.
This is the first direct evidence that the species crossed the Arabian Sea and is considered by scientists to be a behavioural anomaly because its members are so uniquely adapted to their habitat.
