Researchers in Australia listened to hundreds of hours of recordings gathered over more than a decade.
These revealed how a specific song pattern, which originated in Eastern Australia, had passed “like Chinese whispers” to whale populations up to 6,000km away in French Polynesia.
The findings are reported in the journal Current Biology.
Cultural ripples
The research team, led by Ellen Garland from the University of Queensland, say the findings show the animals transmit such “cultural trends” over huge distances.
“Within a population, all males sing the same song,” Ms Garland explained. “But that song is constantly changing. So we wanted to look at the dynamics of songs throughout an ocean basin.”
To do this, she and her colleagues studied recordings of 775 humpback whale songs, taken by scientists from the South Pacific Whale Research Consortium.
“Lots of different sounds make up each song,” Ms Garland explained.
“There are low frequency moans, groans and growls then higher cries and shrieks and all variations of ascents and descents.”
Repeating the verse
Patterns of these sounds make up phrases, and the whales repeat the phrases – like repeated verses – for up to 30 minutes.
Using sound analysis software, Ms Garland and her colleagues discovered that four new songs that had emerged in a population in Eastern Australia gradually spread westwards.
Within two years of this new song being invented, whales in French Polynesia were singing this same “version”.
“It’s a culturally-driven change across a vast scale,” said Ms Garland.
The researchers think the whales in the South Pacific may hear and learn songs during their annual migration to their feeding grounds in Antarctica.
“The East Australian population is the largest in the region with over 10,000 humpbacks,” Ms Garland explained. Since there are more of them singing, these whales may have more influence on what songs “catch on”.
Peter Tyack, a biologist from Woods Hole Oceanographic Institution in Massachusetts, US, said the results showed “a new way to look at culture in these animals”.
“These are very mobile animals; they can swim hundreds of kilometres in a day… and their song carried very well underwater,” he said.
“So all it takes is a few roving males acting as cultural ambassadors to spread their songs [from population to population].”
Singing giants
Although there is still some debate whether male humpbacks’ songs are directed at females or each other, most scientists agree that the song plays a role in reproduction.
Dr Tyack explained: “We have good behavioural observations of singers competing with each other and of females moving to join the singers, so we think it’s associated with mating.”
Dr Patrick Miller from the Sea Mammal Research Unit at the University of St Andrews, UK, said that this study suggested that “some large-scale, previously undetected, factors drive the year-to-year changes in humpback song”.
“We can only begin to speculate what those factors might be, but exploring this will certainly open a new understanding into the lives of these truly cosmopolitan, singing giants.”
source : http://news.bbc.co.uk/earth/hi/earth_news/newsid_9457000/9457855.stm