Melanie Gosling
Environment Writer
PEOPLE have their own names, dolphins have their own whistles.
And in the same way that someone would call out “Jane!” in a crowd to locate the whereabouts of a person called Jane, so a dolphin will whistle the signature whistle of a specific dolphin to find it.
This is one of the findings made by researchers from the University of Pretoria’s Mammal Research Institute and published in this week’s open access journal PLOS ONE.
Although this behaviour had been recorded in captive dolphins and more recently in wild dolphins off Scotland, it is the first time it has been picked up in African dolphins.
Lead scientist Tess Gridley said yesterday: “Research on dolphin acoustic communication in the wild is less common. It was unclear whether African bottlenose dolphins used a similar communication system to those studied in the other localities.
“For the first time we can confirm that African bottlenose dolphins in the wild also use this acoustic communication system when they meet at sea.”
It was only the second time that this behaviour had been picked up in wild dolphins.
Gridley said dolphins had a rich variety of sounds they used in their daily lives to communicate – to find food and echolocation to navigate. They could also learn new sounds and mimic them. Gridley said while this was fairly common among birds, this ability, called vocal production learning, made dolphins special among mammals.
“This ability to learn new sounds is quite unusual in the animal kingdom. Apart from humans, of course, and some birds, there is also some evidence for this in elephants, and good evidence for some whales and seals. But not many. A dog can be made to bark on command, but not to make new sounds.”
Gridley said the dolphins used signature whistles to stay in contact and regroup after they had separated.
“Dolphin groups split and rejoin, and because of that, to be able to tell individuals apart is important.”
Earlier research on dolphins in captivity had shown that each dolphin learnt its distinctive signature whistle in its first year of life.
When stressed, dolphins did not make different sounds, but changed the frequency of their vocalisations and the speed at which they made them.
Gridley’s research, with Simon Elwen, Hannah Kriesel and Aurora Nastasi, was carried out among bottlenose dolphins in Walvis Bay – a different species from the Indo-Pacific dolphins found along the coast from KwaZulu-Natal to Plettenberg Bay.
“Apart from a small population in Angola, this is the only inshore population, from Walvis Bay right around South Africa to about Zanzibar. What is worrying is that there are only about 100 in Walvis Bay, which has lots of tourist boats and plans to construct a port. We’re really concerned for this population because of the threats they face – particularly the increase in man-made noise.”