Humans greet each other by name. Bottlenose dolphins do much the same – they just each whistle their own tune.

“And for the first time we can now confirm that African bottlenose dolphins in the wild also use this acoustic communication system when they meet at sea,” explains Dr Tess Gridley, a post-doctoral fellow at the University of Pretoria’s Mammal Research Institute (MRI) and the lead scientist of a study on the signature whistles of wild bottlenose dolphins (Tursiops truncatus) from Namibia.

The study, co-authored by Dr Simon Elwen, also from the MRI, Hannah Kriesel and Aurora Nastasi is published in this week’s PLOS ONE, an open access journal.

Sound communication

Most dolphin species rely on a rich repertoire of sounds in their day to day lives. They use sound to find food and navigate (echolocation) as well as communicate with each other. Dolphins can learn new sounds and can quickly mimic novel sounds that they hear. Although fairly common among many bird species and humans, this ability, termed vocal production learning, makes them quite special amongst mammals.

The vast majority of global research on bottlenose dolphin acoustic communication has been conducted in captivity. These studies have shown that each animal learns its own individually distinctive whistle, termed a ‘signature whistle’, in the first year of life and that they use the same whistle throughout life. Recent research in Scotland has shown that signature whistles are exchanged by groups of dolphins when they meet at sea and that signature whistles are used to address each other – somewhat like a name in human society.

However, research on dolphin acoustic communication in the wild is less common and until now it was unclear whether African bottlenose dolphins use a similar communication system to those studied in other localities.

Drs Gridley and Elwen conduct research on whales and dolphins in Namibia and run the Namibian Dolphin Project. Since 2009 they have been investigating the fascinating lives of a small population of bottlenose dolphins inhabiting Walvis Bay, located on the central Namibian coast.

“The research that is published this week outlines some of the first results of this study. It demonstrates that individual dolphins are likely to be using unique signature whistles throughout their lives, probably to keep in contact and address each other.

“This is the first time that signature whistles have been identified from any population of this species inhabiting African waters, and it is only the second wild population of this species where the features of the signature whistles have been described in detail,” says Dr Gridley.

The research was the Master’s thesis of their student Ms Hannah Kriesell, who graduated earlier this year from the University of Goettingen in Germany.

More than 79 hours of recordings, collected over 4 years in the presence of dolphins, were used to generate a catalogue of 28 signature whistles – around one quarter of the population in Namibia. Evidence for two voice whistle production (imagine if you could whistle two different tunes at the same time) was also found. According to Dr Gridley, two-voice sound generation occurs in some bird species and may be a way to make calls more complex – which can be a good thing if you want a really unique signature call.

The study also shows that the number of different signature whistles recorded increased when group sizes were larger and when calves were present – something you might expect if signature whistles are used to address each other and help maintain contact between animals, particularly between mothers and calves.

The outcomes of this research provide an important stepping stone for future studies into how sounds are used and whether human activities are affecting the communication of our whale and dolphin populations. This is particularly important in Walvis Bay where the impacts of human activity threaten the small bottlenose dolphin community. Researchers from the MRI Namibian Dolphin Project hope to monitor changes in dolphin behaviour related to such potential stressors. 

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For further information, please contact Dr Tess Gridley:
nam.dolphin.project@gmail.com
+27 21 788 1206

or visit the website:
www.namibiandolphinproject.com

To download a PDF of this article please follow the link:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0106317