Do the Shannon dolphins have a local dialect ?
Sound is very important to dolphins living in the sea as visibility underwater is often very poor. Dolphins produce a variety of vocalizations including clicks, whistles, barks, and groans to navigate and communicate with each other. Each dolphin is thought to have its own distinctive whistle, a signature whistle, by which other dolphins can recognize it.
Work carried out on the bottlenose dolphins in the Shannon estuary by the Shannon Dolphin and Wildlife Foundation is attempting to record and categorise the different types of whistles they produce. We are trying to build up a catalogue of the different whistle types they use and trying to associate them with behaviour such as foraging, resting, socialising or whether the group have calves present. Essentially we are building up what is like a dictionary of vocalisations they use or sounds they make.
As part of a recent research project, student Ronan Hickey digitised and analysed a total of 1,882 whistles from the Shannon dolphins and those from bottlenose dolphins in Cardigan Bay in Wales. He separated them into six fundamental whistle types and 32 different categories. Of the categories, he found most were used by both populations of dolphins, but eight whistle types were only produced by the Shannon dolphins.
The sounds are captured via a hydrophone deployed off Kilcredaun Point near Carrigaholt in west Clare. The signal is relayed to a nearby cowshed, which houses a computer. The hydrophone is sampled every hour and recordings stored to an external hard drive. Recordings are screened for whistles, which are extracted and described mathematically using MATLAB.
A dialect is a unique set of discrete calls made by an individual dolphin and its group members. If the Shannon dolphins are producing vocalidsations, unique to the Shannon estuary, this may indicate that the Shannon dolphins have a different “dialect” compared with Welsh or other dolphin populations. More recordings and analysis are required to explore this hypothesis in more detail but as the dolphins at both sites are resident and live in different physical environments it is not improbable that they have evolved distinctive sets of vocalizations or “dialects”.
In Canada, researchers have discovered that in resident pods of killer whales, each whale has the same set of calls, or dialect, as other pod members. The only other mammals known to have true dialects are humans, some monkeys, and the sperm whale. Groups of whales that share the same "dialect" are related to each other.
This project is called “Soundwaves” and has been developed in collaboration with the Hydralics and Maritime Research Centre at UCC and was funded by the Vodafone Group Foundation.
Hickey, R. (2005) Comparison of whistle repertoire and characteristics between Cardigan Bay and the Shannon estuary populations of Bottlenose dolphins (Tursiops truncatus) with implications for passive and active survey techniques. School of Biological Sciences, University of Wales, Bangor
Berrow, S.D., O’Brien, J. & Holmes, B. (2006) Whistle production by bottlenose dolphins Tursiops truncatus in the Shannon estuary. Irish Naturalists' Journal 28(5), 208-213.
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