Such social lives require extensive and constant communication. Vocalisations of dolphins can be divided into two categories: pulsed sounds, such as clicks used for echolocation, and tonal sounds or whistles used for communication with conspecifics. Previous research has shown that bottlenose dolphins each have a signature whistle of changing frequency that helps broadcast their identity.
As well as possessing this signature whistle the dolphins in Cardigan Bay are now thought to have their own ‘dialect’. Speaking on the BBC Wales nature series ‘Wonders of the Celtic Deep’, researchers from the Cardigan Marine Wildlife Centre reported that these dolphins vocalise differently from other dolphins living around the UK and the world. In addition to performing whistles at the same frequency as other dolphin populations, Cardigan Bay dolphins are capable of producing whistles at a much higher frequency of around 40KHz. Such ultra-high frequency whistles can only travel short distances under water reducing the communication range over which they can be used. The purpose of these high frequency whistles is not yet understood, although it probably assists in mate selection or in forming closer social groups.
This is not the first time the bottlenose dolphins of Cardigan Bay have been found to be unique. Research conducted in 2007 by the University of Wales in Bangor and the Shannon Dolphin Foundation in Ireland analysed 1882 whistles from Irish sea dolphins and Cardigan Bay dolphins in order to associate different whistles types to different behavioural categories. The whistles of Irish sea dolphins were significantly shorter and lower in frequency and one whistle type was performed exclusively by dolphins from Cardigan Bay.
