A solitary dolphin living in the Firth of Clyde, Scotland, has adapted its vocalization in order to communicate with the estuary's resident harbor porpoises. That is according to research led by Mel Cosentino, a PhD student at the University of Strathclyde, which is currently awaiting peer-review.
"If further analysis shows this to be the case, it would be the first time a common dolphin, either in captivity or the wild, has demonstrated an ability for production learning, where it has learned to imitate another species," Cosentino explained in a statement.
The dolphin in question has been nicknamed Kylie. He has been living on his own around a navigational buoy between Fairlie and Cumbrae for at least 17 years, presumably after getting lost from his pod. The area is not normally frequented by short-beaked common dolphins like Kylie, so it appears he has adapted his "speech" to communicate with a group of cetaceans a little bit closer to home – in this case, the estuary dwelling harbor porpoise, which is found in temperate waters across the northern hemisphere.
To examine alterations in Kylie's acoustic repertoire, David Nairn and others at Clyde Porpoise CIC recorded audio clips of dolphin and porpoise vocalizations using a pair of underwater microphones, which were then extracted using a custom-built algorithm. This allowed Cosentino to analyze the recordings and compare the noises Kylie made when he was interacting with porpoises to those made when he was alone.
Research on common dolphin echolocation clicks (used for hunting and navigating) may be limited but from what we know, they tend to stay below a peak of 100 kilohertz (KHz). To communicate, dolphins may also whistle and bark. In comparison, harbor porpoise vocalizations are restricted to a narrow-band of high-frequency echolocation clicks used for hunting, navigating and communicating, which can reach a peak frequency as high as 130KHz.
Interestingly, when Kylie was in the presence of harbor porpoises, he was often recorded making clicks of more than 100KHz. What's more, some of his clicks were over 130KHz. And this all occurred far more frequently when he was with the porpoises than when he was not, suggesting he was adapting his vocalizations for the porpoises' benefit. While he was also recorded making buzzes, no whistles were reported whereas there were no differences noted in the porpoise acoustic repertoire.
More audio clips of Kylie alone are needed to back these findings before the research can be submitted for peer-review but the results so far do seem to suggest socialization with the harbor porpoises are influencing his speech – and it wouldn't be the first time an individual cetacean has adapted its acoustics to benefit its interspecies neighbors.
"Several cetacean species, such as bottlenose dolphins, belugas, and killer whales, have the ability to change their acoustic repertoire as a result of interactions with other species," Cosentino explained, adding that it tends to be witnessed more in captivity than in the wild. For example, a 2014 study revealed a group of captive orcas had adapted their speech patterns to communicate with a nearby group of bottlenose dolphins.
Neither would it be the first instance of a wild dolphin interacting with another species. A group of dolphins in Hawaii have been observed "riding" humpback whales, while another in Brazil have been reported collaborating with local fishermen.