Short-beaked dolphin ‘talking’ with harbor dolphin

The Firth of Clyde, a large saltwater bay on the west coast of Scotland, is home to thousands of harbor dolphins and a wild dolphin named Kylie. Researchers haven’t observed Kylie with another short-beaked dolphin (Delphinus delphis) for at least 14 years, but she’s not alone. On clear days at Clyde, dock-goers can sometimes spot Kylie swimming with the harbor dolphin (Phocoena phocoena), which is a relative two-thirds the size.

New research published in the journal Bioacoustics suggests that Kylie is much closer to harbor dolphins than scientists imagine. While short-snouted dolphin sounds include a wide variety of calls like clicks, whistles, and vibratoes, Kylie doesn’t whistle. Instead, it “talks” more like a harbor dolphin, communicating through bursts of high-pitched clicks. Research suggests Kylie may be trying to communicate with harbor dolphins, an example of the rich interaction between marine mammals, according to behavioral expert Denise Herzing.

Years ago, Clyde’s only short-beaked dolphin appeared in Kyles of Bute’s mouth, so the locals called him Kylie. No one knows where the dolphin came from or why it was alone, said David Nairn, founder and director of Clyde Porpoise, an organization dedicated to the study and protection of marine mammals.

Some dolphins live alone after being separated from their herd by storms, human activities, or orphanages. To learn more about Kylie’s relationship with harbor dolphins, Nairn borrowed an underwater tuner and tugged the back of her sailboat Saorsa. Nairn recorded audio of several encounters between Kylie and the harbor dolphins between 2016 and 2018.

Mel Cosentino, a PhD student at the University of Strathclyde in Glasgow, contemplates thousands of cephalopod clicks from audiotapes. While short-beaked dolphins whistle almost regularly, harbor dolphins never do. Instead, they use only narrow band high frequency clicks (NBHF), with 8 – 15 peak amplitudes at 130 kiloherts. To hear the NBHF click, the researchers had to play the tape 100 times slower.

From the recordings, Cosentino identified the standard low-frequency clicking sound of a short-beaked dolphin. But even when Kylie was alone, Cosentino detected clicks with at least eight amplitude peaks at 130 kilohertz, the frequency harbor dolphins normally use to communicate with each other. In other words, Kylie talks like a harbor dolphin. The team also found that he never whistled like a typical short-beaked dolphin.

Cosentino observed that the exchanges between Kylie and harbor dolphins were as rhythmic as between members of the same species. They take turns talking and rarely overlap. However, the research team is not clear on how much meaningful information is contained in the sound created by Kylie.

a khang (Based on National Geographic)

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