Lonely dolphin in Baltic Sea found to be talking to himself

19 Nov 2024, 14:59 by Bob Yirka

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Timing and context of the occurrence of communicative sounds of the dolphin (dark gray indicates nighttime, light gray indicates twilight, white indicates daylight). Credit: Bioacoustics (2024). DOI: 10.1080/09524622.2024.2422092

A team of marine biologists at the University of Southern Denmark has discovered a solo male dolphin living in the Baltic Sea, who appears to be talking to himself. In their paper published in the journal Bioacoustics, the group describes how they analyzed underwater sound recordings that captured thousands of sounds made by the dolphin and what they learned from them.

Five years ago, local people living on the shores of Svendborgsund channel, in the Baltic Sea, in Denmark, noticed that a solitary male bottlenose dolphin had arrived and had apparently made the channel its home. The find was rare, as such dolphins do not typically live in that area, and dolphins are widely known to live in pods.

Soon, the dolphin attracted the attention of marine biologists who wanted to understand why a dolphin would choose to make such a place his home. They noted that it was not likely that the dolphin had befriended the local harbor porpoises. Eventually, they lowered a microphone into the water to find out if the dolphin, which the locals had named Delle, was making any noises.

To their surprise, the research team found that Delle was making a lot of noises—they detected 10,833 voicings from December 2022 to February 2023. In listening to the recordings, they found that Delle was making a whole range of sounds, from clicks, to whistles, to sounds that have been associated with aggressive behavior in dolphins.

Also among the recordings were sounds that have been associated with communications between dolphins—a sign that the dolphin was talking to itself. Delle was also making low-frequency tonal sounds along with percussive sounds, which the researchers believe help in navigation and finding food.

The researchers noted that the dolphin continued talking when no humans were around, showing it was not trying to talk to them. They suggest it is possible some of the voicings are related to emotional outbursts, similar to a human being laughing at something despite being alone. They also suggest it is possible the creature is simply lonely and talking to itself is a means of distraction.

More information: Olga A. Filatova et al, Dolphin self-talk: unusual acoustic behaviour of a solitary bottlenose dolphin, Bioacoustics (2024). DOI: 10.1080/09524622.2024.2422092