A lone dolphin in the Baltic Sea has been recorded talking to himself, sparking curiosity among researchers.
They speculate that he might be expressing loneliness, potentially calling out in hopes of finding some friends.
Bottlenose dolphins (Tursiops truncatus) are known to be social animals that live in pods. But in September 2019, a single dolphin started hanging around the Svendborgsund channel, which is located south of Funen Island, Denmark, an area that is outside of the usual range of the species.
Locals know the dolphin as Delle. No other dolphins were seen nearby. Researchers deployed underwater recording devices to observe how the solitary dolphin's presence affected porpoises near the harbor. They were shocked when they heard how noisy Delle was.
"Out of curiosity, I decided to add a recorder that captures actual sounds," said Olga Filatova, the lead author of the study and a cetacean biologist at the University of Southern Denmark.
"I thought we might pick up a few distant whistles or something along those lines. I certainly didn't anticipate recording thousands of different sounds."
Over the course of 69 days between December 8, 2022, and February 14, 2023, the researchers detected a total of 10,833 sounds.
Many of them were related to communication and included 2,291 whistles, 2,288 burst-pulses, 5,487 low-frequency tonal sounds, and 767 percussive sounds.
Burst-pulses are a series of rapid-fire clicks sometimes associated with aggression. Among these noises, the dolphin also produced three distinctive whistles.
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