The findings of a recent study, published in the journal Bioacoustics on reveal a surprising picture of a solitary bottlenose dolphin named Delle living in the Baltic Sea. Researchers recorded over 10,800 vocalizations from Delle between December 2022 and February 2023, including sounds typically used for communication among dolphins, raising questions about animal communication and the need for social interaction.
Delle has been residing in the Svendborgsund strait, south of Funen Island in Denmark, since 2019—a rare phenomenon in this part of the Baltic Sea, which is far outside the typical range of bottlenose dolphins. Living alone in these uncharted waters, Delle has no companionship from other dolphins nearby and is forced to navigate this non-natural habitat on his own.
The study was conducted by a team of scientists led by cetacean biologist Olga Filatova at the University of Southern Denmark. Initially, the researchers installed underwater recording devices in late 2022 to study the impact of Delle on local harbor porpoises. Between December 2022 and February 2023, they monitored Delle's vocalizations, collecting a total of 10,833 sounds over 69 days, including 2,291 whistles, 2,288 burst pulses, 5,487 low-frequency tonal sounds, and 767 percussive sounds.
The researchers were astonished by the volume and complexity of the sounds produced by the solitary dolphin. "I certainly didn't expect to record thousands of different sounds," said Filatova, as reported by Mundo. "If we hadn't known that Delle was alone, we might have concluded that a group of at least three dolphins was engaged in various social interactions,” she added.
By analyzing the recordings, the biologists discovered that Delle uses sounds typically associated with communication among peers. Some of these vocalizations usually require a second dolphin to make sense, highlighting the unexpected complexity of his vocal behavior. "These sounds are traditionally considered communicative, which implies that there should be at least two dolphins interacting. But Delle was completely alone," Filatova said.
One possible explanation is that the sounds are involuntary emissions reflecting an emotional state, such as anxiety or frustration, in response to his solitude. This is akin to humans who laugh when reading something funny even when no one is around.
Another hypothesis is that, like humans, dolphins have a strong instinct for social interaction, and solitude might lead Delle to 'talk' to himself as if seeking company. Humans often talk to themselves without an interlocutor, as a form of self-regulation or to satisfy a need for social communication. This observation raises fascinating questions about dolphin psychology and evolution.
A third possibility is that Delle is trying to attract the attention of other dolphins, although this seems less likely after three years of living in solitude in the area. Filatova noted that given Delle's extended time in the region, he would likely know by now that no other dolphins are present.
Some of Delle's vocalizations occurred at night when there were no humans nearby, eliminating the possibility that his vocalizations were a direct response to human activity. The researchers also noted that bottlenose dolphins are social animals that prefer to live in groups and that they have signature whistles unique to each individual, functioning like names among humans. Dr. Filatova explained that bottlenose dolphins have signature whistles, which function like unique names for each individual.
"Their vocal behavior is consistent with the highly vocal nature of dolphins," noted Thea Taylor from the Sussex Dolphin Project, as reported by Mundo. Taylor stated to Live Science, "They depend on sound to hunt, explore the environment, and communicate over long distances".
This article was written in collaboration with generative AI company Alchemiq