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A solitary bottlenose dolphin in the Baltic Sea has been observed generating a significant number of vocal sounds, raising questions about the implications of its isolation. The dolphin, known locally as Delle, was first detected in the Svendborgsund channel near Funen Island, Denmark, in 2019. Traditionally, bottlenose dolphins are social creatures that live in groups, yet Delle has been seen alone with no other dolphins in the vicinity.
The University of Southern Denmark utilized underwater recording devices to study Delle’s influence on nearby harbour porpoises. These recordings revealed an astonishing total of 10,833 individual sounds captured over a span of 69 days from December 8, 2022, to February 14, 2023. Dr. Olga Filatova, a leading cetacean biologist involved in the research, indicated that among the variety of sounds recorded were whistles and tonal noises, typically associated with social exchange among dolphins, highlighting the unusual nature of Delle’s vocalizations.
Analyzing the Sound Data
The analysis of the vocal patterns showed that Delle produced 2,291 whistles and 2,288 burst-pulses—sounds that can signal aggression or excitement. Notably, three specific whistles were recognized as “signature whistles,” distinct calls used by dolphins to identify themselves. These results, published in the journal Bioacoustics on October 31, initially led researchers to think that other dolphins might be present in the area. However, the confirmation of Delle’s solitary status compelled them to reassess these interpretations.
Exploring the Reasons Behind the Vocalizations
Experts propose that the wide range of sounds might reflect Delle’s attempts to reach out to potential companions or could signify emotional expressions, akin to humans laughing when alone. Dr. Filatova pointed out that it seems improbable that Delle was actively seeking out other dolphins, since its prolonged presence in the area has been marked by a clear absence of any companions.
This research emphasizes the need for deeper insights into the behavior of solitary dolphins. Thea Taylor, the Managing Director of the Sussex Dolphin Project, remarked on the significance of these findings in expanding the understanding of dolphin emotions and behaviors, noting that solitary dolphins remain an overlooked subject in research. Delle’s case exemplifies the intricacies of dolphin communication, prompting researchers to further explore the reasons behind such vocalizations in solitary settings.
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