A bottlenose dolphin residing alone in the Baltic Sea has been documented producing thousands of vocalisations, potentially as a result of loneliness. Known locally as Delle, this dolphin was first noticed in the Svendborgsund channel near Funen Island, Denmark, in 2019. Bottlenose dolphins typically thrive in social pods, but no other dolphins have been seen in the area.
The University of Southern Denmark deployed underwater recorders to monitor the impact of Delle’s presence on local harbour porpoises. Unexpectedly, 10,833 sounds were recorded over 69 days between December 8, 2022, and February 14, 2023. Dr Olga Filatova, cetacean biologist and lead researcher, reported hearing an extensive range of sounds, including whistles and tonal noises. These sounds are often associated with social interactions among dolphins, yet Delle was entirely alone.
Unpacking the Recordings
Among the captured vocalisations were 2,291 whistles and 2,288 burst-pulses—clicks often linked to aggression or excitement. Delle also produced three distinctive whistles resembling “signature whistles”, unique sounds used by dolphins as individual identifiers. These findings, detailed in the journal Bioacoustics on October 31, led researchers to initially speculate that multiple dolphins might be present. However, Delle’s solitary state ruled out such assumptions.
Possible Explanations for the Vocalisations
The sounds may indicate attempts to connect with others or might simply reflect involuntary expressions linked to emotions, similar to humans laughing while alone. Dr Filatova suggested it is unlikely that Delle was calling other dolphins, as his years in the area would have revealed the absence of companions.
The study highlights a gap in understanding solitary dolphins’ behaviour. Thea Taylor, Managing Director of the Sussex Dolphin Project, noted the potential for these findings to provide insights into dolphin emotions and behaviour, stressing that solitary individuals remain under-researched.
Delle’s case underscores the complexity of dolphin communication, with researchers aiming to uncover the motivations behind such vocal patterns in isolated circumstances.