A solitary bottlenose dolphin in the Baltic Sea has raised eyebrows in the scientific community with its unusual behavior. Known locally as Delle, the dolphin has been residing in the Svendborgsund channel, south of Funen Island in Denmark, since September 2019. While bottlenose dolphins are typically social animals that live in pods, Delle’s lone presence in the area, which falls outside the species’ usual range, has intrigued researchers.
Researchers typically avoid documenting the sounds of solitary dolphins, considering them outcasts who produce few noteworthy noises. However, a group of scientists decided to break from tradition by deploying underwater recording devices to monitor Delle’s behavior. The study, which took place between December 2022 and February 2023, was an attempt to understand the dolphin’s unique communication in isolation.
What began as a modest attempt to record a few distant whistles turned into a groundbreaking discovery. Lead author Olga Filatova expressed her surprise, saying, “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.”
The study found that Delle produced a remarkable 10,833 sounds, including a variety of tones such as 2,291 whistles, 2,288 burst pulses, 5,487 low-frequency tonal sounds, and 767 percussive noises. Most intriguing was the identification of three distinct types of stereotyped whistles, which deviated from the usual patterns seen in other dolphins. Additionally, the researchers found three different biphonic sound categories, which involved combinations of various sound components.
Bottlenose dolphins typically use signature whistles, which function similarly to names, allowing them to maintain group cohesion. The fact that Delle was alone makes these sounds particularly puzzling. “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,” Filatova explained.
While the reasons behind Delle’s extensive vocalization remain uncertain, two theories have emerged. One suggests that the dolphin might have been producing involuntary sounds, similar to how humans might laugh at something funny when alone. Another possibility is that Delle was attempting to attract other dolphins to the area, possibly in an attempt to reconnect with his species.
Delle’s unusual behavior has sparked both scientific curiosity and speculation. Whether these sounds are a cry for companionship or a quirk of isolation, the findings have opened a new window into the complexities of dolphin communication. Further research is expected to explore whether Delle’s actions are common among solitary dolphins or a unique anomaly.
