Study unveils the curious case of lonely dolphin talking to himself

Delle is lonely. But he is not quiet.

At the Svendborgsund channel near the Funen Island of Denmark, Delle the dolphin is talking to himself, surprising a group of researchers who studied the aquatic mammal for three months in 2022-2023.

The team of marine biologists from the University of Southern Denmark uncovered the rare finding of the solitary bottlenose dolphin living all by himself in the Baltic Sea and communicating in ways that suggest he is "talking to himself."

Their study, published in Bioacoustics on October 31, 2024, throws new light on how this highly social species copes with isolation.

The dolphin, named Delle by locals, was first spotted five years ago in the Svendborgsund channel, an unusual habitat for bottlenose dolphins. Known for their sociability, dolphins typically live in pods ranging from a few individuals to superpods of over 1,000 members in food-rich areas.

These communities are essential for hunting, mating, and defence, and dolphins form strong, often empathetic and cooperative bonds within them.

However, Delle’s situation defies these norms.

Since his arrival, he has shown no signs of integrating with local harbour animals, including porpoises. Curious about his isolation, researchers lowered microphones into the water and captured over 10,800 vocalisations, including clicks, whistles, and tonal sounds, between December 2022 and February 2023.

A surprising revelation came when researchers identified communication sounds usually directed at other dolphins—Delle appeared to be talking to himself.

Delle made three unique “signature whistles” usually used by dolphins to identify themselves in social groups.

“If we hadn’t known Delle was alone, we might have thought a group of dolphins was interacting,” lead author Olga Filatova from the University of Southern Denmark was quoted as saying in her study.

The researchers propose several theories about Delle’s behaviour. Some sounds may reflect emotional expressions, akin to humans laughing or talking to themselves when alone, while others may help maintain their cognitive functions.

The researchers also noted that Delle continued vocalising even when no humans were present, suggesting his behaviour was not an attempt to interact with people but rather a coping mechanism for isolation.

This behaviour highlights the resilience of dolphins, who rely on social bonds but can adapt when isolated.

A comparison can be drawn to Kylie, a solitary dolphin in Scotland’s Firth of Clyde, who adapted by mimicking harbour porpoise sounds to connect with them.

Delle, however, seems to have taken a different path, relying on self-directed communication to navigate his solitary life.