Researchers dropped a sound recorder into the Baltic Sea and left it there for two months

They recorded 10,000 sounds, all made by the same animal…

Bottlenose dolphins are famously sociable creatures. They usually live in pods where they play, chat and form close friendships with one another.

So when people living around Denmark’s Svendborgsund Channel fell in love with Delle, a male dolphin who had been living alone for years, scientists from the University of Southern Denmark took notice.

Because dolphins are chatty creatures, at least when they are in one another’s company, the scientists wanted to find out whether Delle, as a solitary individual, makes any noise.

The researchers recorded Delle for over two months, using underwater recording equipment.

To their surprise, they picked up a whopping 10,000 sounds.Listen to Delle the dolphin’s solo sounds/Filatova et al.

“Most surprising was that he produced so many sounds while being alone,” Dr Olga Filatova, lead author of the study, tells BBC Wildlife.

“These sounds are traditionally considered communicative, meaning there should be at least two dolphins ‘talking’ to each other.”

When they first looked at their results, the scientists thought that perhaps Delle was chatting to a paddleboarder who spent a lot of time with him, but then they realised that Delle was also chit-chatting away to himself at night, when no humans were present.

What is Delle the dolphin saying?

So what does this solitary chatterbox tell us about dolphin communication?

The researchers suggest a few theories. The first is that dolphins talk to themselves in much the same way that humans do.

We don’t have a good understanding of why we do this but it is a common phenomenon, and not necessarily unique to us.

The second theory is that dolphins involuntarily make noises due to their emotional state, in much the same way humans might say ‘ouch’ if something is painful, even when we are alone.

But it is possible that Delle is making noises for reasons that we simply do not understand yet.

The take-home message is that we don’t know as much as thought we did about dolphin communication.

“If we hadn’t known that Delle was alone, we might have concluded [based on previous research] that a group of at least three dolphins was engaged in various social interactions,” Olga says.

Delle is a well-travelled dolphin. He originates from the Moray Firth, Scotland, where he lived in a pod (and was nicknamed ‘Yoda’) before striking out on his own in Danish waters.

Now, he has moved to the German coast. It seems he is still alone, but hopefully he is chit-chatting away to himself anyway.