A lonely dolphin keeps shouting into the Baltic

Popular Science shares the story of a solo 17-year-old bottlenose dolphin, dubbed “Delle,” who has been spotted off the coast of Denmark for five years, far from any other pods of bottlenose dolphins, vocalizing loudly and constantly into the cold sea and not getting any reply:

Marine biologists from the University of Southern Denmark heard about Delle and noticed a unique opportunity to listen to sounds made by an isolated dolphin in the wild. When they dropped a microphone in the area where Delle traveled for several months, they expected to hear few, if any sounds. They were shocked by what they found.

“Contrary to our expectations, we found that the solitary dolphin was highly vocal,” the researchers wrote in a paper published in the journal Bioacoustics last month.

The researchers believe the surprising findings suggest Delle, starved for social interaction, might be talking to himself. Delle even created multiple “signature” whistles, which pods of dolphins ordinarily use to identify each other.

The researchers listened in on Delle with an underwater microphone for 69 days, between December 8, 2022, and February 14, 2023. Though they initially weren’t expecting much, the researchers say they detected communicative sounds in 35 out of the 69 days.

Delle was quite vocal during those days. In total, researchers say they detected 2,239 whistles, 5,487 low-frequency tonal sounds, 767 percussive sounds, and 2,288 burst pulses. Those burst pulses, which sound like a rapid series of clicks, were particularly interesting because dolphins often emit those sounds as a sign of aggression towards others in their pod. But Delle was all alone. Delle also produced three separate signature whistles. Bottlenose dolphins ordinarily have one unique whistle, which functions akin to a name they use to identify themselves to others.

“I thought we might pick up a few distant whistles or something along those lines,” University of Southern Denmark cetacean biologist and paper lead author Olga Filatova said in a recent interview with Live Science. “I certainly didn’t anticipate recording thousands of different sounds.”

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You can read more about Delle’s underwater muttering and yelling here, in Bioacoustics.