Rare footage of river dolphins helps scientists crack mystery of marine mammal communication

Brazil's Araguaian river dolphin may not be as big of a loner as researchers previously thought.

The river dolphin species commonly referred to as "botos" were first discovered in 2014. Since then, scientists have been eager to learn more about the mysterious creatures. Only 600 to 1,500 are estimated to be in existence in the South American country's Araguaia-Tocantins River system, per a 2014 study published in PLOS One Journal.

Unlike their saltwater siblings, Araguaian river dolphins were considered shy, solitary animals with "little social structure that would require communication," the University of Vermont explained in a news release Thursday.

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But a recent expedition to the Brazilian town of Mocajuba changed researchers' conclusions about the species — and potentially "cracked the code" of how communication has evolved in marine mammals.

Biologists Laura May Collado and Gabriel Melo-Santos of the University of Vermont and the University of St. Andrews in Scotland, respectively, brought a team equipped with underwater cameras and microphones to the Brazilian town of Mocajuba, where botos are more abundant. After analyzing 20 hours worth of recordings of the species, the researchers were able to identify 237 varieties of sounds.

The team's findings were published in the journal Peer J on Thursday.

Brazil's Araguaian river dolphin can make up to 237 distinct sounds.

Brazil's Araguaian river dolphin can make up to 237 distinct sounds. (Mark Carwardine/Barcroft Media/Getty Images)

“We found that they do interact socially, and are making more sounds than previously thought,” Collado said in an online statement. In fact, "their vocal repertoire is very diverse," she added.

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“The majority of studies with Amazonian River dolphins, as well as other river dolphins around the world, reported few sounds used for communication,” Melo-Santos added to Gizmodo. “Some studies would even state that botos had a simple communication system composed by few sound types.”

River dolphins actually use the same signature whistles and noises as their marine counterparts, but they represent different needs.

“It’s exciting; marine dolphins like the bottlenose use signature whistles for contact, and here we have a different sound used by river dolphins for the same purpose,” explained Collado, adding they may even serve the opposite purpose — such as a signal to keep your distance.

They also have a lower tone than the other dolphins, which researchers believe may have changed along with their environment which is reportedly threatened by oil and gas drilling, mining, fishing, pollution, among other issues.

“There are a lot of obstacles like flooded forests and vegetation in their habitat, so this signal could have evolved to avoid echoes from vegetation and improve the communication range of mothers and their calves,” Collado added.

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Since river dolphins, in general, were documented far before other dolphins, the group's findings may indicate their "language" may have contributed to the calls and whistles you hear from marine dolphins today.

In the near future, the researchers hope to study other river dolphin species to see how their communications compare to the botos.

“We can’t say what the evolutionary story is yet until we get to know what sounds are produced by other river dolphins in the Amazon area, and how that relates to what we found,” she says. “We now have all these new questions to explore.”