Rare video footage of Araguaian river dolphins. Credit: Paulo Castro
The Araguaian river dolphin of Brazil was discovered as a unique species five years ago and is a fascinating, yet poorly understood aquatic creature. New research shows that these dolphins produce surprising sounds ̵
1; an important indication of how and why dolphins have developed the ability to communicate.
The Araguaian river dolphins, also known as botos, were first identified in 2014. Botos live exclusively in the Amazonas, Orinoco and Tocantins river basin of South America, where they hunt for fish with their long beaks.
These dolphins are considered evolutionary relics and have previously deviated from other whales (a family that includes dolphins and whales) than other dolphins. Due to their unique position within the desert tree, scientists can study these creatures to better understand the ancestors of marine dolphins, such as the porpoises. By studying botos in the wild, scientists can gain new insights into the behavior of certain dolphin behaviors, such as their communication skills. For example, biologists want to know if these iconic clicks and whistles came about as a result of river or marine life.
Botos are notoriously elusive. In contrast to marine animals and their dramatic fractures, botos do not excite when they fly. They are lonely and shy and live in small social groups. These dolphins are critically endangered, of which only 1,000 may be left. Little is known about their ability to produce sounds or to communicate with each other, but research done several years ago suggests that they can produce sounds such as clicking, whistling, snapping, and other sounds. In addition, not much was known.
"The majority of studies with Amazon river dolphins and other river dolphins around World reported few sounds used for communication, "said Gabriel Melo-Santos, the lead author of the new study and a marine biologist at the University of St. Andrews, in an email to Gizmodo. "In some studies it was even claimed that botos had a simple communication system with few sound types."
Coincidentally, however, there is a group of botos in the Tocantins River in the city of Mocajuba, Brazil, who have become accustomed to humans. The people of this city feed the dolphins on a fish market along the river. Melo-Santos visited with the biologist Laura May-Collado from the University of Vermont this market to investigate this particular population. Their new research, published today in PeerJ, shows that river dolphins from Aragua are capable of producing hundreds of different sounds for communication.
Using underwater microphones and cameras, the researchers recorded the sounds and behavior of the dolphins. Genetic samples were taken to determine relationships. Almost 400 tones were recorded, which researchers classified into different types, including 13 types of tone sounds and 66 types of pulsed calls.
"It was a big surprise when we discovered more than 200 sound types. Our results show that there is more to discover, "said Melo-Santos. "Interestingly, we discovered that the most commonly produced sounds seem to play an important role in mother-calf communication."