This is rare video footage of Araguaian river dolphins. The dolphins are swimming in the Araguaia River near a fish market in the Brazilian town of Mocajuba that the animals regularly visit to be fed by the people shopping there. Normally they are hard to find and study. Researchers from the University of Vermont and University of St. Andrews discovered that the dolphin species, which was thought to be solitary and quiet, can actually make hundreds of different sounds, a finding that could help uncover how communication evolved in marine mammals.A number of vocalization are heard in the video. The clicking sounds are used for echolocation. Audible midway through the video is a short, two-part call baby dolphins make when they were approaching their mothers. Bubbles from its blowhole are visible as it produces the sound. The video is a supplement to the paper published in PeerJ.