Response to playback test in the captive Amazonian manatees (Trichechus inunguis) in Brazil

Abstract

Previous studies suggested that manatee calls were primarily for communication and not for navigational purposes. In this study, the vocal response of captive Amazonian manatees to playbacks of several acoustic stimuli was investigated. Experiments were conducted using nine captive Amazonian manatees at the National Institute of Amazonian Research (INPA), Brazil, in 2014. All manatees, except one, are orphan calves rescued from the illegal hunting or incidental catch. They were kept in the outdoor pool with a group of 2-3 individuals, which are considered to be related. Manatees were exposed to five different playback stimuli: a recorded vocal from a related manatee, a recorded vocal from an unrelated manatee, a synthesized constant frequency based on the fundamental frequency of a related manatee vocal, a synthesized sound which entirely different from manatee vocal, and silence. A total of 58 playback sessions was conducted and 22,590 calls were recorded. While manatees showed inter-individual variability in the response to the playback stimuli, they tended to produce more vocalization during the playback of the related manatee vocal. They also tended to vocalize more to the playback of the constant frequency sound. Some individual showed strong reactions; touching or staying near the speaker during the experiment.