Lack of species-specific vocal recognition in Amazonian manatees: Trichechus inunguis

Abstract

Playback experiments were conducted in order to test for the existence of species-specific vocal recognition in Amazonian manatees. The animals were isolated in pools while acoustic stimuli were played from a tape recorder and transmitted underwater through a loudspeaker. Nine animals were monitored for response to playback vocalizations from eighteen different individuals, nine from each species (Trichechus inunguis and T. manatus manatus). No significant differences were detected in the response of manatees exposed to the different stimuli. Only the time spent close to the speaker was greater when the animals were exposed to conspecific vocalizations (ρ=0.375). This result suggests that Amazonian manatees cannot recognize differences between their own and another manatee species’ vocalization. The methodology was also tested and no difference in the response of animals exposed to silence or to tape hiss (blank tape used as control) was found. Testing the response to the presence or absence of vocalizations, significant differences were found in time elapsed between the playback and the response (ρ<0.001) and in the time spent next to the speaker (ρ=0.032), confirming their great ability to perceive sounds underwater. [Work supported by FBPN, MacArthur Foundation, CI, FINEP, MCT/PPG7 and CNPq.]