Individual distinct vocalisations in Amazonian manatees Trichechus inunguis [abstract]

R. S. Sousa Lima, A. P. Paglia and G. A. B. Fonseca (2002). Individual distinct vocalisations in Amazonian manatees Trichechus inunguis [abstract]. Bioacoustics, Volume 13 (1): 90 -91

Amazonian manatees have historically been exploited in Brazil but there is little information on population status and trends. The difficulty of tracking individuals in turbid water habitats restrains the assessment of behavioural characteristics, which in turn could be helpful in determining some key parameters about their conservation status. Currently, acoustic signals are assumed to form the basis of manatee communication, for which prior empirical evidence has been reported. Therefore, if manatees can recognise each other by acoustical means, it should be possible to identify individual vocal patterns. Vocalisations were recorded of 14 captive Amazonian manatees, temporarily and individually housed. The vocalisations were digitised and seven variables were recorded. These were subjected to multivariate statistical treatment. Principal Components Analysis grouped the data indicating that some individuals could be distinguished on the basis of variables related to the fundamental frequency of vocalisations (axis 1 of the PCA). We have also observed a significant difference in axis 1 between sexes, with a tendency of females to have higher fundamental frequency values than males. No difference was observed between different age classes in axis 1 of the PCA. Axis 2 of the PCA was positively related with the signal duration, isolating a mother and calf pair with greater signal duration values than the others. An inverse relation between body size (total body length) and the range of the fundamental frequency was verified. This study reinforces the possibility of identifying individual manatees by their vocal patterns, hence making bioacoustics a useful tool for behavioural and social studies, in addition to providing needed information on conservation strategies for the species.