Signature information and individual recognition in the isolation calls of Amazonian manatees, Trichechus inunguis (Mammalia: Sirenia)

Abstract

Acoustic signals are assumed to form the basis of manatee communication. Empirical evidence of individual vocal recognition has been reported. If manatees can recognize one another by acoustical means, it should be possible to identify individual vocal patterns. We recorded vocalizations of 14 individually housed Amazonian manatees and then digitized selected vocalizations, allowing seven variables to be measured and subjected to multivariate statistical treatment. Discriminant function analysis indicated that individuals can be separated on the basis of variables related to the fundamental frequency and signal duration. We observed significant differences in the vocal patterns between sexes and age classes. Females tended to have greater fundamental frequency and shorter note duration than males. Calves had shorter note durations and greater values for the fundamental frequency range than subadults and adults. An inverse relationship between total body length and fundamental frequency range suggests that the fundamental frequency becomes more defined as the animal ages. The similar individual patterns in the vocalizations of a mother and calf pair are discussed. Individual recognition by Amazonian manatees according to their vocal patterns is suggested through a preliminary playback experiment.