Gender, Age, and Identity in the Isolation Calls of Antillean Manatees (Trichechus manatus manatus)

Abstract: Empirical evidence of individual vocal recognition has been reported for the Amazonian manatee (Trichechus inunguis) and the West Indian manatee (T. manatus). Underwater vocalizations of 15 Antillean manatees (T. m. manatus) were recorded to verify if this subspecies also conveys individual information through their calls. The isolation calls selected for analysis were digitized to measure eight different variables. Individual vocal patterns were analyzed within two age classes (calves and others) and between sexes. Discriminant function analysis for each age class grouped vocalizations by individual, based on variables related to the fundamental frequency and call duration. Female calls were longer in duration and presented a higher fundamental frequency but lower peak frequency values than males. Calves had significantly higher values for all eight acoustic variables measured with respect to frequency and time. Higher values for all frequency parameters in calf calls and the inverse relationship between total body length and peak frequency suggests that younger, smaller animals emit higher frequency sounds. Furthermore, higher values obtained for the fundamental frequency range of calves and the inverse relationship of this variable with total body length suggest that the fundamental frequency becomes more defined as the animal ages. Vocal learning and genetic inheritance are discussed based on the analyses of vocal patterns among related individuals. In addition to facilitating individual recognition as a possible factor in Antillean manatee social interactions, vocal identity provides a potential means of estimating the size and structure of sirenian populations.

Key Words: Sirenia, manatee, Trichechus manatus manatus, calls, sounds, vocalization, gender differences, age differences, vocal identity, communication

Document Type: Research article

DOI: 10.1578/AM.34.1.2008.109

Page Numbers: 109-122

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