Florida manatees (Trichechus manatus) produce five broadly defined call types (squeaks, squeals, high squeaks, chirps, squeak‐squeals) but their use in social and nonsocial settings is unclear. The goal of this study was to investigate whether call categories and structure of manatee vocalizations varied with behavior. Multiple hydrophones were used to record vocalizations in four different environments and broad behavioral states. Vocalizations recorded from resting, cavorting, stressed, or feeding wild animals were subjected to mixed linear effects models to test whether vocalizations produced varied with behavior and calf presence. Measures of duration, entropy, and frequency modulation were extracted from vocalizations to investigate if structural parameters differ among behaviors. Although all five call categories were recorded, results suggest manatees vocalize using primarily three call types and vary the structure of the call based on behavior. High squeaks were correlated with calf presence. High entropy squeals were proportionally higher during cavorting suggesting they may be related to a heightened state of arousal. Squeaks were the dominant call type produced and were longer in duration and higher in frequency modulation when animals were stressed. This research provides a foundation for comparative studies on vocal behavior for the Florida manatee as well as studies on related species.

The vocal repertoire for the Florida manatee is quantitatively categorized from a sample of 1114 calls recorded from 3 different manatee habitats in Florida. First, manatee vocalizations were categorized into five call categories based on visual inspection of spectrograms and following descriptions provided in previous studies. Second, based on measurements of 17 acoustic parameters, the subjective classification scheme was validated using classification and regression trees (CARTs) and model-based cluster analysis paired with silhouette coefficients. CART analysis revealed that these five broad call categories can be successfully distinguished based on correct classification scores of 41.6%–62.5%. Silhouette coefficients determined that the manatee vocal repertoire is highly intergraded. This study supports and expands upon existing subjective categorization schemes by providing a quantifiable methodology for describing the Florida manatees' vocal repertoire. These findings contribute to the increasing number of studies suggesting many animal species vocal repertoires contain graded call types.

Antillean manatees produce vocalizations reported to be important for communication, but their vocal behavior throughout their geographic range is poorly understood. A SoundTrap recorder (sample rates: 288/576 kHz) was deployed in Belize to record vocalizations of wild manatees in a seagrass channel and of a young rehabilitated and released manatee in a shallow lagoon. Spectral analysis revealed broadband vocalizations with frequencies up to 150 kHz and a high proportion of calls with ultrasonic components. Ultrasonic frequency components appear prevalent in their vocal repertoire and may be important to manatee communication.

Even among the understudied sirenians, African manatees (Trichechus senegalensis) are a poorly understood, elusive, and vulnerable species that is difficult to detect. We used passive acoustic monitoring in the first effort to acoustically detect African manatees and provide the first characterization of their vocalizations. Within two 3-day periods at Lake Ossa, Cameroon, at least 3367 individual African manatee vocalizations were detected such that most vocalizations were detected in the middle of the night and at dusk. Call characteristics such as fundamental frequency, duration, harmonics, subharmonics, and emphasized band were characterized for 289 high-quality tonal vocalizations with a minimum signal-to-noise ratio of 4.5 dB. African manatee vocalizations have a fundamental frequency of 4.65 ± 0.700 kHz (mean ± SD), duration of 0.181 ± 0.069 s, 97% contained harmonics, 21% contained subharmonics, and 27% had an emphasized band other than the fundamental frequency. Altogether, the structure of African manatee vocalizations is similar to other manatee species. We suggest utilizing passive acoustic monitoring to fill in the gaps in understanding the distribution and biology of African manatees.