Manatee calf call contour and acoustic structure varies by species and body size

Abstract

Vocal activity and signal characteristics of mammals are driven by several factors that result in both stability and plasticity over multiple time scales. All three extant species of manatee communicate with several calls that are especially important for maintaining contact between cows and calves. Determining if calf calls differ across manatee species will provide insights into the evolution of species-specific acoustic communication traits. We investigated the interspecific differences in the vocalizations of calves of Amazonian manatees (Trichechus inunguis) and the two subspecies of the West Indian manatee (T. manatus). Vocalizations of individual calves were recorded in rehabilitation centers in Brazil, Puerto Rico, the United States, and Mexico. The acoustic structure of calls produced by manatee calves varied between species and with body size. Amazonian manatee calves produced shorter calls with multiple notes at higher frequency while West Indian calves produced modulated calls that were lower in frequency and longer in duration. Smaller West Indian calves produced frequency modulated, hill-shaped calls that flattened with an increase in body length. Our results provide evidence for divergence in the ontogeny of vocalizations across T. manatus and T. inunguis and suggest variation in body size contributed to the evolution of differences in the characteristics of their calls.

Antillean manatee calves in captive rehabilitation change vocal behavior in anticipation of feeding

“…There are several possible explanations for the differences in call types we observed. For instance, previous studies by Brady et al (2021, 2022) suggest that the hill‐shaped call is a stereotypical call type produced by younger manatee calves. It's possible that one of the calves in our study only produced high squeaks while the older calf only produced squeaks.…”

“…Therefore, manatees could alter the structure of vocalizations in anticipation of feeding events. Additionally, the calls of Florida and Antillean manatee calves are distinctly structured and become more like adult calls over time suggesting the vocal behavior of calves is flexible (Brady et al, 2022).…”

Vocalizations of wild West Indian manatee vary across subspecies and geographic location

“…( 1234567890 www.nature.com/scientificreports/ higher than the calls reported from Puerto Rico. High squeaks are produced by both Antillean and Florida manatee calves, while adults produce squeaks 37,45,46 . This study indicates differences in acoustic parameters between adults (squeaks) and calves (high squeaks) between geographic locations.…”

“…Squeaks, high squeaks and squeals are more commonly observed in reports of Florida manatee communication 37 , 40 , 45 . Recent studies found the high squeak is a stereotypical call produced by both Florida 45 , 46 and Antillean calves 46 . As the animal grows, the hill-shaped contour of the high squeak appears to flatten and become a more linear call 46 .…”

“…Recent studies found the high squeak is a stereotypical call produced by both Florida 45 , 46 and Antillean calves 46 . As the animal grows, the hill-shaped contour of the high squeak appears to flatten and become a more linear call 46 . In addition, results showed few differences between calls produced between captive Florida and Antillean calves 46 .…”