If the sheep goes baa, the duck goes quack and the cow goes moo, what about the manatee?  Manatee’s (genus Trichechus), nicknamed “the sea cow”, are large aquatic mammals with stouts and a flat rounded tail used to help them propel themselves through water. Their physical characteristics consist of flippers that lack nails which are used for water movement and food manipulation. There are three species of manatees which can range from blackish, brown, and a dullish gray color.

You can find the three species in tropical and subtropical Atlantic coast with inland waters of the Amazon and Niger rivers called the Amazonian manatee (T. inunguis) [1]. The West African manatee (T. senegalensis) are found in slow moving rivers around coastal areas in Senegal and Angola. The most commonly known type are Florida manatees (Trichechus manatus latirostris) are part of the West India manatee (T. manatus) [1]. Florida manatees can grow up to 13 feet and weigh more than 3,000 pounds while the Amazonian manatees are much smaller and grow up to 9 feet and weigh around 1,000 pounds [1].

The phenotypes of manatees have adapted for eating aquatic plants since their lips have specialized sensory bristles and hairs to distinguish between the food plants. Since these aquatic food plants are low in energy value and protein, manatees need to eat them in high proportions in order to maintain their size, however, manatees have very low metabolic rates which means they fast for long periods of time and survive on these low energy plants [1]. Researches have determined how they eat, but how do they communicate?

Similar to humans, manatees also have vocal folds which they use to create high pitch noises. The larynx and vocal folds in manatees create longer duration calls from an increase tension of the respiratory muscle. These large squishy gentle mammals don’t just make these noises for fun, these noises are used to communicate in a behavioral social setting. A marine mammologist at Mote Marine Laboratory and Aquarium in Florida, Beth Brady, began to research what these cries meant. Researchers recorded Florida manatees communicating in shallow water and began to decipher the high-pitched signals. The purpose of these the vocalizations is to convey all different meanings [2]. Manatees change pitch of the sound and the length of the sound for different distinguished meaning.

Brady and her team spent many years studying these manatee pitches to determine what each meant. They would use a hydrophone off the side of a kayak and paddle through fields of seagrass or freshwater rivers to listen and take notes of what the manatees were doing while communicating [2]. The data collected was analyzed into three categories; social play, stress, and mother and calf interactions. Social play sounded more of a squeak-squeals, stressed noises were higher and described as a squeak, and the highest squeak was made when communicating between a mother and her calf. The frequency was shown for each noise the manatees made: squeak-squeals were straight lines with space in between, high squeaks were curved lives stacked on top of each other, and squeals were smudged lines much closer together.

The data collected showed a relationship that high squeaks were produced when calves were present however, the production of high squeaks appeared not to associate with behavior rather to identify if a calf was present. The researches also concluded that squeak-squeals during social play were used for mating. The squeak-squeals were observed during resting and feeding which may indicated heighted arousal from finding a food source [3]. They were mostly observed when manatees were either feeding or resting with other animals nearby. They determined the squeak-squeals correlated with high arousal, but did not determine if the arousal stemmed from aggression or others. The manatees produced a specific squeak call only when they are stressed. This was determined by the motivation structure rules, which predict that animals that are in a state of fear will produce tonal calls [3].

Discovering these three basic calls can unlock the potential of understanding communication between manatees. These beautiful elegant mammals are more than just floating objects in water. Manatees are intelligent organisms and we are just beginning to discover how they communicate. So the next time you see a “sea cow”, remember they don’t say moo, they actual go squeal!

References:

[1] Encyclopædia Britannica, inc. (2023, September 27). Manatee. Encyclopædia Britannica. https://www.britannica.com/animal/manatee

[2] Papp, A. (2022, March 30). New research decodes the sea cow’s hidden language. Scientific American. https://www.scientificamerican.com/podcast/episode/new-research-decodes-the-sea-cows-hidden-language/

[3] Brady, B.,  Moore, J., &  Love, K. (2022).  Behavior related vocalizations of the Florida manatee (Trichechus manatus latirostris). Marine Mammal Science,  38(3),  975989. https://doi-org.libproxy.kenyon.edu/10.1111/mms.12904

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