Sirenians have dichromatic colour vision and tactile hairs but have not developed underwater echolocation. Amazonian manatees (Trichechus inunguis) live in turbid water and it has been unclear how they understand their surroundings. In this study, we recorded the 3D movements of two captive-raised Amazonian manatees. The results revealed that the manatees always swam in a circular pattern. Both animals used slower, narrower turning motions as they approached the flooded forests, which is abundant in aquatic vegetation. Therefore, we suggest that these two manatees swam in a circular pattern to detect all directions of their surroundings especially using sensitive facial bristles.
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We thank INPA staff and students, Shinichi Watanabe, Katsufumi Sato and Ichiro Aoki for their discussions and comments. This work was funded by the program “Bio-logging Science of the University of Tokyo (UTBLS)” led by N. Miyazaki and Sasagawa Scientific Research Grant, Japan Science Society, 2009.
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Kikuchi, M., da Silva, V.M.F., Rosas, F.C.W. et al. The implications of turning behaviour performed by Amazonian manatees after release into the wild. J Ethol 30, 187–190 (2012). https://doi.org/10.1007/s10164-011-0290-0
- Diving behaviour
- Trichechus inunguis