@article{oai:nagasaki-u.repo.nii.ac.jp:00008051,
 author = {Nakasai, Kei and Takemura, Akira},
 journal = {長崎大学水産学部研究報告, Bulletin of the Faculty of Fisheries, Nagasaki University},
 month = {Dec},
 note = {The investigation on the underwater calls of three kinds of river dolphins, i.e., Amazon Dolphin (Inia geoffrensis), Buffeo negro (Sotalia fluviatilis) and La Plata river dolphin (Pontopolia blainvillei) that live in waters in South America was carried out. It has been considered that these dolphins made better use of the underwater calls than any other sea dolphins on account of their circumstances. However, conversely it was made clear that the underwater calls were lacking of the variety and frequencies, and moreover they were different in character from the underwater calls of the Ganges river dolphin (Platanista gangetica). For example, Buffeo negro did not emit the stratiformed sound, and both whistle and clicks of Amazon dolphin were limited in the range of low frequency. And also the frequency in their use of calls was exceedingly low. The underwater calls of La Plata river dolphin could not be recorded though the opportunity of observation was little.!?1. The underwater calls of the river dolphins in South America (Buffeo negro and Amazon dolphin) were recorded in natural environment and analys ed in comparison with the sea dolphin and the Ganges river dolphin. 2. Clear difference between the Buffeo negro and the Amazon river dolphin was obtained and further the underwater calls of these dolphins were different from that of the sea dolphins and the Ganges river dolphin. 3. For Buffeo negro, the stratiformed sound was not emitted. The frequency of whistle was higher than that of Amazon dolphin and clicks also showed the same tendency. 4. The frequency in use of calls was lower compared with any other kinds of dolphins., 長崎大学水産学部研究報告, v.40, pp.7-13; 1975},
 pages = {7--13},
 title = {Studies on the Underwater Sound―VI On the Underwater Calls of Fresh Water Dolphins in South America},
 volume = {40},
 year = {1975}
}