title: Sound variation and function in captive Commerson's dolphins (Cephalorhynchus commersonii).
abstract: Commerson's dolphin (Cephalorhynchus commersonii), one of the smallest dolphin species, has been reported to produce only narrow-band high-frequency (NBHF) clicks and no whistles. To clarify their sound repertoire and examine the function of each type, we analysed the sounds and behaviour of captive Commerson's dolphins in Toba Aquarium, Japan. All recorded sounds were NBHF clicks with peak frequency >110kHz. The recorded click-trains were categorised into four types based on the changing pattern of their Inter-click intervals (ICI): Decreasing type, with continuously decreasing ICI during the last part of the train; Increasing type, with continuously increasing ICI during the last part; Fluctuating type, with fluctuating ICI; and Burst-pulse type, with very short and constant ICI. The frequency of the Decreasing type increased when approaching an object newly introduced to the tank, suggesting that the sound is used for echolocation on approach. The Burst-pulse type suddenly increased in front of the object and was often oriented towards it, suggesting that it was used for echolocation in close proximity to the object. In contrast, the Increasing type was rarely recorded during approach, but increased when a dolphin approached another dolphin. The Increasing and Burst-pulse types also increased when dolphins began social behaviours. These results suggest that some NBHF clicks have functions other than echolocation, such as communication.
authors.affiliation: Wildlife Research Center, Kyoto University, Tanaka-sekiden, Sakyo-ku, Kyoto 606-8203, Japan. Electronic address: marsh.greensdolphin@gmail.com.
authors.forename: Yayoi M
authors.initials: YM
authors.lastname: Yoshida
authors.affiliation: Wildlife Research Center, Kyoto University, Tanaka-sekiden, Sakyo-ku, Kyoto 606-8203, Japan; Institute of Innovative Science and Technology, Tokai University, 3-20-1, Orido, Shimizu-ku, Shizuoka 424-8610, Japan.
authors.forename: Tadamichi
authors.initials: T
authors.lastname: Morisaka
authors.affiliation: Institute of Innovative Science and Technology, Tokai University, 3-20-1, Orido, Shimizu-ku, Shizuoka 424-8610, Japan; JSPS, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Sakai
authors.affiliation: Tokyo Institute of Technology, W3-43 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Iwasaki
authors.affiliation: Toba Aquarium, 3-3-6, Toba-city, Mie 517-8517, Japan.
authors.forename: Ikuo
authors.initials: I
authors.lastname: Wakabayashi
authors.affiliation: Toba Aquarium, 3-3-6, Toba-city, Mie 517-8517, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Seko
authors.affiliation: Toba Aquarium, 3-3-6, Toba-city, Mie 517-8517, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Kasamatsu
authors.affiliation: National Research Institute of Fisheries Engineering, Hasaki, Ibaraki 314-0408, Japan; CREST, Japan Science and Technology Agency, Gobancho, Chiyoda-ku, Tokyo 102-0075, Japan.
authors.forename: Tomonari
authors.initials: T
authors.lastname: Akamatsu
authors.affiliation: Wildlife Research Center, Kyoto University, Tanaka-sekiden, Sakyo-ku, Kyoto 606-8203, Japan.
authors.forename: Shiro
authors.initials: S
authors.lastname: Kohshima
mesh_terms: D000819:Animal Communication; D000818:Animals; D004289:Dolphins / Q000502:physiology*; D004455:Echolocation / Q000502:physiology; D005260:Female; D008297:Male; D013016:Sound; D013037:Spatial Behavior / Q000502:physiology*; D014828:Vocalization, Animal / Q000502:physiology*
keywords: Acoustic behaviour; Captive; Clicks; Commerson's dolphin