Bibliography and Index of the Sirenia and Desmostylia  

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"Ichikawa, Kotaro"

Ichikawa, Kotaro; Akamatsu, Tomonari; Shinke, Tomio; Adulyanukosol, Kanjana; Arai, Nobuaki (detail)
Callback response of dugongs to conspecific chirp playbacks.
Journal of the Acoustical Society of America 129(6): 3623-3629. DOI: 10.1121/1.3586791. June 2011.
–ABSTRACT: Dugongs (Dugong dugon) produce bird-like calls such as chirps and trills. The vocal responses of dugongs to playbacks of several acoustic stimuli were investigated. Animals were exposed to four different playback stimuli: a recorded chirp from a wild dugong, a synthesized down-sweep sound, a synthesized constant-frequency sound, and silence. Wild dugongs vocalized more frequently after playback of broadcast chirps than after constant-frequency sounds or silence. The down-sweep sound also elicited more vocal responses than did silence. No significant difference was found between the broadcast chirps and the down-sweep sound. The ratio of wild dugong chirps to all calls and the dominant frequencies of the wild dugong calls were significantly higher during playbacks of broadcast chirps, down-sweep sounds, and constant-frequency sounds than during those of silence. The source level and duration of dugong chirps increased significantly as signaling distance increased. No significant correlation was found between signaling distance and the source level of trills. These results show that dugongs vocalize to playbacks of frequency-modulated signals and suggest that the source level of dugong chirps may be manipulated to compensate for transmission loss between the source and receiver. This study provides the first behavioral observations revealing the function of dugong chirps.
Ando-Mizobata, Noriko; Ichikawa, Kotaro; Arai, Nobuaki; Kato, Hidehiro (detail)
Does boat noise affect dugong (Dugong dugon) vocalization?
Mammal Study 39(2): 121-127. 1 tab. 2 figs. DOI: Mar. 23, 2014.
Matsuo, Yuuki; Ichikawa, Kotaro; Kinoshita, Kodzue; Arai, Nobuaki (detail)
Measurement of fecal progesterone in female dugong (Dugong dugon).
Proc. Design Symposium on Conservation of Ecosystem (The 13th SEASTAR2000 workshop) 2: 55-58. 1 tab. 2 figs. March 2014.
–ABSTRACT: In this study, we investigate the possibility of measuring fecal progesterone (P4) of dugongs in captivity. Fecal samples were collected from a captive adult female dugong kept at Toba aquarium in November 2012 and February 2013, and fecal P4 of these samples was measured using enzyme immunoassay (EIA). To establish a measuring system, we compared the results of measurements applying different dilution rates of primary antibody and enzyme linked antigen, and decided the best experimental condition for accurate measurement. We then measured P4 concentrations of the dugong's fecal samples. Significant difference in the P4 concentrations was not found among the samples collected in November and February. Thus it is suggested the dugong was not in estrous period when the samples were collected. We succeeded in extracting and measuring fecal P4 of the dugong, and for further study, we plan to apply this method to monitoring of estrous cycle of dugongs.

Daryl P. Domning, Research Associate, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, and Laboratory of Evolutionary Biology, Department of Anatomy, College of Medicine, Howard University, Washington, D.C. 20059.
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