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Sound Characteristics and Primary Descriptions of Vocalizations Associated with Behaviours of Captive Irrawaddy Dolphins (Orcaella brevirostris)
Abstract: Even though there have been several studies on vocal repertoires and behaviours of Irrawaddy dolphins (Orcaella brevirostris) in recent de-cades, important pieces of information are still missing, especially the sounds produced in captivity where environmental differences can affect their physical and acoustic behaviour. Over 40 h of observations in March and November 2014, with almost 7,000 vocalizations sampled, it was determined that the captive Irrawaddy dolphins produced various types of sound, including two types of clicks (n = 3,898), five types of pulsed sounds (n = 2,807), and nine types of whistles (n = 44). This work also describes three newly discovered pulsed sounds and all nine whistle types in this species. Clicks were observed most frequently during feeding and swimming in navigational contexts. Pulsed sounds were mainly used in social or emotional contexts associated with various behaviours, including aggression, sexual arousal, and tourist encounters. Whistles, on the other hand, were scarcely heard, which might imply that the communication was not necessary. Whistling behaviours were contradictory to those reported for other wild delphinids; this difference was potentially caused by habituation in captivity. Vocalizations, which increased concurrently with activity levels, were recorded at a significantly higher rate (p < 0.05) when tourists were present during swim-with-dolphin programs. This is the first study to correlate Irrawaddy dolphin sounds and behaviours in captivity and represents the first time that all three sound categories have been recorded for this species in captivity.
Key Words: cetacean, behaviour, acoustic, sound, Irrawaddy dolphin, Orcaella brevirostris, captivity, swim-with-dolphin program, vocalization
Document Type: Research Article
Page Numbers: 519-530