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An Acoustic Play-Fight Signal in Bottlenose Dolphins (Tursiops truncatus) in Human Care
Abstract: Play-fighting is common in many mammals, especially among juveniles and subadults, providing a safe opportunity to practice behaviours important in adult life. To prevent escalation into a potentially dangerous real fight, play-fighting often is accompanied by acoustic and/or visual appeasement behaviours. We studied aggressive and play-fight behaviours in bottlenose dolphins (Tursiops truncatus) at the Kolmården Djurpark. The results showed that play-fighting subadult dolphins emitted a characteristic sound, which was never observed in aggressive interactions. This was a short pulse burst followed by an FM-whistle. By plotting pulse repetition rate (PRR) vs. duration of the bursts, two main clusters were found. The bottom cluster had a mean PRR of 59 pulses per second (pps), and a mean duration of 154 msec. The top cluster had a mean PRR of 502 pps and a mean duration of 149 msec. These play-fight clusters were compared separately to corresponding adult aggressive pulse burst clusters. Taking both PRR and duration into consideration, no significant difference was found between the top clusters, or between the bottom clusters, in the two age groups. The trailing whistles were divided into five different frequency contour categories. These did not resemble the signature whistles of any of the play-fighting dolphins. The average start and end frequencies were 13.0 kHz and 10.1 kHz, respectively, and the maximum and minimum frequencies were 13.7 kHz and 7.0 kHz, respectively. The mean duration was 410 msec. Based on the fact that this sound occurred only in play-fights, we propose that it helps prevent a play-fight from escalating into a real fight and, hence, is analogous to the “laugh” and “chuckle” seen in apes.
Key Words: BOTTLENOSE DOLPHIN; TURSIOPS TRUNCATUS; PLAY-FIGHT; ACOUSTIC APPEASEMENT SIGNAL; PULSE BURST; WHISTLE; KOLMARDENS DJURPARK
Document Type: Research article
Page Numbers: 187 – 194