Fluke-made bubble rings as toys in bottlenose dolphin calves (Tursiops truncatus)

Cetaceans display considerable patterns of bubble formation and manipulation for different purposes. While position and acoustic functions of bubbles have been extensively discussed, few details are known about their use in playing behaviour. The aim of the present work was to conduct a systematic observational study on a novel pattern of flukemade bubble rings (FBR) and associated play behaviour in two captive calves of Tursiops truncatus. The birth of two, half-siblings bottlenose dolphins less than one month apart in the same aquarium presented a good opportunity to address the issue of individual differences and possible mimicry of such behaviour. Focal animal sampling (Altmann, 1974) sessions lasting 15 min were carried out for each calf according to a decreasing temporal schedule. The following parameters were scored and obtained for each calf: (a) mean frequency of FBR per session, (b) FBR by time of day, and (c) frequency of FBR associated play behaviour per session. FBR formation appeared to be, for both animals, a two-phase action producing a loud percussive sound. A trend in the mean frequency of FBR suggests a possible seasonal negative relationship with human activities. Moreover, the two calves usually were seen together and mimicked each other during FBR formation. Finally, 7 different behavioural categories were observed after FBR formation and their sequence appeared to be well defined. In conclusion, this paper describes a novel form of play in two bottlenose dolphin calves. Even though data are limited by a small sample size and are only suggestive, they do indicate that FBR formation and the calves’ ability to manipulate bubble rings could reflect the learning flexibility of the young dolphins and implies a high behavioural versatility.