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Vocal behaviours of dolphins in the context of passing physical barriers [abstract]

E. Fritsch, H. Hultsch & D. Todt (1996). Vocal behaviours of dolphins in the context of passing physical barriers [abstract]. Bioacoustics, Volume 6 (4): 314 -315



Currently, there is a lively public discussion about the pros and cons of keeping dolphins in captivity, and a growing number of people demand the rehabilitation of these creatures. However, such an enterprise is difficult to achieve if one wants to do it in a biologically adequate manner. A few months ago we started to tackle this matter by studying a group of bottlenose dolphins (for details see Todt & Hultsch, 1995, Europ. Res. Cetaceans, 9). The Tursiops truncatus group is living in semi-free confinement adjacent to the Red Sea (site: Dolphin Reef/Eilat; size of site: > 10.000 m2, depth: 18 m; size of group: 5 adults (2/3), 3 juveniles (2/1), 1 call). The site is separated from the open sea by a wide-mesh net only, and has been recently a gate to the sea is open for two hours per day. For a long time, however, and otherwise than expected, only one individual made use of the opportunity to swim out for an excursion, whereas the other ones repeatedly inspected the gate without passing through completely. In order to further investigate why the dolphins seemed to have problems with such physical barriers, we built a new enclosure and invited the animals to explore and also to use it by voluntarily passing a second experimental gate. Then, we recorded how the dolphins coped with this setting (recording equipment linked to videocameras and hydrophones). Behavioural data were evaluated in terms of correlations between the vocalizations and stress-causing events, such as problems preceding or following any trial to pass the gate (for details of parametric analysis see Janik, Dehnhardt, Todt, 1994, Behav. Ecol. Sociobiol., 23, 15-21, or Hammerschmidt & Todt, 1995, Behaviour, 132, 381-399). Our results confirmed that bottlenose dolphins may indeed have problems in passing physical barriers. But they showed also how these animals finally solve such problems. In addition, the study documented a variety of vocalizations which were correlated to the quality of the particular test episodes or the animals' intrinsic state, respectively.