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Whistle Stability and Variation in Captive Bottlenose Dolphins (Tursiops truncatus) Recorded in Isolation and Social Contexts
Abstract: Common bottlenose dolphins (Tursiops truncatus) produce a range of underwater vocalizations, both pulsed (echolocation clicks and burst-pulses) and nonpulsed (whistles). Whistles may be emitted in stereotyped (signature) or variant patterns, and their production might be affected by sex, age, environmental, and social contexts. This study examined, non-intrusively, the whistle emissions of six captive bottlenose dolphins at Zoomarine in Algarve, Portugal, in two separate time sets and three different contexts: two of the animals in isolation in 2008, and all six in 2012, both segregated from their group and in social context. From a total of 1,681 whistles, 1,249 were analyzed from 32 samples in different contexts: seven samples in isolation in 2008, 18 in segregation in 2012, and seven in social context. Through visual inspection of spectrograms, whistles were classified into 12 different contour categories. Only one category was found in both time sets and could be considered a signature whistle by SIGID criteria (Janik et al., 2013). This contour was associated with the same animal in 2008 and 2012. Whistle emission rates were 7.8 times higher in isolation as compared with social context, and significant differences were also found in the end and maximum frequencies as well as number of inflections and loops. Multiloop whistles were more common in isolation than in social contexts. The variant (nonstereotyped) contours dominated the whistle production in segregated contexts (but not by isolated animals) as well as in social contexts. This study highlights the importance of examining the nonstereotyped portion of the bottlenose dolphin’s whistle repertoire in different contexts as signature whistle production may not be a constant or universal phenomenon.
Key Words: common bottlenose dolphins, Tursiops truncatus, whistles, emission rates, isolation, social contexts, captivity
Document Type: Research Article
Page Numbers: 1-13