Analysis of whistles produced by the Tucuxi Dolphin Sotalia fluviatilis from Sepetiba Bay, Brazil

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Abstract

From July 2001 to June 2002, we recorded a total of 2h55min of Tucuxi Dolphin Sotalia fluviatilis vocalizations from Sepetiba Bay, Brazil (22º35'S-44º03'W). A total of 3350 whistles were analyzed quantitative and qualitatively and were divided into 124 types, by visual inspection of sonograms. The following parameters were measured: Initial Frequency, Final Frequency, Minimum Frequency, Maximum Frequency, Duration, Number of Inflections, Frequency at the Inflection Points, Frequency at 1/2, 1/4, and 3/4 of whistle duration, Presence of Frequency Modulation and Harmonics. Ascending type whistles (N=2719) were most common, representing 82% of the total. Dolphin behavior and average group size observed during recording influenced the whistle's quantitative and qualitative parameters. The results demonstrate the great diversity of whistles emitted and indicate a functional role of these vocalizations during the observed behaviors.

Translated abstract

De julho de 2001 até junho de 2002, foram gravados um total de 2h55min de vocalizações do Golfinho-Tucuxi Sotalia fluviatilis da Baía de Sepetiba, Brasil (22º35'S-44º03'W). Um total de 3350 assobios foram analisados quantitativa e qualitativamente e foram divididos em 124 tipos, pelo aspecto visual nos sonogramas. Os seguintes parâmetros foram medidos: Freqüência Inicial, Freqüência Final, Freqüência Mínima, Freqüência Máxima, Duração, Número de Inflecções, Freqüência nos Pontos de Inflecção, Freqüência a 1/2, 1/4, e 3/4 da duração do assobio, Presença de Modulação da Freqüência e Harmônicos. O tipo de assobio Ascendente (N=2719) foi o mais comum, representando 82% do total. O comportamento dos golfinhos e a média do tamanho do grupo observado durante as gravações influenciaram os parâmetros de freqüência dos assobios quantitativa e qualitativamente. Os resultados demonstram grande diversidade dos assobios emitidos e indicam papel funcional destas vocalizações durante os comportamentos.

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Most cited references 24

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ECOLOGY, BEHAVIOR AND SOCIAL ORGANIZATION OF THE BOTTLENOSE DOLPHIN: A REVIEW

Susan Shane, Bernd Würsig, Randall S Wells (1986)

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Context-specific use suggests that bottlenose dolphin signature whistles are cohesion calls.

VINCENT M JANIK, PETER J.B SLATER (1998)

Studies on captive bottlenose dolphins, Tursiops truncatus, have shown that each individual produces a stereotyped, individually specific signature whistle; however, no study has demonstrated clear context-dependent usage of these whistles. Thus, the hypothesis that signature whistles are used to maintain group cohesion remains untested. To investigate whether signature whistles are used only in contexts that would require a mechanism to maintain group cohesion, we examined whistle type usage in a group of four captive bottlenose dolphins in two contexts. Individuals were recorded while they were separate from the group and while they all swam in the same pool. Separations occurred spontaneously when one animal swam into another pool. No partitions were used and no aggressive interactions between dolphins preceded separations. Calling animals were identified by an amplitude comparison of the same sound recorded in the two pools. Each dolphin primarily produced one stereotyped signature whistle when it was separated from the group. Similarly the remaining group in the other pool also used primarily their signature whistles if one animal was in a separate pool. If all animals swam in the same pool almost only nonsignature whistles were used. Signature whistle copying was rare and did not initiate reunions or specific vocal responses. The results strongly support the hypothesis that signature whistles are used to maintain group cohesion. Copyright 1998 The Association for the Study of Animal Behaviour.