Possible occurrence of signature whistles in a population of Sotalia guianensis (Cetacea, Delphinidae) living in Sepetiba Bay, Brazil.

According to the "signature whistle" hypothesis, dolphins emit stereotypic sequential whistles whose function is to transmit the identity and location of the whistling animal. However, it has also been proposed that the information signature may be expressed by distinct acoustical features within a single type of whistle shared by a population of dolphins. In an attempt to detect signature whistles from Sotalia guianensis living in Sepetiba Bay, Rio de Janeiro, Brazil, 12 h of vocalizations were recorded. Following analysis of the spectrograms, the whistles were classified according to visual inspection and the contour similarity method. Although the identities of the whistling animals were not established, 202 whistle sequences were selected and classified by visual inspection into 27 different types of potential signature whistles. However, there was a large discrepancy between this classification method and that obtained using the quantitative contour similarity method. The arguments in support of the premise that S. guianensis produces signature whistles are discussed and the limitations of the classification systems employed are examined.