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Low-frequency sounds emitted by Sotalia fluviatilis guianensis(Cetacea: Delphinidae) in an estuarine region in southeastern Brazil

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Abstract:

Recordings of the vocalizations of the dolphin Sotalia fluviatilis guianensis were made in an estuarine complex at Cananéia in southeastern Brazil over a period of 10 years (1989–1998). This area is characterized by mangroves and the constant presence of dolphins. Recordings were obtained at depths of 2–4 m using digital and analog recorders at a speed of 19 cm/s. Four classes of sounds were identified. "Whistles," which are used in social activities, occurred with the greatest frequency (2 = 58.92, df = 3, P < 0.001). "Calls," which were very variable in form, were the second most common class used by family groups (2 = 10.96, df = 2, 0.005 > P >0.001). There were no differences in the rates at which schools emitted whistles and calls (2 = 2.12, df = 1, 0.25 > P >0.10). "Gargles" were apparently emitted by calves and were similar in structure to a low-frequency call. The fourth class, "clicks," are used in echolocation. Clicks varied considerably in their frequency of occurrence and frequency of emission, and were not always detected. There were significant differences in emission rates among the four classes (2 = 18.73, df = 3, P < 0.001). In addition, which class of sound was emitted depended on the type of activity exhibited by the dolphins (displacement, fishing, social) and on the social structure (family or school) adopted.

Les cris du dauphin Sotalia fluviatilis guianensis ont étéenregistrés dans un complexe estuarien à Cananéia dans le sud-est du Brésil au cours d'une période de 10 ans (1989–1998). Cette région est dominée par les mangroves et les dauphins y restent en permanence. Des enregistrements ont été obtenus àdes profondeurs de 2–4 m au moyen d'enregistreurs numériques et analogiques, à une vitesse de 19 cm/s. Nous reconnaissons quatre classes de cris. Les « sifflements », émis au cours d'activités sociales, sont les cris les plus fréquents (2 = 58,92, dl = 3, P < 0,001). Les « appels », de fréquences très variables, viennent en second; ce sont les cris utilisés par les groupes familiaux (2 = 10,96, dl = 2, 0,005 > P > 0,001). Il n'y a pas de différences d'un banc de dauphins à un autre quant aux taux d'émission des sifflements et des appels (2 = 2,12, dl = 1, 0,25 > P > 0,10). Les « gargouillis » semblent provenir des petits et sont de structure semblable à celle des appels de basse fréquence. Les cris de la quatrième classe, les « claquements », servent àl'écholocation. La fréquence d'utilisation des claquements et leur fréquence d'émission varient considérablement et ils ne sont pas toujours détectés. Nous avons trouvédes différences significatives entre les taux d'émission des quatre classes de cris (2 = 18,73, dl = 3, P <0,001). De plus, la classe de son utilisée dépend du type d'activitédes dauphins (déplacements, pêche, activités sociales) et de la structure sociale du groupe (famille ou banc) auquel ils appartiennent.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2001-01-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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