Vocalizations of Amazon River Dolphins, Inia geoffrensis: Insights into the Evolutionary Origins of Delphinid Whistles

• Published in: Ethology Vol. 108; no. 7; pp. 601 - 612
• Main Authors: Podos, Jeffrey, Da Silva, Vera M. F., Rossi-Santos, Marcos R.
• Format: Journal Article
• Language: English
• Published: Berlin, Germany Blackwell Verlag GmbH 01.07.2002; Blackwell
• Subjects: Animal ethology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Mammalia; Psychology. Psychoanalysis. Psychiatry; Vertebrata; South America; America; Amazon Basin; Freshwater environment; Vocal repertoire; Animal communication; Vertebrata; Mammalia; Sound production; Taxonomy; Biological evolution; Interspecific comparison; Body size; Group size; Field study
• ISSN: 0179-1613; 1439-0310
• DOI: 10.1046/j.1439-0310.2002.00800.x

Oceanic dolphins (Odontoceti: Delphinidae) produce tonal whistles, the structure and function of which have been fairly well characterized. Less is known about the evolutionary origins of delphinid whistles, including basic information about vocal structure in sister taxa such as the Platanistidae river dolphins. Here we characterize vocalizations of the Amazon River dolphin (Inia geoffrensis), for which whistles have been reported but not well documented. We studied Inia at the Mamirauá Sustainable Development Reserve in central Brazilian Amazônia. During 480 5‐min blocks (over 5 weeks) we monitored and recorded vocalizations, noted group size and activity, and tallied frequencies of breathing and pre‐diving surfaces. Overall, Inia vocal output correlated positively with pre‐diving surfaces, suggesting that vocalizations are associated with feeding. Acoustic analyses revealed Inia vocalizations to be structurally distinct from typical delphinid whistles, including those of the delphinid Sotalia fluviatilis recorded at our field site. These data support the hypothesis that whistles are a recently derived vocalization unique to the Delphinidae.