VOCAL PRODUCTION BY FREE-RANGING BOTTLENOSE DOLPHIN MOTHER INFANT PAIRS DURING FEEDING ACTIVITIES

Common bottlenose dolphins (Tursiops truncatus) produce different acoustic emissions, including a diverse repertoire of both tonal and burst pulsed sounds used for communicative purposes. In this study we examine the vocal production of free-ranging bottlenose dolphin mother-infant pairs, during feeding activities, to gain insight into the functional significance of vocalizations. The study area (North-eastern coast of Sardinia, Italy) provides a unique opportunity to study vocal production of free-ranging bottlenose dolphins because on a year-round, daily basis, resident individuals tend to follow predictable spatial patterns foraging onshore. Results are based on focal observations and simultaneous recordings of resident females and their calves from 2007 to 2010. During 18 sightings with behavioural observations and simultaneous recordings of the mother-calf pairs alone, 102 tonal and 351 burst-pulsed sounds were detected. The acoustic repertoire observed in these pairs was extremely diverse, with a higher production rate of whistles and some types of burts-pulsed sounds. Whistle emission of mother-calf pairs was significantly higher than dyads formed exclusively by adults. The results of this study verify that tonal sounds (particularly whistles) play an important role in the communication between mother and calf. Past studies have suggested that the production of repeated whistles by bottlenose dolphins may indicate the use of stereotyped signature whistles. Thus, the use of tonal vocalizations as contact calls between mother and calf supports the individual recognition hypothesis. Highly individualized signature whistles may be particularly useful in mother-calf pairs in which mothers maintain consistent, long term associations with their calves.