The Development of Bottlenose Dolphin Sonar System During the First Months of Life, the Role of the Mother and the Acoustic Interactions with the other Community Members

The birth of a dolphin in captivity is a rare occasion to study the learning and the development process of the sophisticated sonar system that these marine mammals use. In order to investigate the development of bottlenose dolphin sonar system during the first months of life, the role of the mother in the learning process and the acoustic interactions with other community members, ISMAR carried out a study on five calves (three females and two males) in three different pools from 1997 to 2005. The aims of the study were to point out: a) the time necessary for a calf to learn the use of biosonar, b) the role played by the mother and the other community members in this learning process, and c) the possible acoustical changes of the community in response to the entry of a new calf. Our observations indicate dolphin calves' inability to emit high frequency sounds during their first month of life. The five studied calves preferred to use low frequency pulses with a predominant peak around 50 kHz, unlike the other adult dolphins, that generally presented a more marked peak around 100 kHz. As known, low frequencies allow only a rough perception of the external world, while high frequencies make an extremely detailed analysis. The new born calves were acoustically influenced first by the mother and then by the father and the other juveniles of the group. At the same manner, all members of all the communities seemed to dynamically participate in the calves' learning phase and their acoustic behaviour was affected by the presence of the new entries. After some months the calves played a central role within the communities and the other members tended to modify the acoustic features of their biosonar adapting it to that of the calves.