Studies on captive bottlenosed dolphins Tursiops truncatus us have shown that they produce individually specific calls named signature whistles and that these whistles are sometimes imitated by other group members. It has been hyphothesised that signature whistles play an important role in individual recognition and that bottlenosed dolphins use imitation of signature whistles to initiate social interaction with specific group members. However, information on the individual, context-related usage of vocalizations in wild dolphins is still scarce, mainly because of the inaccessibility of the marine environment and the lack of observable correlates to sound production in these animals. In this study a hydrophone array was employed in a 500 m wide, natural channel to investigate the vocal behaviour of free-ranging bottlenosed dolphins in relation to spatial distance between individuals and their surface activities. The position of a vocalizing animal was calculated by comparing differences in times of arrival of the sound at different hydrophones of the array. Video recordings from the shore provided additional information on surface behaviour and position of all the animals present. First results showed that whistle interactions with non- matching whistle types as well as signature whistle imitation, occur frequently between individuals in the wild. This project was funded by a DAAD-Doktorandenstipendium aus Mitteln des zweiten Hochschulsbnderprogramms.