Variation of signature whistles related to the bottlenose dolphins group (Tursiops truncatus): the case of Losinj archipelago.

Bioacoustics is an important field of research particularly for cetaceans. Bottlenose dolphins (Tursiops truncatus) are a highly social species, and they use sound emissions to communicate with each other, to echolocate and to feed themselves. The study was conducted in the Cres-Lošinj archipelago, located in the north-eastern Adriatic Sea in Croatia. Data considered in this study were collected between May and September 2016, between June and September 2017 and between April and June 2025 with a RESON TC 4032 hydrophone. A total of 1426 whistles were analysed from 15 hours and 22 minutes of recordings. Furthermore, a photo-identification analysis was conducted on the animals present during the recordings using the natural marks on their dorsal fins, which were photographed with a digital camera. For each whistle, 15 parameters were analysed: duration, start frequency, end frequency, minimum frequency, maximum frequency, frequency range, initial slope, final slope, number of flexes, number of steps, presence of harmonics, number of peaks, number of troughs, presence of interruptions and the number of interruptions. An initial analysis was carried out on the characteristics of the whistles, also considering different factors, such as the presence of calves in the group and the number of boats present during the recording. Afterward, the same analysis was carried out on a sub-group of the total dataset to understand if these individuals caused a variation in the parameters. These dolphins were referred to by us as “charismatic”. The result of this study can be used to better understand the communication of the bottlenose dolphins in this area. Furthermore, the study could determine whether communication within a group differs if “charismatic” individuals are present, or if it remains the same, as these individuals have a great influence on the group. Future acoustic studies will help investigate sound emissions variations in bottlenose dolphin vocalization.