Sounds are particularly important for animals that live in complex social communities. In this study, we assessed the communication calls (whistles) that common bottlenose dolphins emit during their foraging activities in the absence and presence of motor boats and during dolphin depredation on trawlers, in Alghero (Sardinia, Italy) and Cres-Lošinj Archipelago (Croatia). The latter behaviour involves foraging on concentrated food sources during very noisy human activity and may require the emission of distinctive whistles. Thus, we investigated if whistle structure, in terms of frequency and time parameters, changes depending on these three foraging contexts. In Sardinia, during foraging in interaction with trawlers, whistles differed from those emitted during the other foraging contexts. Conversely, in Cres-Lošinj, significant variations in whistles were found to be related mainly to the presence of motor boats. This study represents the first report on how two dolphin populations adopt different acoustic tactics in the context of similar foraging behaviour. By investigating the effects of opportunistic foraging on acoustic repertoires, we provide new findings on the acoustic adaptation of dolphins to local conditions and contribute to understanding the relationships between dolphins and human activities, such as fishing and boat traffic.
Keywords: Acoustic communication; Behaviour; Boat presence; Bottom trawlers; Mediterranean Sea; Tursiops truncatus.
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