<p>Signature vocalisations play a key role in individual identification in social animals, ensuring recognition in dynamic group contexts. Bottlenose dolphins are known for using individually distinctive whistles in societies exhibiting fission-fusion dynamics, yet their use across varying social and ecological contexts remains poorly understood. This study explores how wild bottlenose dolphins use signature whistles across different populations, behaviours, and group sizes, examining the contextual factors influencing their production. Acoustic recordings from long-term monitoring studies in the Mediterranean Sea (Sardinia) and Atlantic Ocean (Galicia) collected over 15 years were analysed. Signature whistle presence was noted in 1119 acoustic samples, and a generalised linear mixed model (GLMM) approach was employed to assess whether factors such as location, behaviour, group size and composition drive signature whistle production. Results indicate that signature whistle production is shaped by an interaction between group size and location. The probability of signature whistle presence increased with group size, with a steeper rise in areas where dolphins occur in smaller aggregations (Sardinia) than in areas where larger groups are formed (Galicia). This suggests that the presence of signature whistles depends on local social and ecological conditions, which act as drivers of group size variation and thereby influence communication patterns. Behavioural context also played a role, with higher probabilities of signature whistle production during social interactions compared to travelling, potentially to maintain contact during active group dynamics. These findings contribute to understanding the contextual presence of signature whistles and demonstrate how their production varies with social structure and environmental settings.</p>