Estimates of dolphin group structure and behaviour differ between drone and boat observations

Monitoring animal behaviour is vital for ecology and conservation, yet surface-level observations can influence estimates of group size and activity budgets because of their limited lateral perspective. Using Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) in Coffin Bay, South Australia, we examined how estimates of group structure and behaviour differ between drone and boat-based observations. We further assessed how group characteristics, environmental conditions, and flight height influenced platform differences and behavioural budgets. We collected concurrent drone and boat-based observations across 63 dolphin sightings (October 2023–July 2024) and analysed agreement and drivers of platform differences using regression and multinomial modelling. Discrepancies in group size increased with group size, with boat-based observations recording smaller group size estimates than drone observations; differences rose by ~ 7.8% per additional adult and were ~ 2.6-fold greater in groups with spread cohesion (5–10 m). Agreement in age composition declined by ~ 10% per additional individual but increased when calves were present and during travelling. Behavioural agreement was lowest for milling and travelling, indicating systematic differences in classifications between platforms. Behavioural budgets differed between platforms, with boat observations recording a greater proportion of socialising. Drone flight height had no detectable effects on behavioural budgets, whereas sea surface temperature (SST) positively predicted drone-recorded travelling. These findings demonstrate that observation perspective systematically shapes behavioural inference and highlights drones as a complementary tool for quantifying for platform-specific differences in mobile, social taxa.