Circumventing Blind Angles and Disturbance: Evaluating UAS for Monitoring Cliff-Nesting Seabirds

Unoccupied Aerial Systems (UASs) offer great potential for monitoring breeding colonial seabirds. However, survey flights need to be planned carefully to maximize detection of birds, allow for reliable counts, and minimize disturbance. In this study, we evaluated UAS-based monitoring for the most numerous seabird species in the Faroe Islands, the northern fulmar (Fulmarus glacialis), assessing both disturbance and optimal viewing angles. We found that behavioral disturbance could be minimized by adhering to a set of strict operating protocols, including strategic and flexible flight paths that ensured UAS distances remained above vigilance thresholds, allowing for initial habituation and limiting responses to the presence of the UAS. During surveys, quantifiable behavioral alterations (vigilance) were observed at distances ≤57.5 m in mixed areas containing both incubating and resting individuals, and ≤32.9 m in areas with only incubating individuals. At greater distances, only light responses (head turning) occurred. To optimize monitoring efficiency, we found that a slight downward camera tilt of −13.8° consistently provided the highest bird visibility, detecting 93% of individuals. Complete visibility was achieved by covering a range from −30° to −1.3°, depending on terrain type and bird age group, highlighting the observation angle as a critical factor for reliable surveys in the investigated complex topography. Overall, these results will provide a strong foundation for further research into tailored flight and survey protocols for cliff-nesting seabirds utilizing UAS technology.