Drone surveys of birds foraging in intertidal habitats: a proof-of-concept in Moreton Bay, Australia

Migratory shorebird populations are declining primarily because of intertidal habitat loss. Conservation efforts rely on monitoring, but ground surveys are generally impractical on extensive mudflats where shorebirds forage. On the 12th of March 2024, we used a DJI Mavic 3 Enterprise to conduct a proof-of-concept drone survey of shorebirds foraging on a 650 m × 250 m section of intertidal mudflat within Moreton Bay, Australia (GPS: −27.51, 153.41). We surveyed seven 16 m wide transects, spaced 75 m apart, across the mudflat perpendicular to the tidal front. We generated image mosaics for each transect and used manual and computer vision methods to locate and identify the birds. We also conducted concurrent ground counts and monitored for disturbance. Drone surveys detected 77 waterbirds, while ground counts recorded 46 birds, including 31 waterbirds, 2 seabirds, 12 non-migratory shorebirds, and 1 migratory shorebird. Differences in counts were attributed to excessive spacing between transects. We recommend that surveys: (1) use sensors capable of 0.5 cm pix−1 resolution and a large image footprint from above the flight initiation distance of sensitive species; (2) use multiple batteries and drones if needed; (3) use a transect-based flight path oriented perpendicular to the tidal front with transects spaced using conservative abundance estimates; (4) acquire approval to fly beyond visual line of sight and above 120 m if necessary; (5) ensure compatibility between flight application, camera, and flight plan; (6) consider processing images individually rather than as orthomosaics; (7) use computer vision tools for large sites or aggregations.