Effectiveness, efficiency, and safety of censusing eurasian oystercatchers haematopus ostralegus by unmanned aircraft

Abstract

Censusing oystercatcher Haematopus spp. can be difficult. Challenges often arise from difficulties with site access and the need to avoid disturbing nesting birds. Unmanned aerial systems are increasingly used in conservation and ecological research. The present study evaluated the effectiveness, managerial efficiency, and safety of the use of unmanned aerial vehicles (drones) to count Eurasian Oystercatchers Haematopus ostralegus breeding at the Po Delta in northeast Italy. Flights encountered 142 oystercatcher pairs, in contrast to the 135 pairs that were counted through traditional ground census. Combining the results from both methods, 140 breeding pairs of oystercatchers (110 confirmed, 30 probable) were located. The mean time required to census with the drone was far less than that required to census by ground (5.6 ± 5.7 min vs. 37 ± 38 min, respectively, for our study area). This corresponds to an expenditure of 3 708 € for ground census vs. 460 € for drone census, leading to a cost reduction of 88 %. No apparent negative effects on nesting pairs or clutches were observed. Our major findings were as follows: 1) compared with traditional ground census, using drones in waterbird counts saved time and money; 2) there was no significant difference in overall counts between drone and observer counts; and 3) despite their advantages, drones are associated with an increased disturbance response among Eurasian Oystercatchers—often leaving nests exposed and vulnerable to depredation—and this should be carefully considered when selecting a study approach.