Monitoring the Hatching Success of Gulls Laridae and Terns Sternidae: A Comparison of Ground and Drone Methods

Abstract

Measuring the productivity of gulls Laridae and terns Sternidae is often difficult, due to natural obstacles of site access and the need to avoid disturbing nesting birds. Drones are increasingly being used for conservational and ecological applications and their use seems to overcome these problems, but data are still scarce on their use to assess breeding success. Our objective was to compare the effectiveness, time consumption, and safety for birds of drone-conducted monitoring of nest-specific hatching success with usual ground surveys of two species of gulls, including Slender-billed Gulls Chroicocephalus genei and Mediterranean Gulls Larus melanocephalus, and two species of terns, including Gull-billed Terns Gelochelidon nilotica and Sandwich Terns Thalasseus sandvicensis, breeding in the Adriatic wetlands of northeast Italy. We studied 400 nests (100 per species distributed in eight plots, each with 50 nests) and found no significant difference between the two methods in determining the number of eggs either laid or hatched per nest for all four focal species. The average coefficient of agreement between methods was high (kappa > 0.80 for all comparisons). The mean time spent determining the hatching success of 50 clutches with a drone (263 sec per plot) was significantly less than with ground surveys (760 sec per plot). There were no apparent negative effects of drone flights on nesting pairs, clutches, or young. Our results suggest that drones allow effective, rapid, and safe measurement of seabird breeding success in coastal areas.