Determining Nest Site Selection by Hawksbill Sea Turtles in the Persian Gulf Using Unmanned Aerial Vehicles

Abstract. Nest site selection is an important aspect of reproductive behavior in sea turtles, and it is influenced by biotic and abiotic beach characteristics. To date, the association between nesting beach characteristics and nest site selection has been explored manually at small scales; yet, hawksbill turtles (Eretmochelys imbricata) nest on a variety of beaches, with knowledge remaining limited on preferred habitat. Here, unmanned aerial vehicles were used to assess all available beaches, identify common characteristics, and determine the preferred nesting sites for hawksbill turtles in the Persian Gulf. High resolution photographs were taken of 236 nests with unmanned aerial vehicles on 7 main islands supporting 10 nesting beaches. The physical characteristics of these nests were photographed (e.g., elevation, slope, vegetation cover, and nest distance from vegetation and the high tide line). Slope was the most important factor regulating nesting activity. Most turtles nested on shallow-sloped beaches with 5° slopes or less (61.4%), at a distance of ≤ 15 m from the high tide line (71.8%), and generally ranged from 1 to 3 m (83.9%) above sea level. Most nests (87.7%) were laid close to the vegetation line (≤ 5 m) in sandy zones. Although there was high geomorphological diversity in landform among the islands, nesting habitat characteristics of hawksbills were consistent. Unmanned aerial vehicles provide a useful approach for identifying the nesting habitat preferences of sea turtles in a time- and cost-efficient manner, covering more surface while minimally disturbing fragile habitat.