Javan langur responses to the repeated exposure of ground survey and novel stimulus, unmanned aerial vehicles

Abstract

The use of small Unmanned Aerial Vehicles (UAVs; a.k.a “drones”) for ecological monitoring, conservation campaign, and management is increasing enormously. UAVs operate at low altitudes (<150 m) and in any terrain; thus, they are susceptible to interact with local fauna, generating a new type of anthropogenic disturbance that has not been systematically evaluated. Both policy-makers and practitioners require data about the potential impacts of UAVs on natural biota, but few studies exist. The research aims to compare behavioral responses from ground-based surveys vs. UAVs flights. Moreover, we conducted two experiments of UAVs overflights, specifically aiming to assess the responses of Trachypithecus auratus. Between January and March 2021, we conducted 24 UAVs flight approaches and 12 ground surveys at Mount Halimun-Salak National Park, Indonesia. We applied generalized linear mixed-effects models and Kruskal-Wallis tests to 364 behavioral scores obtained from two independent observers. When directly compared, the detection time was higher using UAVs (χ2 = 38.50; df= 1; p < 0.050), and behavioral responses by Javan langur to UAVs overflights at > 30 m were different from responses to ground surveys were more intense. Finally, we suggest data-driven best practices for UAVs use and the design of future UAVs-wildlife response studies.