How close can we get to seeing the private lives of fur seals and sea lions? Experimental UAV flights on the Southern Brazilian coast

Abstract

Recent advances in unmanned aerial vehicle (UAV) technology have made them a popular and accessible tool for wildlife research. Despite their popularity, there are some concerns about their potential negative impacts due to the possibility of causing disturbance to the species being monitored. We assessed the potential behavioral disturbance of low altitude UAVs on South American fur seals (Arctocephalus australis) and sea lions (Otaria flavescens) on a haulout site in southern Brazil (Wildlife Refuge of Ilha dos Lobos (WRIL)) between October 2022 and August 2023. Behavioral responses of each individual toward the UAV were classified (no response, vigilant or movement) and individuals were also classified according to their species. The probability of individuals expressing each one of the three behaviors at each altitude was assessed by Binomial and Multinomial Mixed Models. We flew a small UAV (DJI Air 2S) vertically above 731 South American sea lions, including 131 adult males, 590 subadult males and 10 juveniles; and 121 South American fur seals, including one subadult, one juvenile and 119 yearlings. For sea lions, vigilant and movement responses represented only 7.70% and 0.36% of behaviors observed during vertical approaches. South American fur seals appeared less perturbed by UAV presence, as only 1.56% of observed behaviors were classified as vigilant, and no movement responses were observed during vertical approaches. Similar results were found during horizontal flights over these species. The most frequent behavior observed in both species was no response, with a probability higher than 0.89 during vertical and horizontal approaches with drones, even at lower altitudes. Based on these results, we recommend that due to their benefits and minimal impact on the studied species, UAV monitoring studies of South American pinnipeds be conducted at a minimum altitude of 30 m at non-breeding sites, especially at haulout sites.