Monitoring the population size of threatened primate species with minimal disturbance is becoming an outstanding requirement for conservation and wildlife management. Drones with thermal infrared (TIR) and visible spectrum (RGB) imaging are increasingly used to survey arboreal primates, but ground-truthing is still required to assess the effectiveness of drone-based count estimates. Our pilot study aims to assess the ability of a drone with both TIR and RGB sensors to detect, count, and identify semi-wild population of four endangered species of langurs and gibbon in the Endangered Primate Rescue Center (EPRC) in northern Vietnam. We found that TIR imagery enabled higher detection rates compared to RGB imagery and obtained an accurate count with the TIR only after four drone flights. We could identify langurs species based on thermal signature at a flight height of 50 m from the ground level (max tree height = 15 m), via size and shape of the body. With TIR imagery, we were able to record inconspicuous behaviors such as foraging and play. While some individuals initially showed flight or avoidance behaviors when the drone was sighted, these behaviors decreased or were absent on following drone surveys. Our study suggests that monitoring and precisely counting langur and gibbon species populations could be successful with the use of thermal drones only.

在最小干扰的情况下监测受威胁灵长类动物的种群规模正在成为保护和野生动物管理的突出要求。具有热红外（TIR）和可见光谱（RGB）成像功能的无人机越来越多地用于调查树栖灵长类动物，但仍需要地面实况来评估基于无人机的计数估计的有效性。我们的试点研究旨在评估配备 TIR 和 RGB 传感器的无人机检测、计数和识别越南北部濒危灵长类动物救援中心 (EPRC) 四种濒危叶猴和长臂猿半野生种群的能力。我们发现，与 RGB 图像相比，TIR 图像的检测率更高，并且仅在四次无人机飞行后才通过 TIR 获得了准确的计数。我们可以根据距地面 50 m 飞行高度（最大树高 = 15 m）的热特征，通过身体的大小和形状来识别叶猴的物种。借助 TIR 图像，我们能够记录觅食和玩耍等不显眼的行为。虽然有些人在看到无人机时最初表现出飞行或回避行为，但在随后的无人机调查中，这些行为减少或消失。我们的研究表明，仅使用热感无人机就可以成功监测和精确计数叶猴和长臂猿物种数量。虽然有些人在看到无人机时最初表现出飞行或回避行为，但在随后的无人机调查中，这些行为减少或消失。我们的研究表明，仅使用热感无人机就可以成功监测和精确计数叶猴和长臂猿物种数量。虽然有些人在看到无人机时最初表现出飞行或回避行为，但在随后的无人机调查中，这些行为减少或消失。我们的研究表明，仅使用热感无人机就可以成功监测和精确计数叶猴和长臂猿物种数量。