Abstract Observer bias and inexperience are challenging aspects of crocodile survey methods for determining population numbers and structure. Aerial surveys with either a helicopter or a fixed winged aircraft are generally preferred methods to ground surveys; however, the high cost of the former is a limiting factor. Recently unmanned aerial vehicles (UAVs) or drones have been proposed for surveys because of their potential of improving over traditional techniques of wildlife monitoring and as they have relatively lower costs. We investigated of the suitability of a UAV to determine numbers and structure of the Nile crocodile, Crocodylus niloticus, population during winter at Lake Nyamithi, Ndumo Game Reserve in South Africa. We used the UAV for eight flights covering ~132 ha. We also conducted a diurnal ground survey of crocodiles for comparison. Using the UAV, 287 crocodiles were identified and body length measured accurately for size class allocation whereas only 211 crocodiles were counted in the diurnal ground survey. Consequently, the UAV aerial survey recorded 26% more crocodiles. The potential of using UAVs to estimate crocodile population size and measure the total length (TL) of individuals accurately and precisely at a relatively low cost should improve management actions, enable monitoring of the crocodile populations annually and importantly avoid observer bias. Implications of this may facilitate improved crocodilian survey techniques.

中文翻译：

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使用无人驾驶飞行器（无人机）调查尼罗河鳄鱼种群：南非 Ndumo 禁猎区 Nyamithi 湖的案例研究

摘要 观察者偏见和缺乏经验是确定种群数量和结构的鳄鱼调查方法的挑战方面。使用直升机或固定翼飞机进行空中勘测通常是地面勘测的首选方法；然而，前者的高成本是一个限制因素。最近有人提议使用无人驾驶飞行器 (UAV) 或无人机进行调查，因为它们比传统的野生动物监测技术有改进的潜力，而且成本相对较低。我们调查了 UAV 的适用性，以确定冬季在南非 Ndumo 禁猎区 Nyamithi 湖的尼罗河鳄鱼（Crocodylus niloticus）种群的数量和结构。我们使用无人机进行了八次飞行，覆盖约 132 公顷。我们还对鳄鱼进行了昼夜调查以进行比较。使用无人机识别出 287 条鳄鱼并准确测量了体长以进行体型分配，而在昼夜地面调查中仅统计了 211 条鳄鱼。因此，无人机航测记录的鳄鱼数量增加了 26%。使用无人机估计鳄鱼种群大小并以相对较低的成本准确而精确地测量个体总长度 (TL) 的潜力应该会改善管理行动，能够每年监测鳄鱼种群，重要的是避免观察者偏见。这可能有助于改进鳄鱼调查技术。使用无人机估计鳄鱼种群大小并以相对较低的成本准确而精确地测量个体总长度 (TL) 的潜力应该会改善管理行动，能够每年监测鳄鱼种群，重要的是避免观察者偏见。这可能有助于改进鳄鱼调查技术。使用无人机估计鳄鱼种群大小并以相对较低的成本准确而精确地测量个体总长度 (TL) 的潜力应该会改善管理行动，能够每年监测鳄鱼种群，重要的是避免观察者偏见。这可能有助于改进鳄鱼调查技术。