Context: West African crocodylian populations are declining and in need of conservation action. Surveys and other monitoring methods are critical components of crocodile conservation programs; however, surveys are often hindered by logistical, financial and detectability constraints. Increasingly used in wildlife monitoring programs, drones can enhance monitoring and conservation efficacy.

Aims: This study aimed to determine a standard drone crocodylian survey protocol and evaluate the drones as a tool to survey the diverse crocodylian assemblage of West Africa.

Methods: We surveyed crocodile populations in Benin, Côte d’Ivoire, and Niger in 2017 and 2018, by using the DJI Phantom 4 Pro drone and via traditional diurnal and nocturnal spotlight surveys. We used a series of test flights to first evaluate the impact of drones on crocodylian behaviour and determine standard flight parameters that optimise detectability. We then, consecutively, implemented the three survey methods at 23 sites to compare the efficacy of drones against traditional crocodylian survey methods.

Key results: Crocodylus suchus can be closely approached (>10 m altitude) and consumer-grade drones do not elicit flight responses in West African large mammals and birds at altitudes of >40–60 m. Altitude and other flight parameters did not affect detectability, because high-resolution photos allowed accurate counting. Observer experience, field conditions (e.g. wind, sun reflection), and site characteristics (e.g. vegetation, homogeneity) all significantly affected detectability. Drone-based crocodylian surveys should be implemented from 40 m altitude in the first third of the day. Comparing survey methods, drones performed better than did traditional diurnal surveys but worse than standard nocturnal spotlight counts. The latter not only detected more individuals, but also a greater size-class diversity. However, drone surveys provide advantages over traditional methods, including precise size estimation, less disturbance, and the ability to cover greater and more remote areas. Drone survey photos allow for repeatable and quantifiable habitat assessments, detection of encroachment and other illegal activities, and leave a permanent record.

Conclusions: Overall, drones offer a valuable and cost-effective alternative for surveying crocodylian populations with compelling secondary benefits, although they may not be suitable in all cases and for all species.

Implications: We propose a standardised and optimised protocol for drone-based crocodylian surveys that could be used for sustainable conservation programs of crocodylians in West Africa and globally.

背景：西非鳄鱼种群正在下降，需要采取保护行动。调查和其他监测方法是鳄鱼保护计划的重要组成部分；然而，调查往往受到后勤、财政和可探测性限制的阻碍。无人机越来越多地用于野生动物监测计划，可以提高监测和保护效率。

目的：本研究旨在确定标准的无人机鳄鱼调查协议，并评估无人机作为调查西非多样化鳄鱼组合的工具。

方法：我们在 2017 年和 2018 年对贝宁、科特迪瓦和尼日尔的鳄鱼种群进行了调查，使用 DJI Phantom 4 Pro 无人机，并通过传统的白天和夜间聚光灯调查。我们使用一系列试飞来首先评估无人机对鳄鱼行为的影响，并确定优化可检测性的标准飞行参数。然后，我们连续在 23 个地点实施了三种调查方法，以比较无人机与传统鳄鱼调查方法的功效。

主要结果：鳄鱼可以近距离接近（> 10 m 高度），消费级无人机在> 40-60 m 的高度不会引起西非大型哺乳动物和鸟类的飞行反应。高度和其他飞行参数不影响可探测性，因为高分辨率照片允许准确计数。观察者的经验、现场条件（例如风、太阳反射）和场地特征（例如植被、同质性）都显着影响了可探测性。应在一天的前三分之一从 40 m 高度实施基于无人机的鳄鱼调查。比较调查方法，无人机比传统的昼夜调查表现更好，但比标准夜间聚光灯计数差。后者不仅检测到更多的个体，而且还检测到更大的体型多样性。然而，无人机勘测比传统方法具有优势，包括精确的尺寸估计、更少的干扰以及覆盖更大和更偏远地区的能力。无人机调查照片允许可重复和可量化的栖息地评估、侵占和其他非法活动的检测，并留下永久记录。

结论：总体而言，无人机为调查鳄鱼种群提供了一种有价值且具有成本效益的替代方案，具有令人信服的次要优势，尽管它们可能并不适用于所有情况和所有物种。

启示：我们为基于无人机的鳄鱼调查提出了一个标准化和优化的协议，可用于西非和全球鳄鱼的可持续保护计划。