Monitoring active Osprey nests with drones is more time-efficient and less disturbing than conventional methods

Drones are used to monitor bird nesting sites at less accessible locations, such as on cliffs, human infrastructure, or within the tree canopy. While there are a growing number of studies documenting avian behavioral responses to various drones, there is a continued need to monitor taxa-specific responses to different drone models. We explored both the time efficiency and impact of different nest survey methods (drones, nest climbing, and observations from a bucket truck) and different drone model sizes (small, medium, large) on the nest defense behavior of breeding Ospreys. We conducted 166 surveys (126 drone, 25 climbing, 15 bucket truck) at 85 active nests across three nesting stages. We found variation in 4 of 6 pre-defined behavioral categories, namely for calling, flying, at nest, and perching behaviors with survey method, sex, and nest stage. Females were more responsive to all survey methods compared to males and engaged in nest-protection behaviors most frequently during incubation. Ospreys spent greater time at their nests during drone surveys compared to other methods. Agitated calling and flying were also less frequent during drone surveys. We recorded defensive behaviors across all survey types and there were no strikes on drones or researchers. Drone size appeared to influence behavior, with female Ospreys spending, on average, 18% of survey time calling when surveyed with medium-sized drone compared to smaller (8%) or larger (6%) models. Surveys with drones took less time to complete compared to the other methods tested. Based on our findings, drones appear to be the best choice for monitoring Osprey nests as they are adaptable, time efficient, and result in less apparent disturbance to nesting Ospreys than other methods tested. Our research aids in setting best practices, optimizing drone size, and developing evidence-driven approaches for monitoring avian nests across a variety of landscapes and contexts.无人机（Drone）可用于监测难以抵达区域的鸟类巢址，例如悬崖、人工构筑物或树冠内部。尽管目前已有越来越多的研究记录了鸟类对各类无人机的行为响应，但仍需持续监测不同类群对不同型号无人机的特异性响应。本研究同时探究了三类巢址调查方法（无人机调查、攀巢调查、高空作业斗臂车观测）以及不同尺寸型号的无人机（小型、中型、大型）对繁殖期鹗（Osprey）巢防御行为的影响，并对比了各类方法的时间效率。本研究在三个繁殖阶段的85个活跃巢址中共开展了166次调查，其中无人机调查126次、攀巢调查25次、斗臂车观测15次。本研究发现，在预设的6类行为类别中，鸣叫、飞行、留巢与停栖这4类行为会随调查方法、个体性别及繁殖阶段的不同而出现显著差异。相较于雄性鹗，雌性对所有调查方法的响应更为强烈，且在孵卵阶段的巢防御行为发生频率最高。与其他调查方法相比，无人机调查中鹗在巢址停留的时间更长。无人机调查中，鹗的急促鸣叫与飞行行为的发生频率也更低。所有调查类型中均记录到了防御行为，但未发生鹗攻击无人机或研究人员的情况。无人机尺寸似乎会对鹗的行为产生影响：使用中型无人机开展调查时，雌性鹗平均会将18%的调查时间用于鸣叫，而使用小型或大型无人机时，该占比分别为8%与6%。相较于本次测试的其他调查方法，无人机调查的完成耗时更短。基于本研究结果，无人机是监测鹗巢址的最优选择：其适应性强、耗时短，且相较于本次测试的其他方法，对繁殖期鹗的干扰更为轻微。本研究有助于制定最佳调查规范、优化无人机尺寸，并为不同景观与场景下的鸟类巢址监测提供循证方法。