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

Abstract

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 four of six 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.