Low-budget ready-to-fly unmanned aerial vehicles: an effective tool for evaluating the nesting status of canopy-breeding bird species

Remotely controlled, unmanned aerial vehicles (UAVs) promise to be of high potential for a variety of applications in ecological and behavioural research. Off-the-shelf solutions have recently become available for civil use at steeply decreasing costs. In this study, we explored the utility of an UAV equipped with an on-board camera (14 megapixel photo and 1920 x 1080 pixel video resolution) in assessing the breeding status, offspring number and age of a canopy-breeding bird species, the hooded crow Corvus [corone] cornix. We further quantified performance and potential time savings using the UAV versus inspection with alternative approaches (optical instruments, camera on a telescopic rod, tree climbing). Nesting status, number and approximate age of nestlings could be assessed with good success in all 24 attempts using the UAV. Eighty-five percent of the time required for inspection by climbing could be saved. Disturbance was moderate and lower than caused by climbing or using a camera on a telescopic rod. Additionally, UAV usage avoided tree damage and circumvented health risks associated with tree-climbing.