Evaluation of unmanned aerial vehicles for surveys of lek‐mating grouse

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Evaluation of unmanned aerial vehicles for surveys of lek-mating grouse

Before drones (umanned aerial vehicles) can replace manned aircraft in wildlife surveys, best practices need to be developed that maximize the data obtained while minimizing disturbance to the focal wildlife. Our study contributes to the development of best practices for the use of drones for monitoring populations of upland, lek-mating grouse of conservation concern, and provides recommendations for optimal drone size, camera angle, and height of flight for maximizing detection.

Abstract

Unmanned aerial vehicles (UAVs), or drones, are being utilized by wildlife biologists to monitor populations of birds and mammals. However, the reaction of wildlife to drones varies by species, so a preliminary evaluation must be conducted to determine if the target species can be detected via drone footage and to determine how the target species will react to drone presence. Lek-mating prairie-chickens (Tympanuchus spp.) seem amenable to drone-based surveys because they are relatively large and display in groups on elevated sites with sparse vegetation. The goal of our study was to determine what flight characteristics maximize prairie-chicken detection on drone video footage, to document the birds’ reactions to the drones, and to compare how the noise produced by the drones compares to ambient sounds. We tested 3 sizes of rotary-winged drones, flown at 3 heights, with 3 different camera angles by flying over known prairie-chicken leks. We determined that >65% of prairie-chickens present were detected using video footage at a height of 100 m with a 10° camera angle. Drones of different sizes had similar detectability. However, observers in blinds adjacent to leks routinely detected more birds than were detected on drone footage (detection on drone footage was 39.7 ± 9.6% of birds present). Prairie-chickens flushed in 96% of trials when a drone was flown over display locations. Time to return to the lek following drone disturbance was similar to prairie-chickens’ reactions to natural predators. Prairie-chickens flushed when drone sound levels were comparable to ambient noise. Developing guidelines for the ethical use of drones in wildlife research will require quantifying the amount of taxa-specific disturbance caused by drones. Our study begins to close this knowledge gap by documenting disturbance to upland, lek-mating grouse of conservation concern, and suggests that the focal species’ reaction to aerial predators may provide clues as to how that species may react to drones.

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