Wildlife monitoring with unmanned aerial vehicles: Quantifying distance to auditory detection

Abstract

ABSTRACT There is growing application of small unmanned aerial vehicles (UAVs) for detecting, enumerating, and monitoring wildlife. However, little is known about how the sound from UAVs may be affecting wildlife being studied. We quantified sound levels of 2 UAVs to determine minimum altitudes they can fly before being aurally detected by wildlife. We tested a small quadcopter (SkyRanger; Aeryon Labs, Inc., Waterloo, ON, Canada) and a fixed‐wing platform (eBee; Sensefly Ltd., Cheseaux‐sur‐Lausanne, Vaud, Switzerland) at the University of Calgary in Calgary, Alberta, Canada, between 1000 and 1200 hours on 27 September 2014. We modeled sound propagation and attenuation in relation to the lower hearing thresholds for 3 game species and 2 species of predators. Results indicate that the UAV sound levels differed in the lower frequency ranges, but were otherwise similar above 1.25 kHz. The domestic cat (Felis silvestris catus) has the lowest hearing threshold, with the capacity to hear both UAVs from the furthest distance; whereas, the mallard (Anas platyrhynchos) has the greatest hearing threshold, which means UAVs can be closer before being aurally detected. Because flying height is related to image resolution, our results indicate that the ability to detect some wildlife species may be affected by the need to fly higher to minimize sound disturbance, potentially requiring higher resolution cameras than those currently used. Also, additional flight permitting may be required if modeling indicates a UAV must fly at a greater height to avoid a behavioral response by the target species. © 2016 The Wildlife Society.

Keywords

• drone
• hearing threshold
• sound
• UAV
• unmanned aerial vehicle