Autonomous drones are a viable tool for acoustic bat surveys

Abstract

Acoustic surveys of bats are currently limited by the detection range of ultrasound microphones. This makes it difficult to survey bats at height, over water, or in other hard to reach locations.Drones, also known as UAVs or UASs, are becoming more affordable and feature rich, resulting in more uptake in conservation, primarily for aerial imagery. In this paper we address current limitations to acoustic bat surveys by developing three autonomous drones for surveying bats; a plane, quadcopter and boat. All three are capable of moving autonomously from one waypoint to another while carrying a bat detector to record bats and are all low cost (under US$950) with large operational ranges that make them suited to aerial transect work.Initial testing highlighted ultrasound noise generated by the drones as a major issue for recording bats from these systems. This was mitigated through iterative design of the microphone placement and the vehicles themselves. Subsequent testing in real world settings, in the presence of bats, demonstrated that bats could be recorded under autonomous navigation and that the ultrasound interference could be reduced to a negligible level.Autonomous drones offer an exciting new tool in the tool box of bat workers and researchers.They allow us to study areas previously inaccessible on foot, as well as at heights that have previously been inaccessible. We also discuss current limitations to this technology, including legal considerations, hidden costs and potential impacts on bat behaviour.

Drone exploration of bat echolocation: A UAV‐borne multimicrophone array to study bat echolocation

“…We further show that the behavioral impact of the UAV is limited, given that all four species approach the microphone array within 1 m and all four species emit recordable feeding buzzes. Compared to previous reports, we use a much greater distance between the UAV and the microphones (August & Moore, 2019 ; Ednie et al, 2021 ; Fu et al, 2018 ; Kloepper & Kinniry, 2018 ; Michez et al, 2021 ), which reduces the noise substantially and very likely also the behavioral impact of the UAV considerably. Previous studies report avoidance behavior and a clear reduction in bat activity in the presence of UAVs with no reports of the recorded foraging that we observe for all recorded species (Ednie et al, 2021 ; Fu et al, 2018 ; Kloepper & Kinniry, 2018 ; Kuhlmann et al, 2022 ).…”

“…Several studies have investigated the potential of UAVs as bat survey tools (i.e., single microphone presence/absence data) and they have addressed these concerns with varying results. All studies use mitigation efforts to reduce noise by shielding the microphone (August & Moore, 2019 ; Ednie et al, 2021 ; Fu et al, 2018 ; Kloepper & Kinniry, 2018 ) and/or suspending the microphone at some distance from the UAV (Michez et al, 2021 ). Both solutions yield clear improvements, but proper noise quantification is lacking.…”

Noninvasive Technologies for Primate Conservation in the 21st Century

“…Combining technologies can further improve species monitoring. Drones have already been equipped with microphones that capture bat and bird sounds (August and Moore, 2019;Wilson et al, 2017), and there are plans to diversify drone-acoustic applications to monitor terrestrial species, such as gibbons (Borchers, pers. com.).…”

Miniaturization eliminates detectable impacts of drones on bat activity

“…The choice of UAV type for wildlife research is a critical decision considering that the UAV rotary models available differ widely in power source, dimension, cost, flight parameters and battery life. UAVs also emit variable ultrasonic frequencies, ranging from 4 to 45 kHz (Broset, 2018; August & Moore, 2019; Jokisch & Fischer, 2019). UAVs emit higher frequency signals when climbing and lower frequencies when shifting positions relative to hovering (Jokisch & Fischer, 2019).…”