Optimizing UAS for Bat Activity Monitoring near wind turbines : investagating deterrent and habituation effects

Abstract

The protection of bats (Chiroptera) around wind turbines requires a better understanding of bat activity in the vicinity of these structures. Currently, stationary nacelle monitoring is used to determine bat activity levels at greater height. However, this method has limitations as it covers only 4% of the risk area for bats with echolocation calls of 40 kHz (assuming a 60 m blade length). Additional data could be collected by Unmanned Arial System (UAS), to reduce bat fatalities while optimizing shutdown times for individual wind turbines and improve the planning of new wind turbine installations. The goal of this study is to investigate whether optimized UAS have a deterrent or attraction effect on bats and whether bats become accustomed to the presence of UAS over time.

In a previous study in 2022, we recorded the bat activity levels starting 30 minutes after sunset until 4 hours later in altogether 24 nights. An acoustical bat detector was installed at two meters height facing vertically upwards. Subsequently, we recorded bat activity while a large multicopter UAS was hovering in 20 meters height above the bat detector and without the UAS (control). Bat activity was significantly lower in presence of the UAS, however this deterrent effect was small. We assume that this small effect could be explained by the experimental set-up, since bats cannot fly near the multicopter due to strong air turbulence and thus avoid UAS.

In the present study we collected data using an optimized multicopter, with reduced acoustic and light emissions. While keeping the original bat detector facing upwards for the comparability of the results, we installed a second bat detector directed towards the ground 10 meters below the UAS, hovering at 22 meters height. This setup represents real-life conditions, as it will be suspended 10 meters below the UAS in a downward-facing orientation. Further, we studied the habituation effect of bats towards the multicopter by analyzing the effect of time on bat activity.

We expect no or a smaller deterrent due to the optimized set-up and technical changes made to the multicopter. We further expect no difference in bat activity between the recordings taken by the bat detector directed towards the ground and the control. If this method does not exhibit a deterrent effect, we will be able to collect data on bat activity at the upper end of the wind turbine for the first time.