Abstract
In 2018, wind energy grew 12% globally in response to offset greenhouse gas emissions (IEA, 2019). While land-based wind projects (LBW) still dominate the supply chain, offshore-based wind projects (OBW) are becoming more prevalent. With this increase in wind energy deployment, the probability of increased wildlife conflict also increases, particularly with bats. Wind turbines can impact certain bat species from collision events, especially during seasonal migration movements. Twenty-three of the 47 US bat species have been found as representative fatalities at LBW (AWWI, 2018). Bats and wind turbines are now unfortunately connected, due to the increase in wind turbine placements in bat migration and foraging corridors. Insectivorous bats are echolocating mammals that use ultrasonic frequencies to hunt and avoid obstacles in air space. Technology such as ultrasonic acoustic deterrents (UAD) devices that emit high frequency sound, have been used on LBW projects with mixed but generally positive results. UADs placed on wind turbines that cause echolocation disorientation within ensonified areas can help divert bats from wind energy turbine air space and help to reduce bat related collision fatalities. The objectives of this project were to identify mitigative steps to reduce bat fatalities at OBW using information gathered from LBW that have employed UADs. It was hypothesized that UAD deployment at wind energy facilities could reduce bat fatalities. A secondary objective was to determine abiotic factors that had effects on bat activity around wind turbines. A third objective was to use two echolocating mammals as proxy parameter comparisons to see if UADs would deter both groups of species from ensonfied areas similarly: bats and toothed whales (odontocetes). My assumptions were that UADs were effective at deterring bats from the ensonified areas of wind turbines and that high wind velocities, low barometric pressure and decreasing temperatures during seasonal migrations altered bat activity around wind turbines. Any successes from odontocete stranding event mitigation using aquatic UADs can be used as support for another echolocating mammal reacting to UAD use for deterrence from ensonified areas. I analyzed proprietary and published data based on field tested bat studies using UADs at several North American LBW, in collaboration with several wind energy organizations. Using generalized mixed modeling (GLMM), I identified abiotic variables that influence how and when bats interact with LBW. I compared these factors to wind energy sites that deployed UADs on some turbines and others were used as controls. As a smaller, secondary comparison, I evaluated odontocete stranding event data that deployed UADs to test if there was a feasible comparison proxy between two types of potential fatality events involving echolocating mammal species. For the first model, the GLMM results showed that presence of operational UADs on LBW treatment wind turbines was statistically significant (p <0.001) at reducing bat fatality events when compared to control wind turbines. For the second model, there was no statistically significant effects from any of the three abiotic variables on bat fatality reductions at treated LBW turbines. However, in model 3, average nightly wind speed was statistically significant at control LBW turbines. Due to insufficient data on odontocete stranding events and UAD deployment, this proxy was only used as anecdotal information. The results indicate that UADs are effective deterrents for reducing bat fatality events at LBW. Results also showed that wind speed was significant at wind turbines without deterrent technology. Nightly wind speed can act as an abiotic predictor variable on how bat activity reacts at LBW turbines. When looking to guide mitigative language for OBW, deploying UADs and monitoring for bat activity based on nightly wind fluctuations can influence bat fatality events.