Using echolocation monitoring to model bat occupancy and inform mitigations at wind energy facilities

Abstract

Fatalities of migratory bats, many of which use low frequency (<35 kHz; LowF) echolocation calls, have become a primary environmental concern associated with wind energy development. Accordingly, strategies to improve compatibility between wind energy development and conservation of bat populations are needed. We combined results of continuous echolocation and meteorological monitoring at multiple stations to model conditions that explained presence of LowF bats at a wind energy facility in southern California. We used a site occupancy approach to model nightly LowF bat presence while accounting for variation in detection probability among echolocation detectors and heights. However, we transposed the spatial and temporal axes of the conventional detection history matrix such that occupancy represented proportion of nights, rather than monitoring points, on which LowF bats were detected. Detectors at 22 m and 52 m above ground had greater detection probabilities for LowF bats than detectors at 2 m above ground. Occupancy of LowF bats was associated with lower nightly wind speeds and higher nightly temperatures, mirroring results from other wind energy facilities. Nevertheless, we found that building separate models for each season and considering solutions with multiple covariates resulted in better fitting models. We suggest that use of multiple environmental variables to predict bat presence could improve efficiency of turbine operational mitigations (e.g., changes to cut‐in speeds) over those based solely on wind speed. Increased mitigation efficiencies could lead to greater use of mitigations at wind energy facilities with benefits to bat populations. © 2011 The Wildlife Society.

Estimating Bat and Bird Mortality Occurring at Wind Energy Turbines from Covariates and Carcass Searches Using Mixture Models

“…Most of the models hitherto used to mitigate bat collisions at wind turbines predict the bat collision rate qualitatively, e.g. as a probability of bats being active [40] or as an index of bat activity [41]. Such qualitative models allow for a mitigation of collisions, but they do not allow the effectiveness of the mitigation strategies to be measured since they provide no information on how the bat activity indices transform quantitatively into collision rates.…”

Impacts of Wind Energy Development on Bats: A Global Perspective

“…5. Future operational mitigation experiments should be designed to determine which factors (e.g., habitat, insect occurrence, temperature, wind, humidity, moon illumination) or combination of factors (Weller and Baldwin 2012) will best improve predictability of bat fatalities, while minimizing economic costs. Alternative mitigation approaches to operational adjustments should be proven equally or more effective at reducing bat fatalities at operating wind facilities before being accepted as viable mitigation approaches.…”

Site occupancy of foraging bats on landscapes of managed pine forest

“…The resulting false absences (species is present but not detected; MacKenzie, 2005) may influence results and inferences unless accounted for in analyses (Gu and Swihart, 2004). Because bats are imperfectly detected and detection may be influenced by habitat characteristics, occupancy modeling has recently been applied to acoustic surveys for bats (Amelon, 2007;Gorreson et al, 2008;Hein et al, 2009;Weller and Baldwin, 2012;Yates and Muzika, 2006). Occupancy modeling allows simultaneous investigation of factors influencing occupancy and detection probabilities, improving the ability to make inferences about species use of landscape features (MacKenzie et al, 2002;MacKenzie, 2005).…”