What Does the DEIS Say About Bats?
Short Version: The estimated mean bat fatality rate given in the Lava Ridge DEIS is 1.5 bats/MW/year, with a maximum of 7.4 bats/MW/year. Effective mitigation to protect bats includes siting turbines 1,000 feet or more away from irrigation canals, avoiding lighting that attracts bats, using acoustic deterrents, and avoiding operational activities that pose a threat to bat populations.
Detailed Summary: The DEIS looked in detail at the effect of the project on bat roosting habitat, and the effect of turbine operations on bat populations.
Bats need roosts for resting during short-term periods of inactivity. Different species of bats have different roosting needs, and some species may prefer to roost in one type of structure during the day and a different type of structure at night. Some species have additional requirements for long-term roost sites, which can be either maternity roosts or locations where bats hibernate during the winter.
To analyze the effects on bat populations, information was gathered over two years from both the Project area and from using a comparison to other wind facilities in similar ecosystems to create the fatality rate estimates for Lava Ridge. Fatality rates are not intended to be precise predictions but are presented to allow for a meaningful comparison between the alternatives presented in the DEIS.
Lava vents analyzed in the Project area have no noticeable aboveground features on the landscape and thus were unlikely to be used as bat features. Most of the lava tubes assessed had rocky outcrops or rock piles that also have low potential to be used for day roosting (because a bat would be exposed to heat, light, and inclement weather), but could provide suitable night roosts.
No bats or signs of bats (i.e., guano, staining, audible bat calls) were observed at any cave entrances in the Project area. Caves, lava tubes, and known roost sites would be avoided, and the effects to other roosting features (such as shrubs and trees) would not be considered irreversible because most of the habitat would be reclaimed and restored. Large areas of similar habitat would remain available in the broader landscape.
Putting The DEIS Analysis In Context
As shown below, the estimated mean bat fatality rate given in the Lava Ridge DEIS is 1.5 bats/MW/year, with a maximum of 7.4 bats/MW/year.
Overall, Lava Ridge’s estimated bat fatality rate appears to be lower than other wind projects. Based on the DEIS data along with the agreed upon mitigation measures, bat fatality rates may be on the lower end of the spectrum of values identified and less than other wind projects of similar scale.
Figure 1. Bat Fatality Estimates for Wind Energy Facilities in EISs with ≥50 MW and measuring in bat fatalities/MW/Yr.
What Steps Will MVE Take To Protect Bats?
To minimize impacts to bat species and to reduce the potential for significant adverse effects, MVE has developed strategies as outlined in the Bird and Bat Conservation Strategy (BBCS). As part of the BBCS, Tier 1, 2, and 3 studies were completed to characterize bat use in the siting corridors, assess the potential for the project to result in population-level effects to bat species of concern, and identify methods for measuring actual impacts following construction.
MVE would prioritize avoidance of riparian areas, wetlands, and other water bodies and would site turbines at least 1,000 feet from the irrigation canals, which would reduce the potential for bats to be exposed to turbines while foraging. Turbine lighting would be designed to avoid attracting birds or bats.
MVE would also implement curtailment measures to reduce bat fatalities by reducing turbine operations that pose the greatest threat to bat species. Because bats are more active at lower wind speeds, turbine fatality rates tend to be highest when speeds are low. Thus, to proactively reduce the risk of bats colliding with turbines, turbine blades would be feathered during the periods when bats are most active (within specified ranges defined based on species of concern). Feathering turbine blades prevents them from rotating (or greatly reduces their rotational speed).
Adaptive management measures also include the use of acoustic deterrents to reduce bat fatalities at operational turbines. These systems are effective, with an 18% to 78% reduction in the fatality rate. The committed mitigation measures and continual observations will reduce the fatality rates of species of bats throughout the life of the project. Compensatory mitigation may also be assessed by BLM, with funds dedicated to help research and improve bat habitat.