Strategic conservation efforts for cryptic species, especially bats, are hindered by limited understanding of distribution and population trends. Integrating long-term encounter surveys with multi-season occupancy models provides a solution whereby inferences about changing occupancy probabilities and latent changes in abundance can be supported. When harnessed to a Bayesian inferential paradigm, this modeling framework offers flexibility for conservation programs that need to update prior model-based understanding about at-risk species with new data. This scenario is exemplified by a bat monitoring program in the Pacific Northwestern United States in which results from 8 years of surveys from 2003 to 2010 require updating with new data from 2016 to 2018. The new data were collected after the arrival of bat white-nose syndrome and expansion of wind power generation, stressors expected to cause population declines in at least two vulnerable species, little brown bat (Myotis lucifugus) and the hoary bat (Lasiurus cinereus). We used multi-season occupancy models with empirically informed prior distributions drawn from previous occupancy results (2003-2010) to assess evidence of contemporary decline in these two species. Empirically informed priors provided the bridge across the two monitoring periods and increased precision of parameter posterior distributions, but did not alter inferences relative to use of vague priors. We found evidence of region-wide summertime decline for the hoary bat ( λ ^ = 0.86 ± 0.10) since 2010, but no evidence of decline for the little brown bat ( λ ^ = 1.1 ± 0.10). White-nose syndrome was documented in the region in 2016 and may not yet have caused regional impact to the little brown bat. However, our discovery of hoary bat decline is consistent with the hypothesis that the longer duration and greater geographic extent of the wind energy stressor (collision and barotrauma) have impacted the species. These hypotheses can be evaluated and updated over time within our framework of pre-post impact monitoring and modeling. Our approach provides the foundation for a strategic evidence-based conservation system and contributes to a growing preponderance of evidence from multiple lines of inquiry that bat species are declining.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/ece3.5612

Evidence of region-wide bat population decline from long-term monitoring and Bayesian occupancy models with empirically informed priors.

Land use and turbine technology influences on wind potential in the United States

Interactions of wind energy project siting, wind resource potential, and the evolution of the U.S. power system

With the expansion of wind energy, bird and bat fatalities have also increased. Once wind turbines are installed, the only effective impact-reduction measure consists of operational curtailment – documented for bats but not for birds. We measured curtailment effects in an opportune before-after, control-impact (BACI) experimental design involving two wind projects monitored for fatalities using scent detection dogs and for nocturnal passage rates using thermal imaging during fall migration, where one project continued operating and the other shut down from the peak of migration to the study’s end. We also compared bird fatality rates based on humans averaging 5-day search intervals among wind turbines of varying operable status, including operable, inoperable, vacant tower, and empty pad. Wind turbine curtailment in the BACI study had no significant effect on bird passage rates or fatality rates, whereas it significantly reduced bat passage rates and reduced bat fatality finds to 0. In the study of variable operable status among wind turbines, birds estimated to have died within 15 days of discovery averaged 35% more fatalities/MW at inoperable than at operable wind turbines, and fatalities declined substantially at vacant towers and empty pads. Of species represented by bird fatalities, 79% were found at inoperable wind turbines, including all 6 red-tailed hawk (Buteo jamaicensis) fatalities. Because the migration season is relatively brief, a seasonal curtailment strategy would greatly reduce bat fatalities while losing only a small fraction of a wind project’s annual energy generation, but it might not benefit many species of birds.

https://wildlife.onlinelibrary.wiley.com/doi/pdf/10.1002/jwmg.21844

Effects of Wind Turbine Curtailment on Bird and Bat Fatalities

Assessing fatality minimization for hoary bats amid continued wind energy development

The development and expansion of wind energy is considered a key global threat to bat populations. Bat carcasses are being found underneath wind turbines across North and South America, Eurasia, Africa, and the Austro-Pacific. However, relatively little is known about the comparative impacts of techniques designed to modify turbine operations in ways that reduce bat fatalities associated with wind energy facilities. This study tests a novel approach for reducing bat fatalities and curtailment time at a wind energy facility in the United States, then compares these results to operational mitigation techniques used at other study sites in North America and Europe. The study was conducted in Wisconsin during 2015 using a new system of tools for analyzing bat activity and wind speed data to make near real-time curtailment decisions when bats are detected in the area at control turbines (N = 10) vs. treatment turbines (N = 10). The results show that this smart curtailment approach (referred to as Turbine Integrated Mortality Reduction, TIMR) significantly reduced fatality estimates for treatment turbines relative to control turbines for pooled species data, and for each of five species observed at the study site: pooled data (-84.5%); eastern red bat (Lasiurus borealis, -82.5%); hoary bat (Lasiurus cinereus, -81.4%); silver-haired bat (Lasionycteris noctivagans, -90.9%); big brown bat (Eptesicus fuscus, -74.2%); and little brown bat (Myotis lucifugus, -91.4%). The approach reduced power generation and estimated annual revenue at the wind energy facility by ≤ 3.2% for treatment turbines relative to control turbines, and we estimate that the approach would have reduced curtailment time by 48% relative to turbines operated under a standard curtailment rule used in North America. This approach significantly reduced fatalities associated with all species evaluated, each of which has broad distributions in North America and different ecological affinities, several of which represent species most affected by wind development in North America. While we recognize that this approach needs to be validated in other areas experiencing rapid wind energy development, we anticipate that this approach has the potential to significantly reduce bat fatalities in other ecoregions and with other bat species assemblages in North America and beyond.

A smart curtailment approach for reducing bat fatalities and curtailment time at wind energy facilities.

The development and expansion of wind energy is considered a key threat to bat populations in North America and globally. Several approaches to mitigating the impacts of wind energy development on bat populations have been developed, including curtailing wind turbine operation at night during lower wind speeds when bats are thought to be more active. Blanket curtailment approaches have shown substantial promise in reducing bat fatalities at wind energy facilities, but they also reduce the amount of energy extracted from the wind by turbines. A related approach, referred to as smart curtailment, uses bat activity and other variables to predict when bats will be at the greatest risk at a given wind facility. In some contexts, a smart curtailment approach might reduce bat fatalities while also reducing energy loss relative to blanket curtailment. However, it has not been clear how to compare blanket curtailment and smart curtailment approaches in terms of annual energy production at wind facilities. Here, we describe a new approach to simulating the influence of blanket and smart curtailment approaches on energy production at wind energy facilities, and demonstrate the approach using 6 wind energy development areas in the Canadian province of Alberta. We show how stakeholders involved can explore the potential influences of various kinds of bat activity on energy production. We present the results of our Alberta analysis and conclude with some caveats and recommendations for future work on simulating the influences of bat curtailment on energy production at wind energy facilities. 

Stephen R. Lindsay

Papers

A smart curtailment approach for reducing bat fatalities and curtailment time at wind energy facilities.

Simulating the influences of bat curtailment on power production at wind energy facilities