Altamont Pass Research Articles

Understanding fatality patterns and sex ratios of Brazilian free-tailed bats (Tadarida brasiliensis) at wind energy facilities in western California and Texas

Background Operation of wind turbines has resulted in collision fatalities for several bat species, and one proven method to reduce these fatalities is to limit wind turbine blade rotation (i.e., curtail turbines) when fatalities are expected to be highest. Implementation of curtailment can potentially be optimized by targeting times when females are most at risk, as the proportion of females limits the growth and stability of many bat populations. The Brazilian free-tailed bat (Tadarida brasiliensis) is the most common bat fatality at wind energy facilities in California and Texas, and yet there are few available data on the sex ratios of the carcasses that are found. Understanding the sex ratios of fatalities in California and Texas could aid in planning population conservation strategies such as informed curtailment. Methods We used PCR to determine the sex of bat carcasses collected from wind energy facilities during post-construction monitoring (PCM) studies in California and Texas. In California, we received samples from two locations within the Altamont Pass Wind Resource Area in Alameda County: Golden Hills (GH) (n = 212) and Golden Hills North (GHN) (n = 312). In Texas, we received samples from three wind energy facilities: Los Mirasoles (LM) (Hidalgo County and Starr County) (n = 252), Los Vientos (LV) (Starr County) (n = 568), and Wind Farm A (WFA) (San Patricio County and Bee County) (n = 393). Results In California, the sex ratios of fatalities did not differ from 50:50, and the sex ratio remained stable over the survey years, but the seasonal timing of peak fatalities was inconsistent. In 2017 and 2018, fatalities peaked between September and October, whereas in 2019 and 2020 fatalities peaked between May and June. In Texas, sex ratios of fatalities varied between locations, with Los Vientos being female-skewed and Wind Farm A being male-skewed. The sex ratio of fatalities was also inconsistent over time. Lastly, for each location in Texas with multiple years studied, we observed a decrease in the proportion of female fatalities over time. Discussion We observed unexpected variation in the seasonal timing of peak fatalities in California and differences in the sex ratio of fatalities across time and facility location in Texas. In Texas, proximity to different roost types (bridge or cave) likely influenced the sex ratio of fatalities at wind energy facilities. Due to the inconsistencies in the timing of peak female fatalities, we were unable to determine an optimum curtailment period; however, there may be location-specific trends that warrant future investigation. More research should be done over the entirety of the bat active season to better understand these trends in Texas. In addition, standardization of PCM studies could assist future research efforts, enhance current monitoring efforts, and facilitate research on post-construction monitoring studies.

Deploying Taller Turbines in Complex Terrain: A Hill Flow Study (HilFlowS) Perspective

Terrain-induced flow acceleration is presented for the summertime, peak power season at Lawrence Livermore National Laboratory’s Site 300 for the Hill Flow Study (HilFlowS). HilFlowS, designed as an adjunct field campaign to the Department of Energy’s Second Wind Forecasting Improvement Project (WFIP2), provides wind profile observations at a second location in complex terrain for validating numerical atmospheric model simulations and for better understanding flow behavior over hills for wind power generation. One unique feature of HilFlowS was the inclusion of an undergraduate university student who helped plan and execute the experiment as well as analyze wind data from two remote sensing laser detection and ranging (lidar) instruments deployed along parallel ridgelines. HilFlowS examines the trend of building higher into the atmosphere for the purpose of increasing wind turbine power production and evaluates the wind resource in the Altamont Pass Region of Northern California for a set of wind turbines of differing hub-heights and rotor-disk diameters found in the area. The wind profiles show strongly channeled onshore flow above both hills, enhanced by strong subsidence aloft, which produces a wind maximum (Umax) around z = 10 m and strong negative shear throughout all of the evaluated rotor-disks for much of the summer wind season. Under these conditions, shear becomes more negative with increasing hub-height and increasing rotor-disk size. Rotor-disk equivalent wind speed (Uequiv), a measure of the average wind speed across the entire rotor-disk, is compared to hub-height, rotor length, and rated capacity factor for the set of turbines. Uequiv is most closely related to turbine hub-height and is negatively correlated given the low altitude of Umax. Based on these results, building the largest capacity, large rotor-disk wind turbine at the lowest possible hub-height appears to provide turbines in the Altamont with a fast, near-surface, onshore wind resource during the peak power season.

Breeding Density and Collision Mortality of Loggerhead Shrike (Lanius ludovicianus) in the Altamont Pass Wind Resource Area

Loggerhead shrike (Lanius ludovicianus) has declined across most or all of its geographic range. The species’ raptorial behavior requires maintenance of large territories, which means populations of breeding shrikes require large areas of habitat and are therefore sensitive to habitat loss and habitat fragmentation. We estimated breeding densities of loggerhead shrikes in the Altamont Pass Wind Resource Area (APWRA), California, where annual shrike mortality caused by wind turbine collisions was high until just before our study began in 2016. Based on surveys across an annual average 50 randomized sampling plots in 2016–2019, we estimated an average 129 breeding pairs/year across the 167.6-km2 APWRA. Relative to the size of the study area, density in the APWRA was relatively high compared to densities reported from other study sites across North America. It was higher than predicted by application of the Partners in Flight estimator, which was based on Breeding Bird Surveys along roads. We also found that loggerhead shrikes in the APWRA were limited by the availability of nest substrate and by California ground squirrels (Otospermophilus beecheyi) and their burrow complexes, which have keystone effects on vegetation and wildlife in the APWRA. To most effectively conserve loggerhead shrikes in the APWRA, wind turbine mortality should be minimized, ground squirrels conserved instead of eradicated as pests, and appropriate trees and shrubs cultivated where they are needed.

Estimating wind turbine fatalities using integrated detection trials

ABSTRACTFatality monitoring at wind projects requires carcass detection trials to adjust fatality estimates for the proportion of fatalities not found. However, detection trials vary greatly in metric, duration, carcass monitoring schedule, species, number placed, state of decomposition, whether placed within or outside search areas, and other factors. We introduce a new approach for estimating fatalities by quantifying overall detection rates rather than separate rates for searcher detection error and carcass persistence, and by leaving placed and found fatality carcasses undisturbed throughout monitoring. We placed 2 fresh‐frozen bird carcasses weekly at random sites within fatality search areas and on randomized days Monday–Friday at Sand Hill and Santa Clara wind projects, Altamont Pass Wind Resource Area, California, USA. To estimate detection rates, we used logit regression to fit detection outcomes on body mass, which served as an axis of similitude between placed trial carcasses and fatality finds. Adjusted carcass placement rates among species detected by searchers regressed on true placement rates with a slope of 1.0 so long as sufficient numbers of trial carcasses were placed, thus validating our approach as an unbiased estimator. Our approach generally estimated lower fatality rates than did conventional approaches, the latter of which demonstrated biases in searcher detection rates and carcass persistence rates whether based on proportion of carcasses remaining or mean days to removal. Our approach also revealed detection errors that highlight the difficulty of finding and identifying the remains of dead animals, and which warrant routine reporting. Despite averaging only a 5‐day search interval on intensively grazed annual grasslands where ground visibility was usually high, our experienced fatality monitors averaged 4.3 searches/first carcass detection, failed to detect 25% of 75 species represented by placed carcasses, and misidentified carcasses to species among 44% of species detected. Estimates of time since death also suffered bias and large error. Our approach more realistically simulates carcass detection probabilities associated with fatality monitoring, is less costly, facilitates hypothesis testing, eliminates multiple sources of error and bias suspected of conventional methods, and enables quantification of errors in estimated time since death, species identifications, and false negative findings. © 2018 The Wildlife Society.

Long search intervals underestimate bird and bat fatalities caused by wind turbines

ABSTRACTBird and bat fatality estimates based on scientific monitoring are used to assess and compare impacts among wind energy projects. Fatality estimates are influenced by multiple factors, including variation in methodology. Variation in the interval between fatality searches exemplifies a monitoring decision that can potentially confound comparison of fatality estimates. A study at the Sand Hill portion of the Altamont Pass Wind Resource Area, California, USA, provided the first opportunity to compare fatality‐rate estimates derived from 2 independent, experienced monitoring teams searching the same wind turbines at 2 different periodic intervals. Over 30 months of monitoring the same wind turbines, April 2012–October 2014, searches averaging 5‐day intervals detected 308 additional fatalities (of 431 fatalities total) representing 20 additional species (of 32 species total) compared with the searches averaging 39‐day intervals. Body mass explained most of the variation in discrepant fatality detections between the 2 search intervals, with the 39‐day interval searches detecting only 10% of the bats and birds of 10–40 g that were found by the 5‐day interval searches. The 39‐day search interval produced an estimate of annual bird fatalities/MW that was 39% lower than the estimate produced from the 5‐day search interval. The 39‐day search interval also resulted in many more species identification errors and greater errors in estimated time since death. The average search interval used in fatality monitoring strongly influences fatality estimates; long intervals can contribute to false impressions that wind projects have small or negligible effects on small birds and bats. © 2017 The Wildlife Society.

Golden Eagle fatalities and the continental-scale consequences of local wind-energy generation.

Renewable energy production is expanding rapidly despite mostly unknown environmental effects on wildlife and habitats. We used genetic and stable isotope data collected from Golden Eagles (Aquila chrysaetos) killed at the Altamont Pass Wind Resource Area (APWRA) in California in demographic models to test hypotheses about the geographic extent and demographic consequences of fatalities caused by renewable energy facilities. Geospatial analyses of δ2 H values obtained from feathers showed that ≥25% of these APWRA-killed eagles were recent immigrants to the population, most from long distances away (>100 km). Data from nuclear genes indicated this subset of immigrant eagles was genetically similar to birds identified as locals from the δ2 H data. Demographic models implied that in the face of this mortality, the apparent stability of the local Golden Eagle population was maintained by continental-scale immigration. These analyses demonstrate that ecosystem management decisions concerning the effects of local-scale renewable energy can have continental-scale consequences.

Measuring turbine inflow with vertically-profiling lidar in complex terrain

Two Laser and Detection Ranging (lidar) units were deployed in the Altamont Pass region of California to study complex flow dynamics at a moderately complex terrain wind farm. The lidars provided wind measurements at the base and along the slope of a 140m tall ridge and captured air flow as it moved up and along the ridge towards an unwaked turbine under varying stability conditions. Elevation enhanced wind speed during well-mixed or near-neutral conditions at the top of the ridge; however, the hill “speed-up” was smaller than expected during stable conditions. At these times the upwind terrain played a significant role in local flow variability as did terrain features within the wind farm. The observations were next analyzed to assess the ability of using vertically-profiling lidar in complex terrain to measure free-stream inflow for evaluating power generation response. Better agreement between the lidar wind speed and expected power was found once the lidar measurements had been adjusted for stability-dependent hill speed-up effects. This suggests that vertically-profiling lidar can be used in complex terrain to measure inflow if the terrain-induced flow features are also considered.

Wind power curve modeling in complex terrain using statistical models

The simplest power curves model wind power only as a function of the wind speed at the turbine hub height. While the latter is an essential predictor of power output, wind speed information in other parts of the vertical profile, as well as additional atmospheric variables, are also important determinants of power. The goal of this work was to determine the gain in predictive ability afforded by adding wind speed information at other heights, as well as other atmospheric variables, to the power prediction model. Using data from a wind farm with a moderately complex terrain in the Altamont Pass region in California, we trained three statistical models—a neural network, a random forest and a Gaussian process model—to predict power output from various sets of aforementioned predictors. The comparison of these predictions to the observed power data revealed that considerable improvements in prediction accuracy can be achieved both through the addition of predictors other than the hub-height wind speed and the use of statistical models. To our knowledge, the use of the Gaussian process model in this context is new, in contrast to neural networks and random forests. The advantage of this model over the other two models is that it provides a much more natural way to estimate the uncertainty associated with its predictions. In addition, this study presents one of the most comprehensive analyses to date of the relative importance of various wind power curve inputs.

Nesting burrowing owl density and abundance in the Altamont Pass Wind Resource Area, California

About 600 burrowing owls (Athene cunicularia) are killed annually at wind turbines in the Altamont Pass Wind Resource Area (APWRA), California, USA. Understanding the biological significance of this toll requires population data, including an estimate of the number of breeding pairs in the APWRA. An empirical model of breeding density predicted 35–75 pairs within the 16,760 ha of the APWRA, but that prediction proved low in spring 2011, when we detected 78 breeding pairs of burrowing owls in 46 randomly selected plots totaling 2,563 ha. We estimated that 3.201 breeding pairs/km2 occupied the 46 plots we surveyed in April–May. Extrapolating this density to the area of the APWRA led to an estimate of 537 pairs (90% CI = 320–753 pairs) across the APWRA, or 10× the model prediction. Counts of chicks emerged from burrows averaged 1.2 chicks/nest on the 46 plots, but these counts were minimum numbers. We estimated the APWRA supported at least 1,836 burrowing owls in 2011 (90% CI = 1,082–2,590), indicating the local population could conceivably be the sole source of fatalities attributed to wind turbines in the APWRA. Measures to conserve burrowing owls in the APWRA could include ground squirrel conservation and repowering to safer wind turbine models and careful siting to avoid areas densely populated with burrowing owls. More generally, management decisions based on comparisons of breeding-pair density should also consider whether the density estimates were made in habitat fragments, sites selected for known high density, or in randomly or systematically selected plots sampling large areas, because the type of study area strongly influences the density estimate. © 2013 The Wildlife Society.

Challenges and opportunities for animal conservation from renewable energy development

[Extract] Global climate change is among the greatest threats confronting both human and natural systems (IPCC, 2007). A substantial component of greenhouse gas (GHG) emissions is from energy production, generated via the burning of fossil fuels, especially coal, natural gas and refined petroleum. Given that reduction in global energy consumption is unlikely over the next century or so, renewable energy generation has been proposed as a low-carbon alternative to limit GHG emissions. Consequently, many national and regional governments have set targets for renewable energy manufacture and use (e.g. '20% Wind Energy by 2030' – DoE, 2008; EU, 2009). Nevertheless, despite the benefits associated with reducing carbon emissions, renewable energy development itself has important, sometimes severe, implications for the conservation of biodiversity that should not be ignored. A central challenge and opportunity for animal conservation is to understand and manage environmental problems associated with the rapid growth in renewable energy production, while simultaneously maintaining progress toward reducing dependence on fossil fuels.

Comparing bird and bat fatality‐rate estimates among North American wind‐energy projects

AbstractEstimates of bird and bat fatalities are often made at wind‐energy projects to assess impacts by comparing them with other fatality estimates. Many fatality estimates have been made across North America, but they have varied greatly in field and analytical methods, monitoring duration, and in the size and height of the wind turbines monitored for fatalities, and few benefited from scientific peer review. To improve comparability among estimates, I reviewed available reports of fatality monitoring at wind‐energy projects throughout North America, and I applied a common estimator and 3 adjustment factors to data collected from these reports. To adjust fatality estimates for proportions of carcasses not found during routine monitoring, I used national averages from hundreds of carcass placement trials intended to characterize scavenger removal and searcher detection rates, and I relied on patterns of carcass distance from wind turbines to develop an adjustment for variation in maximum search radius around wind turbines mounted on various tower heights. Adjusted fatality rates correlated inversely with wind‐turbine size for all raptors as a group across the United States, and for all birds as a group within the Altamont Pass Wind Resource Area, California. I estimated 888,000 bat and 573,000 bird fatalities/year (including 83,000 raptor fatalities) at 51,630 megawatt (MW) of installed wind‐energy capacity in the United States in 2012. As wind energy continues to expand, there is urgent need to improve fatality monitoring methods, especially in the implementation of detection trials, which should be more realistically incorporated into routine monitoring. © 2013 The Wildlife Society

The avian and wildlife costs of fossil fuels and nuclear power

Environmentalists and environmental scientists have criticized wind energy in various forums for its negative impacts on wildlife, especially birds. This article highlights that nuclear power and fossil-fuelled power systems have a host of environmental and wildlife costs as well, particularly for birds. Therefore, as a low-emission, low-pollution energy source, the wider use of wind energy can save wildlife and birds as it displaces these more harmful sources of electricity. The paper provides two examples: one relates to a calculation of avian fatalities across wind electricity, fossil-fueled, and nuclear power systems in the entire United States. It estimates that wind farms are responsible for roughly 0.27 avian fatalities per gigawatt-hour (GWh) of electricity while nuclear power plants involve 0.6 fatalities per GWh and fossil-fueled power stations are responsible for about 9.4 fatalities per GWh. Within the uncertainties of the data used, the estimate means that wind farm-related avian fatalities equated to approximately 46,000 birds in the United States in 2009, but nuclear power plants killed about 460,000 and fossil-fueled power plants 24 million. A second example summarizes the wildlife benefits from a 580-MW wind farm at Altamont Pass in California, a facility that some have criticized for its impact on wildlife. The paper lastly highlights other social and environmental benefits to wind farms compared to other sources of electricity and energy.

Quantifying the health and environmental benefits of wind power to natural gas

How tangible are the costs of natural gas compared to the benefits of one of the fastest growing sources of electricity – wind energy – in the United States? To answer this question, this article calculates the benefits of wind energy derived from two locations: the 580MW wind farm at Altamont Pass, CA, and the 22MW wind farm in Sawtooth, ID. Both wind farms have environmental and economic benefits that should be considered when evaluating the comparative costs of natural gas and wind energy. Though there are uncertainties within the data collected, for the period 2012–2031, the turbines at Altamont Pass will likely avoid anywhere from $560 million to $4.38 billion in human health and climate related externalities, and the turbines at Sawtooth will likely avoid $18 million to $104 million of human health and climate-related externalities. Translating these negative externalities into a cost per kWh of electricity, we estimate that Altamont will avoid costs of 1.8–11.8 cents/kWh and Sawtooth will avoid costs of 1.5–8.2 cents/kWh.

Avian Collision Mortality at 50- and 60-m Guyed Towers in Central California

Abstract. By searching for carcasses weekly year round, we estimated rates of avian fatality from collision with ten 50-m and eight 60-m temporary meteorological towers supported by guy wires near wind turbines at the Altamont Pass (n = 3) and Collinsville Montezuma Hills (n = 15) wind resource areas in central California. All towers were searched out to 55 m, beyond the farthest guy-wire anchors. Estimates for the total number of fatalities were based on searchers‘ efficiency and scavengers’ removal rates determined empirically at one of the wind farms. In 1632 searches (90.7 ± 5.4 per tower; 136.0 ± 2.8 per month), we found 85 carcasses of 19 species, for an average of 2.8 carcasses per tower per year. When adjusted for searchers‘ efficiency and scavenging, fatalities per tower per year were 6.8 ± 1.1 for all birds. Icterids, the Horned Lark (Eremophila alpestris), pipits, and sparrows accounted for 60% of carcasses, whereas night-migrating songbirds accounted for only 7% of carcasses. This level of mor...

The Hidden Factors That Make Wind Energy Cheaper than Natural Gas in the United States

Based on an analysis comparing the 580 MW Altamont Pass wind farm in California and the 22 MW Sawtooth wind farm in Idaho with natural gas-fired generation, this article finds that wind energy provides significant and quantifiable human health, wildlife, and climate change benefits not normally considered by energy planners and utility operators. These benefits make wind energy far cheaper than natural gas.

Generation innovation: Despite tricky times of late, innovations in aerodynamics, drive train and intelligent operation – should help drive the cost of wind energy back down again

THE CALIFORNIA “turbine rush” started in Altamont Pass in 1981 and ended abruptly a few years later, but not until thousands of machines filled high-wind areas of California's deserts and mountain passes.

Birds of Prey Remain at Risk

E. Kintisch's News story “Out of site” (special section on Scaling Up Alternative Energy, 13 August, p. [788][1]) discusses the bird-of-prey deaths (including golden eagles) caused by wind turbines. The story implies that the problem at the Altamont Pass Wind Resource Area (APWRA) in California

Novel Scavenger Removal Trials Increase Wind Turbine—Caused Avian Fatality Estimates

ABSTRACT For comparing impacts of bird and bat collisions with wind turbines, investigators estimate fatalities/megawatt (MW) of rated capacity/year, based on periodic carcass searches and trials used to estimate carcasses not found due to scavenger removal and searcher error. However, scavenger trials typically place ≥10 carcasses at once within small areas already supplying scavengers with carcasses deposited by wind turbines, so scavengers may be unable to process and remove all placed carcasses. To avoid scavenger swamping, which might bias fatality estimates low, we placed only 1–5 bird carcasses at a time amongst 52 wind turbines in our 249.7‐ha study area, each carcass monitored by a motion‐activated camera. Scavengers removed 50 of 63 carcasses, averaging 4.45 days to the first scavenging event. By 15 days, which corresponded with most of our search intervals, scavengers removed 0% and 67% of large‐bodied raptors placed in winter and summer, respectively, and 15% and 71% of small birds placed in winter and summer, respectively. By 15 days, scavengers removed 42% of large raptors as compared to 15% removed in conventional trials, and scavengers removed 62% of small birds as compared to 52% removed in conventional trials. Based on our methodology, we estimated mean annual fatalities caused by 21.9 MW of wind turbines in Vasco Caves Regional Preserve (within Altamont Pass Wind Resource Area, California, USA) were 13 red‐tailed hawks (Buteo jamaicensis), 12 barn owls (Tyto alba), 18 burrowing owls (Athene cunicularia), 48 total raptors, and 99 total birds. Compared to fatality rates estimated from conventional scavenger trials, our estimates were nearly 3 times higher for red‐tailed hawk and barn owl, 68% higher for all raptors, and 67% higher for all birds. We also found that deaths/gigawatt‐hour of power generation declined quickly with increasing capacity factor among wind turbines, indicating collision hazard increased with greater intermittency in turbine operations. Fatality monitoring at wind turbines might improve by using scavenger removal trials free of scavenger swamping and by relating fatality rates to power output data in addition to rated capacity (i.e., turbine size). The resulting greater precision in mortality estimates will assist wildlife managers to assess wind farm impacts and to more accurately measure the effects of mitigation measures implemented to lessen those impacts.

Map-Based Repowering and Reorganization of a Wind Resource Area to Minimize Burrowing Owl and Other Bird Fatalities

Wind turbines in the Altamont Pass Wind Resource Area (Alameda/Contra Costa Counties, California, USA) generate about 730 GWh of electricity annually, but have been killing thousands of birds each year, including

Avian and Bat Fatality Rates at Old‐Generation and Repowered Wind Turbines in California

ABSTRACT Wind turbines in the Altamont Pass Wind Resource Area (APWRA), California, USA, have caused annual fatalities of thousands of raptors and other birds. Alameda County implemented an Avian Protection Program requiring mitigation measures and eventual repowering to modern wind turbines, all intended to reduce raptor fatality rates 50% from levels estimated for 1998–2003. Two years into the 3‐year program, we compared estimates of fatality rates between 1998–2003 and 2005–2007 and between a repowered wind project (Diablo Winds) and the APWRA's old‐generation wind turbines. The APWRA‐wide fatality rates increased significantly for multiple bird species, including 85% for all raptors and 51% for all birds. Fatality rates caused by the Diablo Winds repowering project were not lower than replaced turbines, but they were 54% and 66% lower for raptors and all birds, respectively, than those of concurrently operating old‐generation turbines in 2005–2007. Because new‐generation turbines can generate nearly 3 times the energy per megawatt of rated capacity compared to the APWRA's old turbines, repowering the APWRA could reduce mean annual fatality rates by 54% for raptors and 65% for all birds, while more than doubling annual wind‐energy generation. Alternatively, the nameplate capacity of a repowered APWRA could be restricted to 209 megawatts to meet current energy generation (about 700 gigawatt‐hr), thereby reducing mean annual fatalities by 83% for raptors and 87% for all birds. In lieu of repowering, bird fatalities could be reduced by enforcing operating permits and environmental laws and by the County requiring implementation of the Alameda County Scientific Review Committee's recommendations.