Altamont Pass Wind Resource Area 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.

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.

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

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.

Influence of Behavior on Bird Mortality in Wind Energy Developments

ABSTRACT As wind power generation is rapidly expanding worldwide, there is a need to understand whether and how preconstruction surveys can be used to predict impacts and to place turbines to minimize impacts to birds. Wind turbines in the 165‐km2 Altamont Pass Wind Resource Area (APWRA), California, USA, cause thousands of bird fatalities annually, including hundreds of raptors. To test whether avian fatality rates related to rates of utilization and specific behaviors within the APWRA, from March 1998 to April 2000 we performed 1,959 30‐minute behavior observation sessions (360° visual scans using binoculars) among 28 nonoverlapping plots varying from 23 ha to 165 ha in area and including 10–67 turbines per plot, totaling 1,165 turbines. Activity levels were highly seasonal and species specific. Only 1% of perch time was on towers of operating turbines, but 22% was on towers of turbines broken, missing, or not operating. Of those species that most often flew through the rotor zone, fatality rates were high for some (e.g., 0.357 deaths/megawatt of rated capacity [MW]/yr for red‐tailed hawk [Buteo jamaicensis] and 0.522 deaths/MW/yr for American kestrel [Falco sparverius]) and low for others (e.g., 0.060 deaths/MW/yr for common raven [Corvus corax] and 0.012 deaths/MW/yr for turkey vulture [Cathartes aura]), indicating specific behaviors or visual acuity differentiated these species by susceptibility to collision. Fatality rates did not correlate with utilization rates measured among wind turbine rows or plots for any species except burrowing owl (Athene cunicularia) and mallard (Anas platyrhynchos). However, mean monthly fatality rates of red‐tailed hawks increased with mean monthly utilization rates (r2 = 0.67) and especially with mean monthly flights through turbine rows (r2 = 0.92). Fatality rates increased linearly with rates of utilization (r2 = 0.99) and flights near rotor zones (r2 = 1.00) for large raptor species and with rates of perching (r2 = 0.13) and close flights (r2 = 0.77) for small non‐raptor species. Fatalities could be minimized or reduced by shutting down turbines during ≥1 season or in very strong winds or by leaving sufficiently large areas within a wind farm free of wind turbines to enable safer foraging and travel by birds.

Bird Mortality in the Altamont Pass Wind Resource Area, California

Abstract The 165‐km2 Altamont Pass Wind Resource Area (APWRA) in west‐central California includes 5,400 wind turbines, each rated to generate between 40 kW and 400 kW of electric power, or 580 MW total. Many birds residing or passing through the area are killed by collisions with these wind turbines. We searched for bird carcasses within 50 m of 4,074 wind turbines for periods ranging from 6 months to 4.5 years. Using mortality estimates adjusted for searcher detection and scavenger removal rates, we estimated the annual wind turbine–caused bird fatalities to number 67 (80% CI = 25–109) golden eagles (Aquila chrysaetos), 188 (80% CI = 116–259) red‐tailed hawks (Buteo jamaicensis), 348 (80% CI = −49 to 749) American kestrels (Falco sparverius), 440 (80% CI = −133 to 1,013) burrowing owls (Athene cunicularia hypugaea), 1,127 (80% CI = −23 to 2,277) raptors, and 2,710 (80% CI = −6,100 to 11,520) birds. Adjusted mortality estimates were most sensitive to scavenger removal rate, which relates to the amount of time between fatality searches. New on‐site studies of scavenger removal rates might warrant revising mortality estimates for some small‐bodied bird species, although we cannot predict how the mortality estimates would change. Given the magnitude of our mortality estimates, regulatory agencies and the public should decide whether to enforce laws intended to protect species killed by APWRA wind turbines, and given the imprecision of our estimates, directed research is needed of sources of error and bias for use in studies of bird collisions wherever wind farms are developed. Precision of mortality estimates could be improved by deploying technology to remotely detect collisions and by making wind turbine power output data available to researchers so that the number of fatalities can be related directly to the actual power output of the wind turbine since the last fatality search.

Burrowing Owl Mortality in the Altamont Pass Wind Resource Area

Abstract: We estimated wind turbines in the Altamont Pass Wind Resource Area (APWRA), California, USA, kill >100 burrowing owls (Athene cunicularia hypugaea) annually, or about the same number likely nesting in the APWRA. Turbine‐caused mortality was up to 12 times greater in areas of rodent control, where flights close to the rotor plane were disproportionately more common and fatalities twice as frequent as expected. Mortality was highest during January through March. Burrowing owls flew within 50 m of turbines about 10 times longer than expected, and they flew close to wind turbines disproportionately longer within the sparsest turbine fields, by turbines on tubular towers, at the edges of gaps in the turbine row, in canyons, and at lower elevations. They perched, flew close to operating turbine blades, and collided disproportionately more often at turbines with the most cattle dung within 20 m, with the highest densities of ground squirrel (Spermophilus beecheyi) burrow systems within 15 m, and with burrowing owl burrows located within 90 m of turbines. A model of relative collision threat predicted 29% of the 4,074 turbines in our sample to be more dangerous, and these killed 71% of the burrowing owls in our sample. This model can help select the most dangerous turbines for shutdown or relocation. All turbines in the APWRA could be shut down and blades locked during winter, when 35% of the burrowing owls were killed but only 14% of the annual electricity was generated. Terminating rodent control and installing flight diverters at the ends of turbine rows might also reduce burrowing owl mortality, as might replacing turbines with new‐generation turbines mounted on taller towers.

The effects of wind turbines on antipredator behavior in California ground squirrels ( Spermophilus beecheyi)

Electricity-generating wind turbines are an attractive energy source because they are renewable and produce no emissions. However, they have at least two potentially damaging ecological effects. Their rotating blades are hazardous to raptors which occasionally fly into them. And wind turbines are very noisy when active, a feature that may interfere with the lives of animals beneath them. We studied California ground squirrels ( Spermophilus beecheyi) in the Altamont Pass Wind Resource Area of Northern California. These squirrels emit vocalizations that alert others to the presence of a predator, and so may be forced to compensate for turbine noise by modifying antipredator behavior. We compared the antipredator behavior of squirrels at two sites, one close to and the other far from turbines, and under two conditions, during baseline and playback of conspecific alarm calls. We generated composite two variables using principle components analysis, one representing vigilance and one representing another cautionary antipredator tactic, for further statistical comparisons. Animals at the Turbine site exhibited elevated levels of vigilance and showed increased caution demonstrated in part, by returning to the area near their burrows during alarm calling. We conclude that this site difference is probably caused by the disparity in turbine noise, since predator abundance, group size, and vegetation type and density were similar for the two sites. Though population level impacts of these behavioral differences remain to be explored, our results indicate that behavioral impacts of turbines on wildlife should be considered during future turbine development.

BEHAVIOR OF RED-TAILED HAWKS IN A WIND TURBINE DEVELOPMENT

Birds flying within windfarms can be killed when they collide with wind turbines. Raptors, especially red-tailed hawks (Buteo jamaicensis), are more susceptible to collisions than other birds, which may be attributable to their specific foraging and flight behavior. To more fully understand the problem, and to reduce raptor mortality, it is necessary to acquire more information on habitat use and flight behavior by raptors inhabiting windfarms. Between June 1999 and June 2000, we watched raptors for 346 hours in the Altamont Pass Wind Resource Area, the largest windfarm in North America. We recorded flight behavior in relation to characteristics of the topography such as slope aspect, elevation, and inclination and in relation to various weather variables including wind speed and wind direction. We found that red-tailed hawk behavior and their use of slope aspect differed according to wind speed. Hawks perched more often in weak winds than in strong. Red-tailed hawks were more likely to soar during low wind conditions and kite during strong wind, particularly on hillsides that faced into the wind as opposed to hillsides shielded from the wind. This is likely a result of their use of deflection updrafts for lift during flight. During our study, when winds were strong and from the south–southwest, kiting behavior occurred on south–southwestern facing slopes with inclines of greater than 20% and peak elevations greater than adjacent slopes. Accordingly, mitigation measures to decrease red-tailed hawk fatalities should be directed specifically to these areas and others fitting this general model. Wind farm managers can power down turbines at the top of these hazardous slopes when they pose the greatest danger—when winds are strong and facing perpendicularly to the slope.