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Evaluating Bird and Bat Post-Construction Impacts at the Sheffield Wind Facility, Vermont

The Sheffield Wind Energy facility, a 40 megawatt project that went into service in October 2011, released the first season of bird/bat mortality. Total bird fatality estimates for the project site for the entire season was 211 (95% CI: 147, 321), with an estimated 13.17 birds killed per turbine (95% CI: 9.20, 20.05). A total of 87 bats of three species from 1 April-31 October, all of which were migratory tree-roosting bats. Bat carcasses were found at all 16 turbines. The full report can be found by clicking on the links at the bottom of this page.

EXECUTIVE SUMMARY

Wind energy is the fastest growing energy sector in the world. Although it is generally considered to be an "environmental friendly" source of energy, high numbers of bat and bird fatalities have been documented at wind facilities in both North America and Europe, with especially high fatalities in forested eastern U.S. The objectives of this study are to estimate the total number of fatalities of bird and bat species at a wind facility in Vermont and to determine effectiveness and cost of raising cut-in speed of turbines (i.e., curtailment) to decrease bat fatalities. This project is located at the Sheffield Wind Facility in Caledonia County near Sheffield, Vermont (herein referred to as the "project site").

We initiated a post-construction and operational mitigation study in spring 2012. We conducted daily fatality searches at eight of the 16 available turbines for the post-construction study from 1 April-2 June and 1-31 October 2012 (herein referred to as "Period 1" and "Period 3", respectively) and conducted surveys at all 16 turbines for the operational mitigation study from 3 June-30 September 2012 (herein referred to as "Period 2"). We estimated bird and bat fatality using the U.S. Geological Survey's Fatality Estimator software (Data Series 729). We found a total of 35 birds of 12 species from 1 April-31 October. Bird carcasses were found at 13 of the 16 turbines. A total of 34 birds were used in bias trials. Overall searcher efficiency was estimated to be 45%, with 100% (95% confidence interval [CI]: 100, 100), 38% (95% CI: 21, 56), and 33% (95% CI: 19, 47), for Easy, Moderate, and Difficult/Very Difficult visibility classes, respectively. Carcass persistence was estimated to be 12.51 days (95% CI: 5.26, 32.73).

Total bird fatality estimates for the project site for the entire season was 211 (95% CI: 147, 321), with an estimated 13.17 birds killed per turbine (95% CI: 9.20, 20.05) and 5.27 per MW (95% CI: 3.68, 8.02). The operational mitigation study was conducted during Period 2, at which time half of the turbines at the project site were curtailed. As such, the bird fatality estimates for the project site are actual fatalities observed rather than estimates of fatalities had the wind facility been fully-operational during the summer and fall season. As a result, it is possible that the estimated bird fatalities during Period 2 are lower than would have occurred otherwise.

We found a total of 87 bats of three species from 1 April-31 October, all of which were migratory tree-roosting bats; no cave-roosting species were found during the study. Hoary bat (Lasiurus cinereus) consisted of 54% of the bat carcasses found, while eastern red bat (Lasiurus borealis) and silver-haired bat (Lasionycteris noctivagans) made up 30% and 16%, respectively. Bat carcasses were found at all 16 turbines. A total of 73 bat carcasses from the project site were used in searcher efficiency trials. Overall searcher efficiency was estimated to be 48%, with 100% (95% CI: 100, 100), 43% (95% CI: 25, 61), and 37% (95% CI: 23, 54), for Easy, Moderate, and Difficult/Very Difficult visibility classes, respectively. Sixty-one fresh bats were used in the carcass persistence trials, which was estimated to be 6.92 days (95% CI: 4.85, 10.53). Total bat fatality estimates for the project site for the entire season was 235 (95% CI: 160, 361), with an estimated 14.65 bats killed per turbine (95% CI: 10.06, 22.56) and 5.86 per MW (95% CI: 4.02, 9.02). The operational mitigation study was conducted during Period 2, at which time half of the turbines at the project site were curtailed. As such, the bat fatality estimates for the project site are actual fatalities observed rather than estimates of fatalities had the wind facility been fully-operational during the summer and fall season. As a result, it is possible that the estimated bat fatalities during Period 2 are lower than would have occurred otherwise.

The operational mitigation study was conducted for a total of 120 nights from 3 June-30 September. There were two turbine treatments: 1) fully operational (i.e., cut-in speed at 4.0 m/s) and 2) cut-in speed at 6.0 m/s. Each of the 16 turbines was randomly assigned to one of the two treatments, with each treatment having eight replicates on each night of the study. Treatments were balanced every eight nights to achieve a balanced assignment of treatments over the entire study period, for a total of 60 nights of treatment for each turbine. Treatments were implemented from half an hour before sunset to sunrise during periods when the ambient air temperature was greater than 9.5°C (49°F) and wind speeds were less than 6.0 m/s. We found that operational mitigation had a statistically significant effect on bat fatalities. An average of 1.0 (95% CI: 0.6, 1.8) fresh bats per turbine were found at turbines following operational mitigation compared to 2.7 (95% CI: 1.9, 3.9) fresh bats per turbine found at turbines following full operation, resulting in an estimated 60% (95% CI: 29, 79) decrease in bat fatalities.

A second field season will be conducted at the project site from 1 April-31 October 2013. An annual report for the 2013 field season will be available 15 January 2014 and a final project report will be available 15 December 2014.

Sheffield_wind_2012_annual_report_final_3-25-2013_thumb
Sheffield Wind 2012 Annual Report Final 3 25 2013

Download file (4.22 MB) pdf


Source: http://www.vce.org/Sheffiel...

MAR 25 2013
http://www.windaction.org/posts/36806-evaluating-bird-and-bat-post-construction-impacts-at-the-sheffield-wind-facility-vermont
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