Criterion Power Partners, LCC, (CPP) completed construction and initiated operation of the Criterion Wind Project in Garrett County, Maryland in 2010. The project includes 28, 2.5 megawatt wind turbine generators for a total generating capacity of 70 MW. Beginning in April 2011, Criterion initiated the first year of post-construction monitoring surveys to estimate the impacts of project operations on bird and bat species. The second year of post-construction monitoring was conducted beginning in April 2012 and followed the protocol designated as part of the Habitat Conservation Plan (HCP) prepared for the project in application for an Incidental Take Permit.
The primary objectives of the 2012 monitoring study was to determine (1) the level of bird and bat mortality attributable to collisions with wind turbines for the entire facility for the study period, and (2) determine the effectiveness of turbine operational adjustments implemented as part of the project HCP. The monitoring study consisted of four components: 1) standardized carcass surveys of project turbines; 2) searcher efficiency trials to estimate the percentage of carcasses found by searchers; 3) carcass removal trials to estimate the length of time that a carcass remained in the field for possible detection; and 4) adjusted fatality estimates for bird and bat species calculated by correcting survey results for potential biases (e.g., area searched, searcher efficiency, carcass removal).
The monitoring study period was from April 1 to November 15, 2012. Search plots were established around 14 turbines (50%) in the project and the carcass search schedule was for weekly searches at the selected turbines, weather and safety permitting. Search plots varied in shape and size due to habitat constraints, but in most cases areas up to approximately 40-50 m (~130-165 ft) from the turbines were cleared of vegetation for access and construction purposes and this area was used as the search plot. Parallel transects were spaced and delineated approximately 5 m (~16 ft) apart within the search plot and surveyors systematically walked the transects while scanning the ground for fatalities or injured birds or bats.
During the study, 28 birds representing 12 species and 82 bats representing five species were found either during standardized carcass searches or incidentally during the study period. The most commonly found bird species were red-eyed vireo and golden-crowned kinglet, while eastern red bat and hoary bat accounted for the majority of the bat fatalities found. Bird and bat fatalities were spread throughout the entire survey period and throughout the entire project with the number of fatalities peaking for both birds and bats in the fall.
A total of 275 bird carcasses and 200 bat carcasses were placed for searcher efficiency trials over the study period. Searcher efficiency was estimated for the first half of the study period (April 5 to July 15 – labeled the spring) and the second half (July 16-November 15 – labeled the fall) to investigate potential changes over time. For small birds searcher efficiency was 0.75 in spring and 0.48 in fall, for large birds was 1.00 in both spring and fall, and for bats was 0.65 in spring and 0.49 in fall. A total of 489 carcasses were placed for carcass removal trials. For small birds, mean carcass removal was 7.17 days in the spring and 5.37 days in the fall. For large birds, mean carcass removal was 5.77 days in the spring and 4.31 days. For bats, mean carcass removal was 6.70 days in the spring and 4.59 days in the fall.
For small birds, the probability that a carcass would remain in the search plot and be found by a searcher was 0.50 in the spring and 0.29 in the fall. For large birds, the probability that a carcass would remain in the search plot and be found was 0.54 in the spring and 0.46 in the fall. For bats, the probability that a carcass would remain in the search plot and be found was 0.43 in the spring and 0.26 in the fall.
Fatality estimates were adjusted based on the corrections for carcass removal, observer detection bias, and the area searched to account for carcasses potentially falling outside the plot. Combining both spring and fall estimates, the overall adjusted estimate for small birds was 4.19 small birds per turbine for the study period or 1.68 small birds per MW. For large birds the overall adjusted fatality estimate was 1.28 large birds per turbine for the study period or 0.51 large birds per MW. The fatality estimate for all birds combined was 5.47 birds per turbine or 2.19 birds per MW for the study period. For bats the overall estimate fatality estimate was 19.50 bats per turbine for the study period or 7.80 bats per MW.
During the period from July 15 to October 15, the Project implemented turbine operation adjustment to minimize the impacts to bats from the turbines. Specifically, the turbine blades were feathered when wind speeds were 5.0 meters per second or below to minimize the rotor speed to approximately 2 rotations per minute (RPM) or less. This measure is part of the conservation plan that CPP has committed to in the Project HCP. The overall bat mortality measured during the study was 19.50 bats per turbine. The bat mortality rate in 2011 for a similar study period was 39.03 bats per turbine. The turbine operation constraints in 2012 resulted in approximately a 51% reduction in bat mortality. To further investigate the effects of the turbine operations, the study results were analyzed for the period when the adjustments were in place, nights of July 15 through October 15 for both 2011 and 2012. Bat mortality for the period from July 15 to October 15 for 2011 and 2012 was 29.16 bats per turbine and 11.38 bats per turbine respectively. During this period the turbine adjustments resulted in approximately a 62% reduction in bat mortality.