Abstract
The Hopkins Ridge Wind Project is located in the rolling hills south and west of the Tucannon River and northeast of Dayton, Columbia Count y, Washington. Phase I of the wind project consists of 83 Vestas 1.8 MW turbines with a total nameplate capacity of approximately 150 MW. Due to concern over potential impacts from the wind project development, Puget Sound Energy with the assistance of a Technical Advisory Committee developed a post-construction study plan to monitor impacts to birds and bats over a minimum of two years. The first year of monitoring surveys were conducted on the site between January and December 2006.
The primary objective of the monitoring study is to estimate the number of avian and bat casualties attributable to collisions with wind turbines and meteorological towers for the entire project on an annual basis. The monitoring study consists of four components: (1) standardized carcass searches of selected turbines or turbine strings to measure observed casualty rates; (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 remains in the field for possible detection; and (4) a Wildlife Incident Reporting and Handling System for wind project personnel to handle and report casualties found in the project area incidentally to the study.
Carcass searching surveys took place at 41 turbines and two permanent met towers. Search plots were 180 meters on a side (90 meter radius from the tower turbine) and centered on the turbine. Surveyors walked parallel transects within the search plot spaced approximately 6-12 meter apart while scanning the ground for fatalities or injured birds or bats. Standardize searches of all selected turbines and the met to wers (43 plots) were conducted once every four week (28 day) period. During the spring and fall migration periods, a sub-set of 22 of the selected turbines were searched once a week.
A total of 865 plot searches were conducted over the one year monitoring study period (January- December 2006). Thirty-eight bird fatalities comprised of 17 identified species and two unidentified species were found and 19 bat fatalities comprised of four species and one unidentified bat were found. Bird fatalities were found near 25 different turbines; bat fatalities were found near 14 different turbines. The average distance of bird casual ties to the nearest turbine was 45 meters; the average distance of bat casualties to the nearest turbine was 26 meters. No bird or bat carcasses were found that were attributed to the met towers.
Passerines comprised 60% and upland gamebirds comprised 18% of the avian fatalities. Ring-necked pheasant and European starling, two introduced species, were the most common bird fatalities with seven (18%) each. Horned lark was the most common native species with six (15%) fatalities. Including the unknown passerines as possible migrants, approximately 61% of the passerines were considered resident and 39% were likely migrants; 26% of all avian fatalities found were considered nocturnal migrants. Three species of raptors, American kestrel (3), northern harrier (1) and Cooper's hawk (1) were found. No Federal or State Threatened or Endangered species were found during the study. Fatality rate was highest in the winter (37%), followed by the spring (26%), summer (21%) and fall (16%). No increase in fatalities was observed during the spring and fall migration seasons. There was no strong concentration of avian fatalities within the search plots. One turbine (T59) had four fatalities and three turbines (T17, T28, T74) had three fatalities. Most turbine searches produced no fatalities.
Bat fatalities were found between April 28 and October 26, 2006. Thirteen (68%) of the bat fatalities occurred during the months of August or September, which is considered the fall migration season for bats. Five (26%) occurred during the spring and one fatality was found in July. Silver-haired bat comprised 63% and hoary bat 21% of the bat fatalities. One little brown bat, one big brown bat, and one unidentified bat made up the remainder of the bat fatalities. There did not appear to be any strong concentrations of bat fatalities within the search plots.
Overall fatality estimates were calculated by adjusting for carcass removal and observer detection bias. The estimated number of all bird fatalities per turbine per year was 2.21 and the lower and upper 90% confidence limits around this estimate were 1.64 and 2.92. The estimated number of small bird fatalities per turbine per year with 90% confidence limits was 1.45 (0.93, 21.4) and large bird fatalities per turbine per year was 0.76 (0.42, 1.17). European starling and ring-necked pheasant were the most commonly observed fatalities with an estimated fatality rate of 0.37 per turbine per year. Excluding starlings (a non-protected species) and ring-necked pheasant (an introduced non-native species), the overall estimate and 90% confidence limits are approximately 1.47 (0.98, 2.02) bird fatalities per turbine per year. Ten fatalities were found which were considered nocturnal migrants; the estimated number of nocturnal migrant fatalities per turbine per year was 0.82 (0.38, 1.44).
Adjustments for carcass removal and observer detection bias for bats were made using the estimates for small birds. The estimated number of bat fatalities per turbine per year and associated 90% confidence limits was 1.13 (0.69, 1.71).
Fatality estimates for birds and bats from the study are similar to other wind projects in the region. All fatalities found were assumed to be wind project related so the estimate of avian mortality is an over-estimate of actual wind project mortality. In order to compare Hopkins Ridge to other wind projects with different turbines, the fatality rates were standardized on a per MW capacity basis. For Hopkins Ridge the estimate was 1.23 birds per MW per year. This estimate was lower than the nearby Combine Hills (2.56 bird fatalities per MW) and Stateline (2.90 fatalities per MW) projects, and the overall average for new generation wind projects in the U.S of 3.1 fatalities per MW. The Hopkins Ridge bat fatality rate of 0.63 per MW capacity per year is also lower than Combine Hills (1.88 per MW) and Stateline, (1.70 per MW), and the average rate for new generation wind projects in the west and mid-west of 2.10 per MW.
Species composition for bird and bat fatalities was similar to composition at other wind projects in the Pacific Northwest with horned lark making up the majority of the native avian fatalities and silver-haired bat the majority of bat fatalities. When grouped together, upland gamebirds were also common fatalities. The raptor fatality rate was slightly higher than other regional wind projects and similar to what would be predicted based on pre-project estimated use defined as the number of raptors observed per 20-minute survey. The estimated fatality rate for nocturnal migrants fell within the range of other wind projects studied in the Pacific Northwest. No difference in fatality rate was found between lit and un-lit turbines.