Nicholas School of the Environment and Earth Sciences
Bat Site Assessments
Bat Fatalities: West Virginia
There have been several contentious battles during the past few years concerning the impacts large scale wind-turbines have on bat species. Wind associated wind mortalities gained notoriety from cases in West Virginia and Pennsylvania that have killed hundreds of bats (Blum, 2005).
The Mountaineer Wind Energy Center on Backbone Mountain in West Virginia opened in 2002 as the largest wind farm east of the Mississippi with an output of 66 MW. The 44 (1.5 MW) turbines are 328 feet high, and include a rotor diameter of 231 feet (FPL, 2007). In 2004 a PhD student at the University of Maryland began noticing dead bats on the site and estimated the 2004 death toll between 1,500 and 4,000 bats. The bats found at the sites included hoary bats, red bats, and eastern pipistrelle bats. None of the bats are listed as endangered species under the Endangered Species Act of 1973 (Blum, 2007). The bat deaths may have been caused by the increase in open spaces around the turbines since the forest needed to be cut back in order for construction of the turbines. The results of the 2004 report are discussed below.
2004 Bat Conservation International Study
Edward Arnett and othe researchers completed a comprehensive study about the impacts on bats in Pennsylvania and West Virginia. The report, “Relationships between Bats and Wind Turbines in Pennsylvania and West Virginia” studied the Mountaineer Wind Energy Center in West Virginia, and Meryersdale Wind Energy Center in Pennsylvania daily to accurately estimate bat fatality.
The team studied the relationship between bat fatalities and weather conditions, wind turbine speed, and FAA lights on turbines between July 31 and September 13, 2004. The areas around half of the wind turbines were searched daily, while the other half were searched weekly. Trained dogs were used to detect dead bats and thermal imaging cameras were used to assess bat, bird and insect activity from August 2-27, 2004 at the Mountaineer site in West Virginia.
During the six-week period, 398 bats were found dead at the Mountaineer site and 262 at the Meyersdale, Pennsylvania wind farm. The group noted intriguing patterns of fatalities, including discovering more dead adult male bats than juveniles or females. Fatalities were distributed across all turbines, except one which was not in operation during the study. More bats than average were found at turbines near an end or the center of the turbine string.
The study showed no correlation between fatalities and the use of FAA lights on the turbines even though insect activity increased near FAA lights. Weather conditions did seem to play a significant role in the bat fatalities at both sites however. The majority of bats were killed on low wind nights. On those nights, there was still enough wind to keep the turbines in operation at a speed of 17 rotations per minute. The team observed that fatalities tended to increase just before and after the passage of storm fronts.
The ten-day thermal imaging assessment made a total of 2,398 observations, including bats (998, 41%), insects (503. 20%), birds (37, 1%) and unknowns (860, 35%). Bats proved to be most active within two hours of sunset, and their activity around the turbines was sporadic, ranging from 9 bats to 291 passing the turbines per night. Ultimately, bat activity was strongly correlated to activity of insects. The bats also exhibited interesting interactions with the blades of the turbines. Bats were observed chasing turbine blades, and attempting to land on stationary blades, with the authors of the report suggesting bat curiosity with moving and non-moving objects.
Although research about bat fatalities due to wind farms is still in its infancy, the research done by Edward Arnett and his team provide valuable information that can help create measures to prevent future bat fatalties at wind farms.
Ongoing Research(Arnett et al, 2006)
In 2005, a five-year study began in south-central Pennsylvania at the site of a proposed wind farm. The study is being conducted by the Bats and Wind Energy Cooperative with help from the American Wind Energy Assiociation, Bat Conservation Internation, the National Renewable Energy Laboratory and the U.S. Fish and Wildlife Service, all of whom comprise the Bats and Wind Energy Cooperative. Edward Arnett is spearheading the study again. The project's goal is to determine the level and patterns of bat activities prior to wind turbine construction, and attempt to correlate bat activity with weather and other environmental variables. The study will provide baseline data to determine if pre-construction bat activity can be used to predict bat fatalities post-construction. The proposed wind farm is located on a forested ridge and a reclaimed ridge that was previously strip-mined.
In 2006, the group released an annual report updating their study. During the first year, echolocation calls for bats were detected one half-hour before sunset and one half-hour after sunrise each day from August 1, 2005 until November 1, 2005. Bat activity was variable but generally highest from mid-August through mid-September. Bats were most active immediately after sunset, and their activity decline through the night until before sunrise the next morning. Activity also increased as the temperature increased, until 19-21 degrees Celsius, at which activity began to decline. The first year of sampling also showed that bat activity decreased 11-39% with each 1 meter/second increase in wind speed.
See some results from both of Arnett's studies here.