Final Report Bird and Bat Fatality Studies Fowler Ridge I Wind-Energy Facility Benton County, Indiana: April 6 - October 30, 2009


Title: Final Report Bird and Bat Fatality Studies Fowler Ridge I Wind-Energy Facility Benton County, Indiana: April 6 - October 30, 2009
Publication Date:
April 12, 2010
Pages: 62
Sponsoring Organization:

Document Access

Attachment: Access File
(2 MB)


Johnson, G.; Ritzert, M.; Nomani, Sarif; Bay, Kim (2010). Final Report Bird and Bat Fatality Studies Fowler Ridge I Wind-Energy Facility Benton County, Indiana: April 6 - October 30, 2009. Report by Western Ecosystems Technology Inc (WEST). pp 62.

BP Wind Energy North America, Inc. (BPWENA) is developing a wind-energy facility in five separate phases for a total build out capacity of 1,000 megawatts (MW) in Benton County, Indiana. Currently, the first three phases have a total energy capacity of 750 MW. The first phase of the facility, Fowler Ridge I, is jointly owned by BPWENA and Dominion Energy, Inc. and has a nameplate capacity of 301 MW.  The Fowler Ridge I Wind–Energy Facility (FRWEF-I) is located approximately 0.5 miles (0.8 km) south and east of Fowler, Indiana, and consists of 122 Vestas V82 1.65-MW turbines and 40 Clipper C96 2.5-MW turbines. BPWENA contracted Western Ecosystems Technology, Inc. (WEST) to conduct a post-construction fatality monitoring study at the Fowler Ridge I facility.  The study was designed to assess the level of impacts to birds and bats (i.e., high, moderate, low) relative to other regional projects from operation of the wind-energy facility.  Because not all turbines were sampled and because all study plots were not completely cleared of crops, the study was not designed to quantify mortality with a high degree of accuracy for the entire wind energy facility, nor was it designed to detect every wind turbine casualty present on the site.  Monitoring at the Fowler Ridge I facility occurred from April 6 to October 30, 2009.


FRWEF-I is located in western Indiana in Benton County. The topography of the site is mostly flat to slightly rolling and there are no hills, ridges, or other areas of starkly elevated topography. Habitat within and surrounding the FRWEF-I is dominated by tilled agriculture, with corn and soybeans being the dominant crops. Of the roughly 29,000 acres (about 43 mi2) within the FRWEF-I and half-mile (0.8-km) buffer, row crops compose 93%, developed areas compose 5.7%, pastures/hayfields compose 1.7%, grasslands compose 0.1%, and forested areas compose 0.4% of the land cover.  
The monitoring study for the FRWEF-I consisted of the following components: 1) standardized carcass surveys of selected turbines within a square plot centered on the turbine; 2) searcher efficiency trials to estimate the percentage of carcasses found by searchers; 3) carcass removal trials to estimate the length of time that carcasses remain in the field for possible detection; and 4) adjusted fatality estimates based on the results of searcher efficiency trials and carcass removal trials and proportion of the plot searched.


Twenty-five wind turbines were included in the study, and nine of those had crops cleared in late summer within the search plot to facilitate conducting surveys in mature corn and soybean fields. To the extent possible, turbines were selected for sampling using a systematic design with a random start so that the search effort was spread throughout the entire wind-energy facility. However, some modifications to turbine sample selection had to be made to accommodate landowners who did not wish to participate in the study. Square plots 160 by 160 meters (525 by 525 feet) in size were established around the 25 turbines and systematically searched for carcasses. Standardized carcass surveys were conducted anywhere from twice a week to twice a month, with more intensive surveys conducted during the spring and fall migration periods.  


Searcher efficiency trials were conducted in the same areas as carcass surveys and searcher efficiency was estimated by the type of carcass (bird or bat), size of carcass (bird carcasses only) and season. Estimates of searcher efficiency were used to adjust the total number of carcasses found for those missed by searchers, correcting for detection bias. Carcass removal studies were conducted during each season, outside of the carcass search plots (i.e., near turbines that were not included in the standard search plots). Estimates of carcass removal were used to adjust the total number of carcasses found for those removed from the study plots, correcting for removal bias. 


A total of 778 turbine searches were conducted over the course of the fatality monitoring study. Twenty-eight birds and 156 bats were found during standardized carcass surveys or incidentally. Twenty-four birds comprised of 11 identified species were found during scheduled searches, and four additional bird fatalities were found incidentally. The most common bird species found as a casualty at the site was killdeer (four fatalities), followed by tree swallow (three), red-tailed hawk (three) and unidentified large bird (three); two unidentified ducks were also found as fatalities.  The three unidentified large birds and two unidentified ducks found during the study consisted entirely of a few large bones with no feathers or flesh remaining. The ducks were identified to type based on skull characteristics, but no skulls were found associated with the remaining three unidentified large birds.  The FRWEF-I is near an area designated as an Important Bird Area (IBA) due to high concentrations of staging American golden plovers during spring migration. Although concerns have been raised over the potential for collision mortality, no American golden plover fatalities were found during this study.


Of all the bird fatalities, 35.6% were found within 30 m (99 feet) of the turbine, 28.5% were found from 31 to 60 m (100 to 197 feet), and 35.7% were found more than 60 m from the turbine. Most (64.2%) of the bird fatalities occurred during fall migration (September 3 to October 29), 25.0% occurred during spring migration (April 6 to May 25), and 10.7% occurred during the breeding season (June 10 to August 14). 


A total of 107 bat fatalities comprised of six species were found during scheduled searches, and an additional 49 bats were found incidentally. Most (94.2%) of the bat fatalities were migratory tree bats, including 56 eastern red bats (35.9%), 48 hoary bats (30.8%), 42 silver-haired bats (26.9%) and one unidentified Lasiurus spp. (either hoary or eastern red bat). The other bat fatalities included four big brown bats, three little brown bats, one northern long-eared bat, and one Indiana bat.  The Indiana bat is listed as an endangered species by the US Fish and Wildlife Service. The Indiana bat casualty was collected as an incidental casualty on September 11, 2009. The majority (88.2%) of bat fatalities were found within 40 m (131 feet) of the turbines, and most (73.7%) of the bat fatalities occurred from August 1 to September 15, with an additional 12.8% found between September 16 and October 30. 


A total of 89 carcasses (17 large birds, 12 small birds, and 60 bats) were placed in the field during searcher efficiency trials conducted on 11 separate dates. Observer detection rates were 64.3% for large birds, 37.5% for small birds, and 56.0% for bats. A total of 82 carcasses were placed in study area throughout the duration of the monitoring period for carcass removal trials, including 16 large birds, 12 small birds, and 54 bats. By day ten, approximately 30% of the bats remained, while approximately 20% of the large birds and nearly 35% of the small birds remained.  Seven turbines surveyed during the study season were lit with Federal Aviation Administration (FAA) mandated aviation strobe lights and 18 were unlit. There were no significant differences in the number of bird or bat fatalities occurring at turbines with or without FAA lighting. 


The estimated fatality rate and 90% confidence interval (CI) for the entire study period (all three study seasons) was 5.26 birds/turbine (90% CI = 3.52, 10.25) and 15.03 bats/turbine (10.89, 20.52). Given the 301-MW nameplate capacity of the FRWEF-I, the overall fatality estimate for the entire study period (all three study seasons) was 2.83 bird fatalities/MW and 8.09 bat fatalities/MW. 
The estimated bird fatality rate of 2.83 birds/MW is lower than average compared to other wind-energy facilities in the Midwest. Overall bird fatality estimates at seven Midwest wind-energy facilities located in Nebraska, Wisconsin, Minnesota, Iowa and Illinois have ranged from 0.6 to 7.2 and averaged 4.28 birds/MW/year. The estimated bat fatality rate of 8.09 bats/MW would be considered moderate when compared to other wind-energy facilities in North America, and is somewhat below average based on the regional average for reported bat fatality estimates at seven wind energy facilities in the Midwest, where bat fatality estimates ranged from 0.8 to 30.6, and averaged 9.8 bats/MW/year. 


Species composition of bat fatalities was similar to that at most other wind-energy facilities, in that the majority (94.2%) of identified bat fatalities was comprised of three species of migratory tree bats, namely the hoary, eastern red and silver-haired bat. These three species typically comprise over 75% of bat fatalities at wind-energy facilities throughout North America. Based on the timing of fatalities for these three species and the lack of forest cover that might provide habitat for resident bats, most of the fatalities were apparently migrants through the area, as is the case at virtually all other wind energy facilities in North America. It seems unlikely that the FRWEF-I is located along a concentrated tree bat migration route, as there are no topographical features or large expanses of forested areas that would tend to concentrate migrating bats. 


Pre-construction ground-based bat acoustical surveys were conducted at the Fowler Ridge Wind Resource Area from August 15 – October 19, 2007 and from July 17 – October 15, 2008, time periods that cover the time frame during which most bat mortality at wind energy facilities occurs throughout North America.  Overall bat detections were low to moderate for sites in the Midwest, ranging from 4.7 bat calls/detector-night in 2007 to 6.45 bat calls/detector-night in 2008.  Although only 3.2% of the bat casualties found at the FRWEF-I in 2009 were high-frequency species (i.e., Myotis spp.), high-frequency bats comprised 49.0% of bat calls in 2007 and 34.2% of bat calls recorded in 2008, suggesting that high frequency species such as Myotis bats may be much less susceptible to turbine collisions.


The discovery of an Indiana bat turbine casualty at a wind-energy facility sited in a corn and soybean agroecosystem was unexpected. To our knowledge, this is the first Indiana bat related casualty documented at a wind-energy facility in North America, as well as the first documented casualty of a federally-listed bat species at a wind-energy facility. The Indiana bat casualty found during this study is also apparently the first record of Indiana bat in Benton County, Indiana. Based on the lack of Indiana bat summer habitat at or near the FRWEF-I, and the time frame that he Indiana bat casualty occurred (estimated to be September 9, 2009), this individual was likely a migrant through the area. 


To date there have been fewer than 10 studies conducted to estimate bird and bat fatalities from wind turbine operations in the Midwest, and studies at the Fowler Ridge Wind Energy Facility represent the first such studies in Indiana.   Results of this study further contribute to our understanding of wind-energy impacts to birds and bats. As more wind-energy facilities are built in the region, and additional studies become available, a clearer picture of the impacts to birds and bats will emerge.

Find Tethys on InstagramFind Tethys on FacebookFind Tethys on Twitter
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.