The Fowler Ridge Wind Farm (FRWF) collectively includes Fowler Ridge Wind Farm LLC, Fowler Ridge II Wind Farm LLC, Fowler Ridge III Wind Farm LLC, and Fowler Ridge IV Wind Farm LLC. The FRWF consists of 420 wind turbines in four phases in Benton County, Indiana. A post-construction casualty study of bats was conducted by Western EcoSystems Technology, Inc. (WEST) within Phases I and III in 2009, during which an Indiana bat carcass was found. The FRWF worked with the US Fish and Wildlife Service and developed a Habitat Conservation Plan for the Indiana bat designed to minimize Indiana bat casualties. FRWF received an Incidental Take Permit for Indiana bats in August of 2014 (TE95012A-0). Monitoring the effectiveness of minimization measures is required by both the Habitat Conservation Plan and the Incidental Take Permit. Two years of more intensive evaluation phase monitoring, utilizing a larger sample of turbines to test effectiveness of applied minimization procedures, was completed for FRWF Phases I, II and III in 2014 and 2015. Because Indiana bat mortality was below adaptive management thresholds, less intensive implementation phase monitoring was applied for FRWF Phases I, II and III in 2016 and 2017, and will continue unless adaptive management thresholds are exceeded in the future. The second year of evaluation phase monitoring, requiring a minimum of 33% of turbines to be searched, was completed at FRWF Phase IV in 2017.
The 2017 casualty study occurred during the fall (August 1 – October 15) migration period for Indiana bats. Casualty searches were completed once per week on roads and gravel pads of 140 turbines from August 1 – October 11, 2017. Personnel trained in proper search techniques conducted the carcass searches. Searcher efficiency and carcass persistence trials were conducted to adjust for removal bias and searcher efficiency.
A total of 130 bat carcasses were found in 2017 during carcass searches and incidentally. Similar to previous years of monitoring, the most commonly found bat species were eastern red bats, silver-haired bats, and hoary bats. Eight big brown bats, one Seminole bat and one evening bat (state-listed as endangered) were also found. No Indiana bat, northern long-eared bat or any other Myotis spp. carcasses were found.
Bat casualty rates were calculated based on the number of carcasses found, the results of bias trials, and adjustments for bats that did not fall on roads and pads. Bat casualty rates in 2017 were estimated to be 5.24 bat casualties/MW/study period (90% confidence interval: 4.09 – 6.90), which was 66.3% lower than casualty estimates at turbines operating normally in 2010. The results of monitoring during 2017 provide evidence that operational strategies exceeded the objective of reducing bat casualty rates by 50%, compared to casualty estimates from turbines operating normally in 2010. Within-season adjustments of minimization strategies were not required in 2017 because bat casualty rates were well below adaptive management thresholds.