Abstract
he 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 Wind Farm IV LLC. Phases I, II and III consists of 355 wind turbines that have been operating in Benton County, Indiana since 2009. Phase IV was constructed during 2015 and began commercial operation in January of 2016. A post-construction casualty study of bats was conducted by Western EcoSystems Technology, Inc. (WEST) within Phases I and III in 2009. During that study period, an Indiana bat carcass was found. The FRWF worked with the U.S. 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). FRWF contracted with WEST to complete evaluation phase monitoring of bat carcasses in 2014 and 2015 per the terms of the Habitat Conservation Plan, with the goal of determining if the level of Indiana bat mortality was within authorized limits.
The primary objective of the 2015 monitoring was to determine if the FRWF’s approved minimization measures resulted in a 50% or greater reduction in mortality compared to turbines that operated normally in 2010. The 2015 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 118 turbines from August 3 – October 14, 2015. Personnel trained in proper search techniques conducted the carcass searches. Searchers walked at a rate of approximately 45 to 60 meters (m) per minute (about 148 to 197 feet [ft] per minute) along each transect looking for bat carcasses. Transects were spaced at approximately 5 m (16 ft) intervals on road and pads, and searchers scanned the area on both sides out to approximately 2.5 m (about eight ft) for casualties as they walked each transect. Bias trials of searcher efficiency and carcass removal trials were conducted.
A total of 164 bat carcasses were found in 2015 during carcasses 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. Four big brown bats, one Seminole bat and one little brown bat were also found. No Indiana bat carcasses were found.
Bat fatality rates were calculated based on number of carcasses found, the results of bias trials, and adjustments for bats that did not fall on roads and pads. Bat fatality rates in 2015 were estimated to be 4.86 bat fatalities/MW/study period (90% confidence interval 3.66 – 6.65), which was 71.8% lower than casualty estimates at turbines operating normally in 2010. The results of monitoring during 2015 provide evidence that operational strategies exceeded the objective of reducing bat casualty rates by 50% compared to casualty estimates from turbines in normal operation modes in 2010. Within-season adjustments (for minimization strategies) were not required in 2015 because bat fatality rates were well below adaptive management thresholds.