Abstract
Consumers Energy Company (Consumers) operates the Crescent Wind Project (Crescent) in Hillsdale County, Michigan. Crescent began operating in February 2021, and consists of 60 wind turbines with a total generating capacity of 166 megawatts. Consumers subsequently obtained a US Fish and Wildlife Service recovery (research) permit to test the effectiveness of an acousticactivated (smart) curtailment system for Indiana bats (Myotis sodalis) and northern long-eared bats (M. septentrionalis), as well as other bat species, from May 15 to October 15, 2021. The research permit provided take coverage for the federally endangered Indiana bat and threatened northern long-eared bat that might occur as part of this study.
The main goal of this study was to investigate ways to minimize impacts to Indiana and northern long-eared bats from wind operations. To this end, 20 turbines each were assigned to one of three treatments: a control operating at a manufacturer’s cut-in speed of 3.0 meters per second (m/s), blanket curtailment with a nightly raised cut-in speed of 5.0 m/s, or smart curtailment with a nightly raised cut-in speed of 5.0 m/s only when bat calls were detected. The research project aimed to answering the following questions: What are the percent reductions in fatality achieved with blanket curtailment below 5.0 m/s and smart curtailment below 5.0 m/s compared to turbines operating at manufacturer’s cut-in speed (3.0 m/s)? Can a similar level of minimization be obtained through smart curtailment and blanket curtailment?
All turbines were searched twice a week from May 20 to October 15, 2021, for a total of 2,473 carcass searches. Thirty cleared plots (10 in each of three treatment groups) were searched out to 80 meters by detection dog teams, and roads and pads of the remaining 30 turbines were searched out to 100 meters by human searchers. In total, 1,699 bat carcasses were discovered during the searches. The most frequently detected species were the big brown bat (38%), eastern red bat (23%), hoary bat (20%), and silver-haired bat (19%). Searchers also found four Seminole bats, two evening bats, and one little brown bat.
Using GenEst, a generalized estimator of fatality, the estimated fatality rates by treatment were 85.00 bats/turbine/study period (90% confidence interval [CI]: 72.66–101.19) for the control group, 49.41 (90% CI: 41.91–59.41) for the blanket curtailment group, and 46.69 (90% CI: 38.84– 56.32) for the smart curtailment group. Overall, curtailment reduced bat fatalities at Crescent by approximately 42 to 45%, and there was no statistical difference in fatality rates between the blanket and smart curtailment treatments. Fatality rates were higher in fall than in summer, and curtailment appeared to be somewhat more effective in the summer than the fall. No Indiana bats or northern long-eared bats were found, and the mean fatality estimate for both species was zero based on the Evidence of Absence estimator.