Abstract
Researchers typically conduct fatality monitoring to determine a wind energy facility’s direct impacts on wildlife. In the United States, wind energy impacts on eagles have received increased attention in recent years because eagle incidental take permits became available. Permit holders are required to conduct fatality monitoring to evaluate compliance with permitted eagle take. Our objective was to develop an efficient eagle fatality monitoring protocol with a quantifiable detection probability based on a stationary scanning search method. We conducted scanning searches for eagle carcasses at four wind energy facilities. We estimated searcher efficiency of the scanning search method using feathered turkey decoys as eagle carcass surrogates, used publicly available data on large raptor carcass distances from turbines to evaluate the proportion of carcasses expected to occur in searched areas, and estimated carcass persistence rates for game birds and raptors. These three bias adjustments were combined to estimate the overall probability of detection for the scanning search method. We found generally high searcher efficiency for the scanning search method, with 76% of decoys detected; however, detection decreased with distance and difficulty of visibility class. Mean carcass persistence time varied between 28 and 76 days for raptors and between three and nine days for game birds, showing that game birds do not persist as long as raptors. We estimated that 95% of large avian carcasses fall within 100 m of turbine bases, and 99% fall within 150 m. Using these estimates and assuming a 30-day search interval for all facility turbines, we estimated that the probability of detecting a large raptor carcass using the scanning search method at a wind facility ranged from 0.50 to 0.69. Our research suggests a monitoring program that uses scanning searches can be a cost-effective approach for gathering data necessary to meet incidental eagle take permit requirements.
Highlights
Growing concerns over climate change and carbon emissions have prompted state and national governments to prioritize the development of wind energy resources
Our objectives were to: 1) estimate searcher efficiency using the scanning search method, 2) estimate the proportion of eagle carcasses occurring within our search areas using existing data on large raptor fatalities, 3) estimate carcass persistence probability of raptors and compare it to game bird persistence, 4) use searcher efficiency, raptor carcass density distribution, and raptor carcass persistence probability to estimate an overall probability of detection, and 5) demonstrate how the overall probability of detection from the scanning search method can be used to develop take estimates for compliance assessment
Logistic regression models of decoy detection (Tables 4 and 5) indicated that at both Juniper Canyon (JC) in 2013 and Big Horn I (BH I)/Big Horn II (BH II) in 2014, searchers detected decoys consistently with respect to distance in the easy visibility class and decoy detection remained above 50% out to 100 m in the moderate visibility class (Fig 5)
Summary
Growing concerns over climate change and carbon emissions have prompted state and national governments to prioritize the development of wind energy resources. Global wind energy production has been continuously increasing during the past 25 years, with an average of 25% growth each year and a world-wide total of 487 gigawatts (GW) of operating wind capacity in 2016 [1]. An increase in wind capacity of 69 GW is projected world-wide for 2018 and 2019 [3]. Wind energy is considered a “green” energy source, but concerns exist over risks to wildlife from wind facilities [4,5,6,7]. The impacts of wind facilities on bald (Haliaeetus leucocephalus) and golden (Aquila chrysaetos) eagles have received attention in the USA; both species are susceptible to collisions with wind turbines [8, 9]. While data from the US Fish and Wildlife Service (USFWS) suggest that shooting, poisoning, starvation, and electrocutions are the primary sources of mortality for golden eagles [10], vulnerability to sources of mortality is known to vary geographically [8, 11]
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