Developing an efficient protocol for monitoring eagle fatalities at wind energy facilities

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.

Eagle fatalities are reduced by automated curtailment of wind turbines

“…We therefore set the density‐weighted proportion of each search area to one. This decision most likely does not affect inference because we designed our search plot dimensions such that carcass density distribution models predict >90% of the large carcasses fall within search plots (Hallingstad et al., 2018; Hull & Muir, 2010). Note that we also performed the analysis while setting the density‐weighted proportion to 0.90 and inference was the same.…”

Comparing methods to estimate the proportion of turbine-induced bird and bat mortality in the search area under a road and pad search protocol

“…We defined A(r ) as the proportion of area within 0.5 meters of r contained in R&P, which is analogous to A (r −0.5) in the notation introduced for the Cake method. After development, we shared this method with researchers who implemented the weighted distribution method in the context of estimating eagle fatalities at wind projects (Hallingstad et al 2018).…”

“…The general approach is to first estimate the number of carcasses arriving on R&P and then divide by the estimated proportion of carcasses falling on R&P,â. Ratio estimation (Thompson 2012) has also been utilized to obtainâ (Good et al 2011) by clearing vegetation from a small number of square or circular plots out to a specified distance, exhaustively searching the entire cleared areas, and calculating the proportion of the total carcasses found on R&P. A potentially more robust and less costly alternative might be to model the distribution of carcasses as a function of distance (and possibly direction) from turbines and integrate over the R&P. Such methods have been implemented by Arnett et al (2009), Huso and Dalthorp (2014), and Hallingstad et al (2018).…”

Incidental eagle carcass detection can contribute to fatality estimation at operating wind facilities

“…At the study sites with restricted search areas (due to snowfall in winter and croplands at peak growing season), the amount of viewable area and/or proportion of searchable turbines were reduced based on the length of time carcass detection was not feasible. The raptor carcass-density distribution from Hallingstad et al [10] was used to calculate the searched area adjustment in this study. The density distribution developed in Hallingstad et al [10] is based on a meta-analysis of raptor spatial data from multiple wind facilities with varying turbine designs and wind regimes.…”

“…The raptor carcass-density distribution from Hallingstad et al [10] was used to calculate the searched area adjustment in this study. The density distribution developed in Hallingstad et al [10] is based on a meta-analysis of raptor spatial data from multiple wind facilities with varying turbine designs and wind regimes.…”