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

Abstract

Risk of birds colliding with wind turbines, especially protected species like bald eagle and golden eagle, is a fundamental wildlife challenge the wind industry faces when developing and operating projects. The U.S. Fish and Wildlife Service requires wind facilities that obtain eagle take permits to document permit compliance through eagle fatality monitoring. If trained Operations and Maintenance (O&M) staff can reliably detect and report carcasses during their normal routines, then their ‘incidental detections’ could contribute substantially to meeting monitoring requirements required by eagle take permits. The primary objective of this study was to quantify incidental detection of eagle carcasses by O&M staff under a variety of landscape contexts and environmental conditions throughout 1 year. We used the incidental detection probabilities (proportion of decoys detected by O&M staff), along with raptor carcass persistence data and area adjustments, to calculate overall probability of incidental detection (i.e., incidental g). We used feathered turkey decoys as eagle-carcass surrogates for monthly detection trials at 6 study sites throughout the U.S. We evaluated the primary drivers of incidental detection using logit regression models including season, viewshed complexity, and a derived variable called the “density quartile” as covariates. We used an Evidence of Absence-based approach to estimate the overall probability of incidental detection. Detection probabilities decreased as viewshed complexity increased and as distance from the turbine increased. The resulting overall probability of incidental detection for the 12-month period ranged from 0.07 to 0.47 (mean = 0.31). The primary drivers of variability in incidental g were detection probability and the area adjustment. Results of our research show that O&M staff were capable of incidentally detecting trial carcasses while performing their typical duties. Incorporating incidental detection by O&M staff in eagle fatality monitoring efforts is a reliable means of improving estimates of a facility’s direct impacts on eagles.