Estimating wind turbine fatalities using integrated detection trials

Abstract

Fatality monitoring at wind projects requires carcass detection trials to adjust fatality estimates for the proportion of fatalities not found. However, detection trials vary greatly in metric, duration, carcass monitoring schedule, species, number placed, state of decomposition, whether placed within or outside search areas, and other factors. We introduce a new approach for estimating fatalities by quantifying overall detection rates rather than separate rates for searcher detection error and carcass persistence, and by leaving placed and found fatality carcasses undisturbed throughout monitoring. We placed 2 fresh‐frozen bird carcasses weekly at random sites within fatality search areas and on randomized days Monday–Friday at Sand Hill and Santa Clara wind projects, Altamont Pass Wind Resource Area, California, USA. To estimate detection rates, we used logit regression to fit detection outcomes on body mass, which served as an axis of similitude between placed trial carcasses and fatality finds. Adjusted carcass placement rates among species detected by searchers regressed on true placement rates with a slope of 1.0 so long as sufficient numbers of trial carcasses were placed, thus validating our approach as an unbiased estimator. Our approach generally estimated lower fatality rates than did conventional approaches, the latter of which demonstrated biases in searcher detection rates and carcass persistence rates whether based on proportion of carcasses remaining or mean days to removal. Our approach also revealed detection errors that highlight the difficulty of finding and identifying the remains of dead animals, and which warrant routine reporting. Despite averaging only a 5‐day search interval on intensively grazed annual grasslands where ground visibility was usually high, our experienced fatality monitors averaged 4.3 searches/first carcass detection, failed to detect 25% of 75 species represented by placed carcasses, and misidentified carcasses to species among 44% of species detected. Estimates of time since death also suffered bias and large error. Our approach more realistically simulates carcass detection probabilities associated with fatality monitoring, is less costly, facilitates hypothesis testing, eliminates multiple sources of error and bias suspected of conventional methods, and enables quantification of errors in estimated time since death, species identifications, and false negative findings. © 2018 The Wildlife Society.

Effects of Wind Turbine Curtailment on Bird and Bat Fatalities

“…In study 2, we performed 3 BACI experiments at the Sand Hill project, which involved human searches for fatalities at an average of 5‐day intervals between searches at 151 Sand Hill turbines monitored from April 2012 through March 2015 (Smallwood et al 2018). Besides undergoing project‐wide shutdowns for 15 weeks each winter to mitigate raptor fatalities, mechanical and circuit failures at all but 16% of these old turbines resulted in frequent forced shutdowns lasting up to the 1,086‐day duration of our study.…”

“…We left found carcasses in place for possible repeat discovery. We also tested the dog team by randomly placing fresh‐frozen and thawed bird and bat carcasses within search areas, where we marked 88 bird carcasses by clipping flight feathers and 95 bat carcasses by removing 1 foot (Smallwood et al 2018). Use of animal carcasses was authorized under permits from the United States Fish and Wildlife Service (MB135520‐0) and the California Department of Fish and Wildlife (SC‐00737).…”

“…Use of animal carcasses was authorized under permits from the United States Fish and Wildlife Service (MB135520‐0) and the California Department of Fish and Wildlife (SC‐00737). Placed carcasses served as fatality detection trials used to adjust fatality finds for the proportion of fatalities not detected (Smallwood 2017, Smallwood et al 2018). Fatality searchers were blind to the trials, and reported trial carcasses in the same manner as turbine‐caused fatalities, except that searchers also reported whether carcasses had been marked.…”

“…Furthermore, finding zero fatalities might mean that none occurred or that fatalities occurred but none were found. Compared to measuring experimental treatment effects applied to animals the size of griffon vultures, measuring a treatment effect for small birds and bats is made even more difficult by low fatality detection rates owing to quick scavenger removal (Smallwood et al 2010) and low searcher detection of available carcasses (Smallwood 2017, Smallwood et al 2018). Fortunately, shorter search intervals (Smallwood et al 2018) and use of scent‐detection dogs (Arnett 2006, Mathews et al 2013) have improved fatality detection.…”

“…Study 1 used scent‐detection dogs at Buena Vista and Golden Hills Wind Energy Projects (K. S. Smallwood, independent researcher, unpublished data). Study 2 used human searchers averaging 5‐day intervals between searches at Sand Hill Energy Project (Smallwood et al 2018). Our first objective was to test whether wind turbine curtailment, and conversely, conversion of wind turbines from inoperable to operable, affected fatality rates of birds and bats.…”