Searcher Efficiency Research Articles

Unveiling the hidden impact: Wildlife roadkill assessment in the Paraguayan Chaco

AbstractThe incidence of wildlife roadkill significantly threatens the persistence of wildlife populations and disrupts the ecological functionality of ecosystems. This study investigates the impact of roadkills on wildlife in the Paraguayan Chaco, focusing on a 250‐km segment of Route 9 ‘Dr. Carlos Antonio López’ between Villa Hayes and Pozo Colorado. We conducted a road survey for 15 months and recorded 2338 carcasses, identifying 87 species, with mammals (41.3%), reptiles (32.3%) and birds (19.8%) being the most observed groups. The species most frequently killed included Cerdocyon thous, Caracara plancus, Thamnodynastes hypoconia and Procyon cancrivorus. We also recorded species with conservation concern. Additionally, we estimated mortality rates by accounting for sampling errors such as carcass removal and searcher efficiency, revealing annual roadkill rates of 5183 mammals, 19 402 birds and 5020 reptiles on the 250 km per year. Spatial analysis using Ripley's K statistic and HotSpot Identification highlighted significant variation in roadkill distribution across different taxonomic groups and seasons, with 51 km of road identified as hotspots when analysing all groups together. Notably, there was minimal overlap in hotspot locations between seasons and taxonomic groups, emphasizing the need for targeted mitigation strategies. Our findings challenge previous macroecological assessments suggesting low roadkill rates in Paraguay, underscoring the importance of local studies in accurately assessing ecological impacts. This study provides critical baseline data for conservation efforts and calls for further research to develop and implement effective roadkill mitigation strategies in Latin America, especially in Chaco region.

Pre-construction Risk Assessment and Post Construction On-site Surveys and Mitigation for Bird-Wind Turbine Interactions

Pre-construction risk assessment and postconstruction on-site surveys and mitigation are important components of understanding and addressing wildlife interactions with wind facilities. This presentation will cover all of these topics in detail. Pre-construction risk assessment can be a 3-phase process. Phase 1 involves preliminary site assessment, often done remotely, and is based especially on literature review. If this review suggests at-risk species may be present, then phase 2 involves verification of their presence at the site and assessment of site-specific features (topography, land cover) that may influence risk from turbines. Finally, phase 3 should involve quantitative studies to count numbers and assess potential risk. Additional surveys similar to those conducted postconstruction are also important. Post-construction surveys are typically focused on counting numbers of individuals and, more recently, estimating population-level consequences of fatalities. Counting fatalities requires surveys at and around individual wind turbines. Critical to this effort is defining the search area correctly (a small bird can fall far from turbines), accurate species identification establishing useful search intervals that vary with the size of the target species, and estimating rates of both searcher efficiency and scavenger removal. Best practices call for standardizing survey methodology across facilities to facilitate comparison and to making data public. Estimating population-level consequences of fatalities requires identifying the population of origin of affected animals, estimation of the size of the population in those origin areas, and building demographic models to estimate populationlevel consequences. Mitigation also typically follows a threestep hierarchy, with (1) avoidance; (2) minimization; and (3) compensation. Avoidance of collision is typically achieved with either macro- or micro-siting, typically underpinned by risk modeling or expert opinion. Minimization of numbers of collisions can be accomplished by detection and deterrence or operational or responsive curtailment. Compensation involves replacement of animals killed and can be achieved by habitat improvement, food supplementation, or reduction of other threats to a species. Effective replacement requires identifying the population of origin of affected animals and the factors limiting that population.

Curtailment and acoustic deterrents reduce bat mortality at wind farms

AbstractThe impacts of wind energy on bat populations is a growing concern because wind turbine blades can strike and kill bats, and wind turbine development is increasing. We tested the effectiveness of 2 management actions at 2 wind‐energy facilities for reducing bat fatalities: curtailing turbine operation when wind speeds were <5.0 m/second and combining curtailment with an acoustic bat deterrent developed by NRG Systems. We measured the effectiveness of the management actions using differences in counts of bat carcasses quantified by daily and twice‐per‐week standardized carcass searches of cleared plots below turbines, and field trials that estimated searcher efficiency and carcass persistence. We studied turbines located at 2 adjacent wind‐energy facilities in northeast Illinois, USA, during fall migration (1 Aug–15 Oct) in 2018. We estimated the effectiveness of each management action using a generalized linear mixed‐effects model with several covariates. Curtailment alone reduced overall bat mortality by 42.5% but did not reduce silver‐haired bat (Lasionycteris noctivagans) mortality. Overall bat fatality rates were 66.9% lower at curtailed turbines with acoustic deterrents compared to turbines that operated at manufacturer cut‐in speed. Curtailment and the deterrent reduced bat mortality to varying degrees between species, ranging from 58.1% for eastern red bats (Lasiurus borealis) to 94.4 for big brown bats (Eptesicus fuscus). Hoary (Lasiurus cinereus) and silver‐haired bat mortality was reduced by 71.4% and 71.6%, respectively. Our study lacked a deterrent‐only treatment group because of the expense of acoustic deterrents. We estimated the additional reduction in mortality with concurrent deployment of the acoustic deterrent and curtailment under the assumption that curtailment and the acoustic deterrent would have reduced mortality by the same percentage at adjacent wind‐energy facilities. Acoustic deterrents resulted in 31.6%, 17.4%, and 66.7% additional reductions of bat mortality compared to curtailment alone for eastern red bat, hoary bat, and silver‐haired bat, respectively. The effectiveness of acoustic deterrents for reducing bat mortality at turbines with rotor‐swept area diameters >110 m is unknown because high frequency sound attenuates quickly, which reduces coverage of rotor‐swept areas. Management actions should consider species differences in the ability of curtailment and deterrents to reduce bat mortality and increase energy production.

A stochastic simulation model for assessing the masking effects of road noise for wildlife, outdoor recreation, and bioacoustic monitoring

Traffic noise is one of the leading causes of reductions in animal abundances near roads. Acoustic masking of conspecific signals and adventitious cues is one mechanism that likely causes animals to abandon loud areas. However, masking effects can be difficult to document in situ and the effects of infrequent noise events may be impractical to study. Here, we present the Soundscapes model, a stochastic individual-based model that dynamically models the listening areas of animals searching for acoustic resources (“searchers"). The model also studies the masking effects of noise for human detections of the searchers. The model is set in a landscape adjacent to a road. Noise produced by vehicles traveling on that road is represented by calibrated spectra that vary with speed. Noise propagation is implemented using ISO-9613 procedures. We present demonstration simulations that quantify declines in searcher efficiency and human detection of searchers at relatively low traffic volumes, fewer than 50 vehicles per hour. Traffic noise is pervasive, and the Soundscapes model offers an extensible tool to study the effects of noise on bioacoustics monitoring, point-count surveys, the restorative value of natural soundscapes, and auditory performance in an ecological context.

Factors affecting searcher efficiency and scavenger removal of bat carcasses in Neotropical wind facilities

AbstractBat fatalities at wind facilities have been reported worldwide, and environmental impact assessments depend on searches for carcasses around wind turbines to quantify impacts. Some of the carcasses may go undetected by search teams or be removed by scavengers during search intervals, so these biases must be evaluated and taken into account in fatality estimation. We investigated the influence of different factors on searcher efficiency and scavenger removal in a dry forest area in northeastern Brazil, one of the regions with the highest density of wind turbines in the Neotropics. We conducted searcher efficiency and scavenger removal trials around 34 wind turbines from January 2017 to January 2018. Searcher efficiency was influenced by cover type, season, and carcass size, ranging between 12% for small bats in shrub vegetation during the rainy season and 96% for large bats in absent or sparse vegetation during the dry season. Carcass type and season affected scavenger removal; carcass persistence time was shorter for chicks (1.2 days) than for bats and mice (2.1 days), and the probability of a carcass persisting for a whole day was higher in the rainy season, while the probability of carcass persistence for 7, 14, and 28 days was higher in the dry season. The scavenger community was composed of canids, birds of prey, and insects, with systematic removal of carcasses by the crab‐eating fox (Cerdocyon thous) throughout the year and by dung beetles in the rainy season. Based on our findings, impact assessments of wind facilities on bats should conduct searcher efficiency trials in all seasons and cover types around wind turbines, using bat carcasses or models of different sizes. Scavenger removal trials should cover all seasons as well, and use mouse carcasses (but not chick carcasses) as surrogates for bats.

Ecological and methodological drivers of persistence and detection of bird fatalities at power lines: Insights from multi-project monitoring data

Environmental impact assessment (EIA) follow-up monitoring in energy projects, such as wind farms, solar facilities and power lines, frequently encompasses bird fatality surveys based on regular carcass searches. Since a large number of bird carcasses are often not found, field experiments to determine carcasses persistence (CP) and searcher efficiency (SE) biases in fatality surveys are typically performed for every single project. These data are, however, rarely used beyond the scope of each original project. We compiled data from CP and SE trials performed under 36 independent monitoring programs aiming to assess bird mortality at transmission lines in Portugal, whose results were until now unavailable or dispersed in grey literature. We used survival analysis and generalized linear mixed-effects models to investigate the ecological and methodological factors influencing CP times and SE rates. Bird carcass size was a key driving factor of both CP times and SE rates of human observers, which were consistently out-performed by scent detection dogs. Season and habitat interactions had also an important role in CP patterns, while variations in SE rates by human observers were largely influenced by ground visibility (i.e., a combination of ground cover and vegetation height). Our results reinforce previous studies indicating that CP and SE biases are site-specific and determined by a wide range of ecological and methodological factors not always accounted in standard trial designs. Overall, our study demonstrates that data routinely collected under bird monitoring programs from multiple projects can be combined to identify broad ecological patterns, limitations of current studies and, ultimately, improve EIA follow-up practice.

Estimating bat fatality at a Texas wind energy facility: implications transcending the United States–Mexico border

AbstractWind energy development causes bat fatalities. Despite emphasis on understanding and reducing these impacts, few data are available for the southwest region of the United States and northern Mexico. We monitored bat fatalities for a full year (March 2017–March 2018) at a wind energy facility in south Texas near the United States–Mexico border. We established search plots of 100-m radius at eight randomly selected turbines (of 255) and searched the roads and pads at an additional 92 turbines. We conducted weekly searches from spring through fall and bimonthly during winter. We used GenEst (Generalized Mortality Estimator) to estimate bat fatalities corrected for searcher efficiency, carcass removal, and density-weighted proportion of area searched. We found 205 bats during standardized searches, the majority of which were Brazilian free-tailed bats (Tadarida brasiliensis, 76%). The corrected fatality estimates were 16 bats/megawatt/year (95% confidence interval [CI]: 12 – 30 bats/megawatt/year) across all species. Species composition at our site is similar to that of northern Mexico, an area of expanding wind energy development with no published studies.

The need to consider searcher efficiency and carcass persistence in railway wildlife fatality studies

To improve mitigation planning on railways, it is crucial to accurately assess the number of fatalities resulting from this type of infrastructure. To illustrate the relevance of considering the two main errors from the sampling process (searcher efficiency and carcass persistence), we corrected the estimation of mammal fatalities (> 1 kg) on a 750-km railway located in the Brazilian Savanna accounting for these errors. Observed fatalities were collected by two observers in a rail inspection vehicle (RV). We estimated searcher efficiency comparing the number of carcasses found during the searcher efficiency trials on foot and by RV on the same subsections of the railway. Carcass persistence was estimated based on trials with a subset of carcasses that had their persistence verified over three consecutive days. Searcher efficiency was 29.8% and daily carcass persistence probability was 99.7%. Nine surveys on the entire railway (2015–2016) recorded 1950 carcasses and, after correcting for the sampling errors, we estimated that 4286 mammals died on this railway in 23 months. This estimate is 2.2 times larger than the observed number of fatalities. These errors should not be neglected, as our results demonstrate that the number of observed carcasses is a misperception in relation to the true number of fatalities caused by the railway. However, our results also indicate that dealing with these errors in railway ecology is still a challenge. We stress the need to test more suitable sampling designs for fatality estimates on railways.

Wildlife and infrastructure: impact of wind turbines on bats in the Black Sea coast region

In Eastern Europe, wind energy production is currently promoted as an important source of renewable energy, yet in most cases without appropriate consideration of the negative impacts wind turbines (WT) may have on protected species such as bats. Here, we present first data on fatality rates, fatality factors and the likely origin of bats killed by WT in the Dobrogea region (Romania), located in a major migratory corridor for wildlife in Eastern Europe. Over a 4-year period, we found a total of 166 bat carcasses from 10 species, mostly representing migratory species such as Pipistrellus nathusii and Nyctalus noctula. Most fatalities at WT occurred in July and August. We documented 15 cases of barotrauma and 34 cases of blunt-force trauma in carcasses found below WT. After adjusting for carcass removals and variations in searcher efficiency, we estimated for the 4-year study period a total of 2394 bat casualties at the studied WT facility consisting of 20 units, resulting in a mean fatality rate of 30 bats/WT/year, or 14.2 bats/MW/year. By implementing a curtailment measure at wind speeds below 6.5 m/s, we reduced fatality rates by 78%. Isoscape origin models based on hydrogen stable isotope ratios in fur keratin revealed that the majority of N. noctula that were killed by WT or captured nearby in mist nets originated from distant areas in the North (Ukraine, Belarus, Russia). The estimated high fatalitjegangy rates of bats at WT in this area have far-reaching consequences, particularly for populations of migratory bats, if no appropriate mitigation schemes are practised.

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

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.

Bat mortality due to wind turbines in Canada

Wind turbines have been hypothesized to affect bat populations; however, no comprehensive analysis of bat mortality from the operation of wind turbines in Canada has been conducted. We used data from carcass searches for 64 wind farms, incorporating correction factors for scavenger removal, searcher efficiency, and carcasses that fell beyond the area searched to estimate bat collision mortality associated with wind turbines in Canada. On average, 15.5 ± 3.8 (95% CI) bats were killed per turbine per year at these sites (range = 0−103 bats/turbine/yr at individual wind farms). Based on 4,019 installed turbines (the no. installed in Canada by Dec 2013), an estimated 47,400 bats (95% CI = 32,100−62,700) are killed by wind turbines each year in Canada. Installed wind capacity is growing rapidly in Canada, and is predicted to increase approximately 3.5-fold over the next 15 years, which could lead to direct mortality of approximately 166,000 bats/year. Long-distance migratory bat species (e.g., hoary bat [Lasiurus cinereus], silver-haired bat [Lasionycteris noctivagans], eastern red bat [Lasiurus borealis]) accounted for 73% of all mortalities. These species are subject to additional mortality risks when they migrate into the United States. The little brown myotis (Myotis lucifugus), which was listed as Endangered in 2014 under the Species At Risk Act (SARA), accounted for 13% of all mortalities from wind turbines, with most of the mortality (87%) occurring in Ontario. Population-level impacts may become an issue for some bat species as numbers of turbines increase. © 2016 The Wildlife Society.

Searcher efficiency and survey coverage affect precision of fatality estimates

Studies at renewable energy sites often attempt to estimate avian and bat fatalities or fatality rates (e.g., fatalities/megawatt [MW]/year). However, searcher efficiency and level of survey effort among sites are variable. We evaluated how searcher efficiency and proportion of area surveyed affected precision of fatality estimates and probability of detecting rare fatalities (e.g., fatalities of an endangered species). We measured searcher-efficiency rates of human and dog-handler teams for 3 fatality types: feather spots, small carcasses, and large carcasses. We also created high and low searcher-efficiency scenarios to evaluate effects of searcher efficiency across a broader range. Model selection on a set of logistic regression models for our empirical trials supported search team and fatality type as important predictors of searcher-efficiency rates, and demonstrated that dog-handler teams had higher searcher efficiency for all fatality types than human search teams. We used model simulations to evaluate fatality estimates obtained across the 4 searcher-efficiency scenarios and 10 levels of survey coverage: 10–100%, in increments of 10%. At each level of survey coverage, width of confidence intervals decreased as searcher efficiency increased; however, as survey coverage increased, width of the confidence intervals stabilized, and further increases in coverage did not lead to increases in precision. Average fatality estimates were biased positively and this bias increased with lesser searcher efficiency. The survey coverage necessary to achieve 80% detection probability for rare fatalities (defined as 1, 5, or 15 fatalities) decreased as searcher efficiency increased for all fatality types. When a rare fatality was defined as a single fatality out of 1,000, an 80% detection probability was achieved only by dog-handler teams and the high searcher-efficiency scenario, and only for large carcasses. Our results emphasize the need for managers and agencies to consider study objectives and site characteristics when selecting level of survey coverage, type of search team, and other options to maximize searcher efficiency. © 2016 The Wildlife Society.

Impact of Wind Facilities on Bats in the Neotropics

We monitored the bat fatalities caused by a 13 turbines wind facility installed in western Puerto Rico (West Indies) over a period of 23 months. The post-construction monitoring includes observed fatalities and a corrected fatality estimate expressed as bats/ turbine/year adjusted for bat carcass removal rates, searcher efficiency, and percent area searched. Data on seasonality of fatalities and distance of carcasses from turbines is also provided. Eleven out of the 13 species of bats in Puerto Rico suffered fatalities, including all five species of phyllostomids. These were: Molossus molossus and Tadarida brasiliensis (Molossidae); Artibeus jamaicensis, Monophyllus redmani, Stenoderma rufum, Brachyphylla cavernarum and Erophylla bombifrons (Phyllostomidae); Noctilio leporinus (Noctilionidae); Eptesicus fuscus and Lasiurus minor (Vespertilionidae); and Mormoops blainvillei (Mormoopidae). This is one of the first published reports of the impact of wind turbines on bats in the Neotropics.

Mortality estimation from carcass searches using the R‐package carcass — a tutorial

This article is a tutorial for the R‐packagecarcass. It starts with a short overview of common methods used to estimate mortality based on carcass searches. Then, it guides step by step through a simple example. First, the proportion of animals that fall into the search area is estimated. Second, carcass persistence time is estimated based on experimental data. Third, searcher efficiency is estimated. Fourth, these three estimated parameters are combined to obtain the probability that an animal killed is found by an observer. Finally, this probability is used together with the observed number of carcasses found to obtain an estimate for the total number of killed animals together with a credible interval.

Estimates and correlates of bird and bat mortality at small wind turbine sites

Small wind turbines (SWTs) are an increasingly popular means to generate renewable energy worldwide. Flexibility in size and design allow SWTs to be installed in a much wider range of settings compared to large wind turbines. While large wind turbines can cause substantial mortality of birds and bats, the extent and correlates of such collision mortality at SWTs have not been quantified. Thus, siting decisions for SWTs are currently made with considerable uncertainty of their impact on wildlife. We combined field data and questionnaire surveys of SWT owners to assess the range and correlates of bird and bat mortality at SWT sites (mean hub height 10.2 m [range 4.0–26.4 m], mean rotor diameter 4.0 m [range 0.9–15.0 m], for both free-standing and building mounted turbines). During 171 carcass searches at 21 UK SWT sites we did not find any collision casualties. Thirty-one (14.6 %) of 212 SWT owners reported bird casualties of at least 12 species groups and 3 (1.4 %) reported bat casualties (unidentified species). Based on the questionnaire returns and using a model that accounts for detectability of casualties (through variation in visit frequency, searcher efficiency and average levels of scavenger removal) we estimated that between 0.079 and 0.278 birds, and between 0.008 and 0.169 bats may be killed turbine−1 year−1, equating to 1,567–5,510 birds and 161–3,363 bats year−1 in the UK based on recent estimates of numbers of units installed. Sites with higher levels of bird activity tended to be more likely to report bird casualties. Systematically derived likely ranges of mortality as provided here are urgently needed to inform future SWT planning policy.

Empirical Evidence for Factors Affecting Searcher Efficiency and Scavenging Rates at a Coastal, Terrestrial Wind-Power Facility

Abstract The rapid expansion of wind power development in recent years has accentuated the need to develop standard guidelines for identifying, assessing, and monitoring potential impacts to birds and bats. Although postconstruction mortality estimates generally take into account well-established sources of bias, including searcher efficiency and scavenging loss, methods for addressing these biases can be improved. Currently used bias-adjustment methods differ across studies, do not explicitly account for factors that may affect initial bias estimates, and often use averaged or assumed levels of bias. We examined scavenging and detection trial data from a 3-y study at a small, terrestrial wind-farm in coastal New Jersey. Logistic regression models indicated that carcass size, substrate, and observer all affected carcass detection rates, with larger carcasses more likely to be detected than smaller carcasses, and those located on bare ground or grass more likely to be detected than those on gravel. Known-fate mark–recapture models indicated that scavenging rates were highest within the first 3 d of placement, with some variation among seasons. We suggest that empirically based estimates of factors affecting observer detection and scavenging loss be generated for individual wind-farm mortality studies, because they likely vary across sites and could heavily bias resulting adjustment factors and mortality estimates.

Hidden Markov models for estimating animal mortality from anthropogenic hazards

Carcass searches are a common method for studying the risk of anthropogenic hazards to wildlife, including nontarget poisoning and collisions with anthropogenic structures. Typically, numbers of carcasses found must be corrected for scavenging rates and imperfect detection. Parameters for these processes (scavenging and detection) are often estimated using carcass distribution trials in which researchers place carcasses in the field at known times and locations. In this manuscript I develop a variety of estimators based on multi-event or hidden Markov models for use under different experimental conditions. I apply the estimators to two case studies of avian mortality, one from pesticide exposure and another at wind turbines. The proposed framework for mortality estimation points to a unified framework for estimation of scavenging rates and searcher efficiency in a single trial and also allows estimation based only on accidental kills, obviating the need for carcass distribution trials. Results of the case studies show wide variation in the performance of different estimators, but even wider confidence intervals around estimates of the numbers of animals killed, which are the direct result of small sample size in the carcass distribution trials employed. These results also highlight the importance of a well-formed hypothesis about the temporal nature of mortality at the focal hazard under study.

Wind turbine fatalities approach a level of concern in a raptor population

Mortality from collisions with increasing numbers of wind turbines is a potential hazard to raptor populations, but the actual effects on a population scale have rarely been studied based on field data. We estimated annual collision numbers for Red Kites Milvus milvus in the German federal state of Brandenburg (29,483km2). A hierarchical model considering carcass persistence rate, searcher efficiency and the probability that a killed animal falls into a searched area was applied to results of carcass searches at 617 turbines. Collision risk varied significantly with season. The model estimated 308 (95% CrI 159–488) Red Kite fatalities at 3044 turbines operating during 2012, representing 3.1% of the estimated post-breeding population of 9972 individuals. Using the potential biological removal (PBR) method, mortality thresholds of 4.0% were obtained for migratory Red Kite populations. This level of mortality may be reached when turbine numbers increase within a few years. Since wind turbine collisions may affect Red Kites throughout the global range, a more detailed assessment of the actual impacts on populations is needed, especially because the PBR does not account for the predominance of adult birds among the collision victims.

A new stochastic dynamic tool to improve the accuracy of mortality estimates for bats killed at wind farms

Although generally considered environmentally friendly, wind power has been associated with extensive mortality of birds and bats. In this perspective, there is a need for reliable estimates of fatalities at wind farms, where the heterogeneity of the basic information, used among environmental assessment studies, is unlikely to support an accurate universal estimation method. We tested the applicability of the Stochastic Dynamic Methodology (StDM) to estimate bat fatalities, based on multifactorial cause–effect relationships (by integrating multi-model inference statistical analysis and dynamic modelling) between mortality estimates, detected fatalities and the selected key-components of the reality, such as the real number of bat mortalities simulated, the rate of carcasses removal, the searcher efficiency, the monitoring periodicity and the number of turbines for different realistic scenarios associated with particular wind farm conditions. Although some existing mortality estimators are considered accurate, the choice of a given universal formula for all mortality assessments, based on deterministic parameters and assumptions, may originate unsuspected errors. Therefore, we propose a flexible dynamic modelling framework, the StDM estimator, where the obtained algorithms are adaptable to the universe of application intended. The StDM estimator takes into account random, non-constant and scenario dependent parameters, providing bias-corrected estimates. The StDM estimator was applied for the European wind farm context and validated in the most cases tested, through the confrontation with independent data. Overall, this approach is considered a valuable tool to improve the quality of mortality estimates at onshore wind facilities, within the local, environmental and methodological gradients (including the cases where no mortality is detected), namely in the scope of environmental impact assessments and general ecological monitoring programmes.

Estimation of bird and bat mortality at wind‐power farms with superpopulation models

Summary Collision of birds and bats with turbines in utility‐scale wind farms is an increasing cause of concern. Carcass counts conducted to quantify the ‘take’ of protected species need to be corrected for carcass persistence probability (removal by scavengers and decay) and detection probability (searcher efficiency). These probabilities may vary with time since death, because of intrinsic changes in carcass properties with age and of heterogeneity (preferential removal of easy‐to‐detect carcasses). In this article, we describe the use of superpopulation capture–recapture models to perform the required corrections to the raw count data. We review how to make such models age specific and how to combine trial experiments with carcass searches in order to accommodate the fact that carcasses are stationary (which affects the detection process). We derive information about optimal sampling design (proportion of the turbines to sample, number of sampling occasions, interval between sampling occasions) and use simulations to illustrate the expected precision of mortality estimates. We analyse data from a small wind farm in New Jersey, in which we find the estimated number of fatalities to be twice the number of carcasses found. Synthesis and applications. Our approach to estimation of wind farm mortality based on data from carcass surveys is flexible and can accommodate a range of different sampling designs and biological hypotheses. Resulting mortality estimates can be used (1) to quantify the required amount of compensation actions, (2) to inform mortality projections for proposed wind development sites and (3) to inform decisions about management of existing wind farms.