WHITE PAPER THE USE OF HABITAT CORRIDORS TO GUIDE MIGRATING BATS SAFLY PAST WIND FARMS
Josephine Lock Nose No Limit, Zionsville, Indiana [email protected]
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1 Executive Summary
Biologists investigating the impact on birds of wind energy generation in the late 1990’s were surprised when they also began finding the carcasses of bats beneath the turbines. During the twenty years since, hundreds of studies have been conducted to determine the severity of this problem, to better understand the reasons it occurs, and to find viable solutions that reduce its impact on bat populations.
While it remains unclear how many bats lose their lives this way, research suggests that the numbers could easily be as high as a million bats a year in the United States alone.
The reasons for this loss of life are still not fully understood, but what the research clearly shows is that tree roosting migratory species are among those most affected, that most casualties occur during the bats’ fall migration, and that bats are deliberately changing course to approach the turbines.
There are many hypotheses regarding what attracts the bats and motivates them to fly so close to the rotating blades. Most of these theories surmise the bats equate the characteristics of the turbines with those of tall trees and approach with the expectation of accessing resources such as food, a mate, or a place to roost. However, it is likely that the motivations vary for different species or even for individual bats.
In the Midwest region, the species most frequently found beneath turbines include the eastern red bat (Lasiurus bo- realis), the big brown bat (Eptesicus fuscus), the silver-haired bat (Lasionycteris noctivagans), and the hoary bat (La- siurus cinereus). None of these species are listed as endangered or threatened, but their population sizes remain un- known so we cannot conclude that the turbine deaths are insignificant. When considered against a backdrop of other serious threats to bat populations, such as the spread of White-nose syndrome disease, habitat loss and pesticide use, the additional deaths from wind turbines constitute a substantial concern.
Finding a solution to this problem is therefore vital, not only because bats are important both ecologically and eco- nomically as the only major predator of night flying insects but also because any impediment to the expansion of wind energy generation delays efforts to reduce carbon emissions and diminishes the global response to climate change.
If bats were to suddenly disappear, the resulting increase in insect populations would lead to food crop damage that could threaten food security, and increased risks to humans from insect-borne diseases.
This white paper proposes a solution to this threat to bat populations by drawing on principles from the science of behavior and training. It is possible to replace problem behaviors with more desirable ones through changes to the environmental arrangement making the desired behavior more likely to occur and to maintain those behaviors using reinforcement. The desired replacement behavior in this case would be for the bats to use safer migration routes that avoid close contact with wind turbines. To achieve this, I propose the establishment of “migration corridors” of inter- connected bat-friendly habitat that provide the bats with significant motivation to conduct their feeding, roosting, and mating away from the dangers of wind turbines.
There is already a substantial body of research and knowledge on what bats need to thrive and the types of natural habitat that contain the resources that attract and sustain them during migration. By using this knowledge, potential routes could be assessed and selected based on their suitability to facilitate the movement of migrating bats by provid- ing the maximum possible percentage of bat-friendly resources. Routes should be selected that have stepping-stones of habitat sufficiently close together to ensure the bats will continue to follow the “breadcrumb trail”, while remaining far enough away from any existing or planned wind farms that their attraction (whatever that may be) cannot be perceived by any sensory modality, so that the majority of bats would be guided, undistracted, safely past the turbines.
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To do so we would not need to build migration corridors from scratch; joining already existing habitat such as state parks, preserves, and other protected or private land areas, would connect one green haven to another. Using existing arteries such as rivers, mountain ranges, forests, and greenways we could achieve maximum functional connectivity to attract migrating bats.
The establishment of wildlife corridors is not a new idea. The US Fish and Wildlife Service and its partners already manage habitats in four major “flyways” facilitating the protection of migratory birds as they travel between nesting and wintering areas. There are also several established wildlife corridors in North America for migrating land animals such as Y2Y, an interconnected system of wild lands and waters stretching from Yellowstone to Yukon; the Florida Wildlife Corridor, a statewide network of protected lands, waters and wildlife crossings that help to protect species such as the endangered Florida Panther; and a recently introduced grant program in several western states to con- serve habitat and work with private landowners to ensure safe passage of migrating elk, mule deer and pronghorn. There have even been some attempts to establish protected ocean corridors or “swim-ways” to protect migratory routes for key marine species.
There are multiple economic and environmental advantages to this approach that unify conservation with both eco- nomic and political goals. Funding efficiencies can be maximized for the benefit of multiple stakeholders, including wind energy companies, farmers, conservation groups, and the public. Furthermore, this approach would simultane- ously assist the conservation efforts for multiple other species and complement current federal and state conservation planning and legislation.
This proposal provides a unique opportunity for the collaboration of multiple stakeholders and the integration of a multi-disciplinary approach from a variety of professional and research disciplines. Its success relies on conservation groups, land trusts, farmers, energy companies, meteorologists and government agencies working together to provide the expertise, management, land, and funding.
The objective of this white paper is to inspire interested stakeholders to explore the idea further and to provide lead- ership for the formation of a project team to implement a pilot study to test the efficacy of the proposal and to ensure that there are no unforeseen side effects or unintended consequences. If bat migration corridors prove to be success- ful at reducing bat fatalities around wind farms, then the results should be published to encourage the creation of migration corridors everywhere there are wind farms.
3 Background on Wind Turbines and Wildlife
Migrating bats are colliding with wind turbine blades as they travel between summer and winter habitats or hibernac- ula. A recent global review (O'Shea, Cryan, Hayman, Plowright, & Streicker, 2016) has shown that wind turbines and white-nose syndrome (White Nose Syndrome Response Team, n.d.) are the biggest causes of bat mortality worldwide. There are a number of difficulties in estimating exactly how many bats are being killed by turbines (Huso, 2011), but a study conducted in Canada (Zimmerling & Francis, 2016) determined that an average of 15.5 bats were killed per turbine each year. If this number were extrapolated to the United States’ current total of 63,003 turbines (Hoen, et al., 2020) it would equate to over 900,000 bat deaths every year in the US.
In the United States, wind energy companies can be prosecuted under the Endangered Species Act (ESA) when a fed- erally protected animal dies as a direct consequence of the construction or operation of their business. Voluntary guidelines (U.S. Fish & Wildlife Service, 2012) encourage them to obtain permits from the US Fish and Wildlife Service (USFWS) for the “incidental take” of federally protected wildlife. Incidental Take Permits are predicated on the com- pany identifying pre-construction measures to minimize the risk to wildlife and post-construction measures to monitor casualty numbers via carcass surveys and in 2016, the USFWS extended the maximum permit duration from five to thirty years.
The American Wind and Wildlife Institute’s Information Center (AWWIC) holds the most comprehensive database of post-construction studies of wind farms in the US and their first technical report (Allison & Butryn, 2018), contains data on actual carcasses found and collected by researchers from 146 wind projects. The majority of these studies were conducted using human searchers, who, in most cases, can only effectively search the paved roads and pads as compared to trained conservation dogs who generally search much larger areas (around a 70-100m radius of a single turbine). Dogs are also more than three times more efficient than human searchers (Mathews, et al., 2013), although carcass data from either source are still imperfect (Huso, 2011) and must be adjusted to account for missed carcasses and those removed by avian and mammalian scavengers before searchers arrive.
Four species of bats found in Indiana currently benefit from protection. Two species, the Indiana bat (Myotis Sodalis) and gray bat (Myotis griscens), are listed in the ESA as Federally Endangered. Northern long-eared Bats (Myotis sep- tentrionalis) are listed in the ESA as Federally Threatened while the evening bat (Nycticeius humeralis) is State Endan- gered. Of the forty seven bat species found in North America, twenty four species have been found as fatalities at wind energy facilities (Arnett & Baerwald, 2013). Whilst post-construction surveys collect mortality data on all the affected bat species, the focus of concern is primarily upon those species protected by the ESA with the assumption that fatalities in other species are not substantial enough to cause adverse population affects. However, given that we lack basic demographic information about these species, some research (Frick, et al., 2017) has warned that unless measures to reduce the mortality from turbines are initiated soon, fatality numbers could reduce population sizes by up to 90% and increase the risk of extinction of the unprotected species.
None of the species most affected by turbine deaths in the Midwest - the eastern red bat (Lasiurus borealis), the big brown bat (Eptesicus fuscus), the silver-haired bat (Lasionycteris noctivagans), and the hoary bat (Lasiurus cinereus) - are protected by any current conservation laws, despite the fact that these migratory species collectively constitute the vast majority of reported fatalities at wind power facilities in all North American regions collectively (Allison & Butryn, 2018).
Biologists first began finding bat carcasses beneath wind turbines in the late 1990s while conducting studies of bird fatalities (Johnson, et al., 2003). Prior to that, bat collisions with other tall man-made structures were rarely reported so this was an unanticipated phenomenon. Scientists therefore initially hypothesized that the rapid decrease in air pressure around the spinning blades was causing internal bleeding from barotrauma when bats flew too close 4 (Baerwald, D'Amours, Klug, & Barclay, 2008). However, this theory was largely discounted in 2012 when a study pre- sented at the ninth biennial Wind Wildlife Research Meeting in Denver, Colorado by the National Renewable Energy Laboratory, suggested that pressure differentials large enough to cause barotrauma is limited to a small area along a rotating turbine blade and that if a bat were that close, collision would be almost inevitable (Office of Energy Efficiency & Renewable Energy, 2013). Further forensic investigation that year of collected carcasses concluded the vast majority of deaths result from traumatic injury when bats actually strike the spinning blades (Rollins, Meyerholz, Johnson, Capparella, & Loew, 2012).
The first major study focusing solely on bat deaths at turbines (Arnett, Huso, Schirmacher, & Hayes, 2010) took place in 2004 when the newly formed Bat Wind and Energy Cooperative (BWEC) commissioned wildlife biologist Ed Arnett to search for bat carcasses with his dog at the Casselman Wind Power Project in Pennsylvania (Mathews Amos, 2016). Arnett’s work provided empirical evidence that bat deaths could be significantly reduced by only allowing the turbines to cut-in when wind speeds are above that which most bats are active. Turbine blades can either be feathered (Arnett, Huso, Schirmacher, & Hayes, 2010, p. 211 Fig 2) where they are pitched parallel to the wind so they can only move slowly, or curtailed where they are prevented from spinning until a certain wind speed is reached. These methods remain the primary mitigation protocols applied to reduce bat deaths.
In addition to bat deaths, carcasses of approximately 250 species of birds have been found beneath wind turbines in the US Most of these fatalities involved perching songbirds or passerine species during their spring and fall migrations (American Wind Wildlife Institute, 2016). Early turbine design, such as those built in the 1980s in the Altamont Pass in California used a lattice design for the turbine supports and scientists quickly realized that this provided multiple perches attracting birds to the turbines (Lautamo, 2016). Later models were fitted with a smooth monopole design which improved this issue and as a result, passerine casualty estimates are down to less than 0.01 percent of their total population (Murphy & Anderson, 2019). It should be noted that most migratory birds travel at heights above those of the majority of wind turbine towers and also that the nuclear and fossil fuel industries kill around fifteen times more birds (Chapman, 2017). However, the siting of some turbines on migratory bird flyways appears to have a greater influence over the fatalities of larger bird species such as raptors. These birds may be more vulnerable to collisions due to their tendency to gather in groups on ridge-tops and upwind slopes (areas that also make good sites for wind farms), or it may just be that their large carcasses are easier to detect.
Following prosecution in 2013 for the death of more than 150 protected birds (Opar, 2013), including fourteen Golden Eagles, Duke Energy Renewables installed a camera-based identification technology called IdentiFlight® Aerial Detec- tion System (IdentiFlight, n.d.) to recognize protected raptors and to shut down (curtail) the turbine blades when the birds got within a certain distance. Evaluation results of the IdentiFlight® system (McClure, Martinson, & Allison, 2018) look promising and other monitoring systems are already in use that utilize data from the radio/ GPS monitoring sys- tems attached to heavily protected birds like the California Condor to curtail blades when a signal is detected nearby (Bennet, 2018).
As yet, there are no such monitoring systems in place to alert wind farms of the presence of nearby bats in order to curtail blades, however, research over the past two decades has increased our knowledge and understanding of bat behavior in relation to turbines. We now know, for example, that bat fatalities increase before and after the passage of storm fronts (Arnett, et al., 2008) and that the activity of migratory bats decreases when the prevailing wind is from the north or northeast (Baerwald & Barclay, 2011) and that different bat species differ in their response to these factors. While the activity (and thus fatality) levels of all tree roosting bats increased in warmer temperatures and lower wind speeds, it also showed that the fatalities of silver-haired bats increased when winds were from the south- east while fatalities of hoary bats increased with falling barometric pressure. This type of research increases our
5 knowledge of how environmental variables contribute to the risk that wind turbines present to bats and provides an opportunity to develop smarter mitigation protocols that are contingent upon these factors
Why Reversing Bat Population Decline is so Important
Although the exact bat fatality totals are unknown, the numbers are significant enough to warrant serious concern for several reasons:
1) Bats are incredibly important to ecosystems and one of the “most overlooked, yet economically important non- domesticated animals in North America” (Boyles, Cryan, McCracken, & Kunz, 2011). A significant decline in bat num- bers, or the loss of any single species, could have a devastating effect on global ecology. “There are more than 1,390 species of bats around the world playing ecological roles that are vital to the health of natural ecosystems and human economies.” (Bat Conservation International, 2020). For example, they are important predators of night flying insects (Donahue, 2017) and are estimated to save farmers billions of dollars each year in natural pest control (Bennett C. , 2016). A 2011 analysis at the University of Tennessee found the economic impact of the loss of bats for North American agriculture to be in the range of $3.7 to $53 billion a year (Boyles, Cryan, McCracken, & Kunz, 2011). For example, Bracken Cave in Texas is host to the largest known insectivorous bat roost in the world. These Mexican free-tailed bats (Tadarida brasiliensis) primarily eat corn ear-worm (Helicoverpa zea) moths, which are agricultural pests that cause millions of dollars’ worth of damage to crops each year (Bennett C. , 2016). Bats could also prove to be vital in the fight against some invasive agricultural pests (Maslo, et al., 2017), such as the Asian brown marmorated stink bug (Halyomorpha halys) or the cucumber beetle (Acalymma vittatum or Diabrotica undecimpunctata howardi), whose larvae are a major pest of corn (Whitaker, 1995).
2) A rapidly expanding wind energy industry poses increasing risk to multiple bat species at a time when bat deaths are already on the rise globally and bat populations are already under extreme stress from White-nose Syndrome (O'Shea, Cryan, Hayman, Plowright, & Streicker, 2016), habitat loss and pesticide use (Frank, 2018). Added to this is the fact that bat populations are slow to recover from mass mortality events (O'Shea, Cryan, Hayman, Plowright, & Streicker, 2016) because they are long-lived animals that reproduce slowly (Barclay, et al., 2004), with most species producing only one pup per year. Research from over ten years ago already found evidence of declining numbers of eastern red bats (Winhold, Kurta, & Foster, 2008) and recent research (Rodhouse, et al., 2019) using monitoring data from the North American Bat Monitoring Program (NABat) has found evidence of a decline in summer populations of the hoary bat in the Pacific Northwest.
3) Given that wind energy forms a vital part of the global effort to reduce carbon emissions to combat climate change, bat deaths are a potential public relations issue. Concern for bat population health could provide climate skeptics and fossil fuel advocates with arguments to disrupt this industry's growth and increase regulatory and economic hurdles to achieving the production levels needed to avoid catastrophic warming levels.
Research Into the Causes of Bat Fatalities at Wind Farms
Recent studies of bat physiology reveal that bats are supremely competent flyers and use less energy than do birds (Than, 2007). Rather than being rigid structures, their wings consist of many separate bones and joints covered by a thin membrane of skin. According to researchers at Brown University the bones vary greatly in mineral content making them “very stiff near the body to nearly cartilaginous and highly compliant at the wing tips” (Aeromechanics & Evolutionary Morphology Lab, n.d.). The combination of these features creates a structure that can form an extraor- dinary range of shapes to create more lift with less drag and hence provide more maneuverability. In addition to being 6 able to see reasonably well with their eyes (Caspermeyer, 2019), bats also have enhanced echolocation abilities that allow them to detect and avoid moving objects better than stationary ones (Jen & Mccarty, 1978). So why do bats fly into turbine blades in such significant numbers?
Despite two decades of research (Cryan & Barclay, 2009), the precise reasons why bats are being killed at turbines are still unknown but patterns can be discerned from the carcass surveys. The AWWIC's preliminary data (Allison & Butryn, 2018), reveals that the vast majority of bats killed are those that roost in trees and migrate long distances. There is also a very stark seasonal peak in fatalities in late summer into autumn which coincides with fall migration when there is both increased feeding activity and mating behaviors before hibernation.
Bats use sonar to avoid obstacles and to hunt small insects but the range of most species’ echolocation is short - limited to approximately 50-100m (Boonman, Bar-On, Cvikel, & Yovel, 2013) - beyond this distance bats rely more on their vision for perceiving large landscape features (Gorresen P. M., Cryan, Dalton, Wolf, & Bonaccorso, 2015). A United States Geological Survey (USGS) led study (Cryan & Brown, 2007) examined 38 years of migratory date records for hoary bats to a small isolated island stopover point near to San Francisco. USGS cross-referenced these dates with weather records and discovered that the bats were more likely to arrive on the island with passing storm fronts and that wind speed, moon illumination and barometric pressure are important predictors of bat movements. They also discovered that migrating hoary bats appeared to be drawn to tall, visible features like the island’s lighthouse. More recent research at wind turbine sites in the US (Cryan P. , et al., 2014) and in Canada (Baerwald & Barclay, 2011) has showed that both bat activity and fatalities at turbines increased when the moon’s illumination was full or gibbous which suggests that vision plays a role in the attraction process.
During experiments at a wind facility in northwestern Indiana in the fall of 2012, three turbines were fitted with infra- red cameras to watch individual bat/turbine interactions, acoustic detectors to identify species via ultrasonic calls, and radar to monitor the overall numbers of bats and other aerial creatures flying through the area (Cryan P. , et al., 2014). More than 1300 hours of thermal video were recorded over the course of 163 nights and 90% of the bats caught on camera could be seen actively approaching the turbines. Another study observed bats “actively foraging near op- erating turbines” and indicated that bats “investigated the various parts of the turbine with repeated fly-bys” (Horn, Arnett, & Kunz, 2008). These observations led researchers to conclude that the deaths were not random events but rather that the bats were visually perceiving the turbines and were deliberately changing course in order to approach them. This led them to surmise that the bats were equating the characteristics of the turbines with those of tall trees and approaching with the expectation of accessing resources such as food, a mate, or a place to roost.
Unlike birds, migrating bats tend to fly at lower altitudes and feed as they travel which potentially brings them into closer contact with turbines. One theory posits that insects may concentrate around wind turbines (Rydell, et al., 2016) and research seems to confirm that the “pure white” and “light grey” colors often favored in wind turbine design does increase insect activity (Long, Flint, & Lepper, 2011). A study of the stomach contents of dead hoary bats showed that bats were indeed feeding in the area before they were killed but a lack of prey in the mouths or throats of the bats (Valdez & Cryan, 2013) brings into question the hypothesis that bats are struck by the blades while actively hunting.
The rapidly spinning blades certainly kill insects as well, and the accumulated “dead insect” smell on turbine blades may also help to attract the bats. Researchers at the Institute of Engineering Thermodynamics at the German Aero- space Center have also linked the migration of insects and the migration of the bats that feed on them (Trieb, 2018). It is known that the vast majority of migrating insects take advantage of faster air currents above the earth’s atmos- pheric boundary layer for long range movement (Reynolds, Chapman, & Drake, 2017) and taller modern turbines reach high enough into this layer to interfere with this movement (Rydell, et al., 2010). Some opportunistic insects have also adapted their behavior to capitalize on the warmth and shelter afforded by turbines and use them as overwintering sites (Dudek, Dudek, & Tryjanowski, 2015). What has been refuted however, is the notion that the flashing red aviation 7 lights on top of some turbines may attract insects and therefore bats. In fact, research at a utility scale wind facility in north Texas showed that bat fatalities were higher at the wind turbines without aviation lights (Bennett & Hale, 2014).
Bats caught on camera in Indiana in 2012 appeared to be more interested in the nacelles that house the motors than in the towers or moving blades (Flatt, 2014), which supports theories that the bats are approaching the turbines and attempting to roost in them. Indeed, hoary bats and eastern red bats were seen approaching the nacelle’s exhaust ports from the down-wind side and analysis of their flight patterns suggest that they were trying to land. In addition, it is thought that the tallest trees in the landscape may serve a rendezvous function for sexually mature bats during the breeding season (Cryan, et al., 2012) but there are many factors that make it difficult to gather sufficient data to confirm this hypothesis. For example, the ability of both male and female bats to retain viable sperm inside their bodies for long periods makes the precise timing of mating events difficult to estimate based on anatomy alone, and many of the carcasses collected cannot be analyzed due to the level of decomposition (Cryan, et al., 2012).
Biologists Victoria J. Bennett and Amanda M. Hale at the Texas Christian University were funded by the US Department of Energy in 2018 (Bennett & Hale, n.d.) to explore a theory that the bats were confusing the smooth surfaces of the turbines for water based upon observations of their flight approach behaviors (Connelly, 2016). The researchers cre- ated an indoor “bat flight facility” in which they could observe the behaviors of captured bats with different materials and textured paints and they observed a significant reduction in bat activity at distances under 1 meter from the vertical textured surfaces as compared to the smooth ones (Stafford, 2016).
All this research has certainly increased our knowledge of these elusive mammals and brings us closer to understand- ing the causes of the fatalities, however further research is still needed as the data remains insufficient to determine exactly why bats are attracted to, and killed by, wind turbines in such numbers. It is also likely that hypotheses and causal explanations need to be investigated at the species level due to evidence (Baerwald & Barclay, 2011) that be- havioral tendencies and response to stimuli differ greatly between species (Cryan & Barclay, 2009) and often even within them (Zubaid, McCracken, & Kunz, 2006). While we wait for answers to these questions there are many people and organizations dedicated to seeking solutions and there has been much progress.
Pre-Construction and Post-Construction Mitigation Strategies
Organizations like the National Wind Coordinating Collaborative (NWCC, n.d.) and the Bats and Wind Energy Cooper- ative (BWEC, n.d.) are investing money and resources into developing solutions to the problem of bat mortality and their work focuses on three main areas – improving the siting locations of wind farms through pre-construction mon- itoring of bat activity levels; post-construction fatality searches to determine patterns and improve our understanding of species, weather and habitat variables; and supporting the research and development of deterrents and mitigation tools. The wind industry is also lending its financial weight to the problem and in 2019 thirty companies pooled re- sources and created the industry-led Wind Wildlife Research Fund (AWWI, n.d.) in order to centralize funding and collaborate on research. Siting and surveillance Bat detection methods are constantly improving (Cryan & Gorresen, 2014). Thermal and near-infrared cameras are getting cheaper and more able to withstand extended exposure to extreme conditions with fully weatherproof casings and longer battery lives. Equipment to record the ultrasonic calls of bats are becoming more sophisticated (Wildlife Acoustics, n.d.), as are the software tools with which to analyze them (Aodha, et al., 2018). Improvements are also being made to the way that raw data from carcass surveys are converted to project-wide fatality estimates. Statisti- cians at the USGS recently collaborated with developers of previous models to create a single unified tool called the
8 Generalized Mortality Estimator (Simonis, et al., 2018) which should improve accuracy and facilitate easier compari- son of data between sites. To that end, in 2018 a PhD student from Texas conducted a year of carcass monitoring at two wind facilities and used the GenEst to analyze and compare results (Weaver, 2019). All this development will help to reduce risks by informing siting strategies and improving the surveillance of existing sites. Curtailment and deterrents Meanwhile, increasing the wind speed at which turbine blades cut-in speed (curtailment), remains the most widely employed mitigation strategy and new technology is being developed to reduce the cost of lost production (Pearcey, 2019) which is currently estimated to be at least 5% (Speerschneider, 2019). Researchers are exploring not only the question of optimal cut-in speed to protect the majority of bats, but perhaps more pertinently, other factors that could be used as triggers for curtailment such as temperature (Peterson, 2018), the passage of storm fronts (Arnett, et al., 2008), and the phases of the moon (Cryan P. , et al., 2014). The term smart curtailment has been coined for this optimization by combining wind speed data with meteorological data and even real-time detection of bats in the area (Normandeau, 2019), to arrest turbine blades only when risk of collisions are high. Work in this area is already under- way and in March 2019, the US Department of Energy awarded a total of $2.8 million to four companies to advance their smart curtailment technologies (DoE, 2019).
Currently in development and being tested by several companies and institutions are deterrents that aim to keep the bats outside of the rotor windswept zone by effectively “jamming” their navigation systems with the broadband trans- mission of audible signals in the same range that the bats use for echolocation. The first generation of these ultrasonic acoustic deterrents were tested in 2009 during a two-year study in Pennsylvania (Arnett & Baerwald, 2013). The study found that while fewer bats were killed per treatment turbine than per control turbine, these results varied by species, and evidence of a strong effect was inconclusive when variations between turbines were considered. The study also recognized that because ultrasound attenuates rapidly with distance and humidity, the area over which it can be broadcast is limited so multiple devices are needed on each turbine in order to cover the entire wind-swept zone, which could make this approach costly to deploy and maintain site-wide.
Since that time acoustic deterrent devices have continued to improve and in 2019 three organizations, the National Renewable Energy Laboratory, General Electric Renewable Energy and Iowa State University, were awarded a total of $1.4 million (DoE, 2019) to develop, improve and evaluate the effectiveness of acoustic deterrents (Kinzie, et al., 2018). Previous research by the General Electric Company (Kinzie & Miller, 2018) showed that ultrasonic deterrents primarily affected the foraging behaviors of bats and discovered that both continuous sounds and pulsing ultrasonic signals were effective in displacing bat activity from the study turbines.
In May 2019 NRG Systems Inc announced the first commercial sale of its acoustic bat deterrent system (NRG, n.d.) to Hawaii's largest wind farm, Kawailoa Wind, to help protect the endangered Hawaiian hoary bat (Lasuirus cinereus semotus). Previous field tests (Video, 2016) of this system were conducted around ponds using thermal imaging cam- eras and, while showing a significant reduction in bat activity, these tests also showed that the bats did not leave the area completely. Instead they continued to “probe” the zone covered by the devices and returned to previous activity within minutes of the devices being turned off. More research is needed into the behavioral responses of bats in the presence of ultrasonic sounds (Kinzie & Miller, 2018) and all of these approaches to determine the best and most cost effective deterrents. In July 2019 Duke Energy Renewables began a five year installation program of the NRG Bat Deterrent System on 255 wind turbines at two sites in Texas (Froese, 2019) and Danish wind turbine manufacturer Vestas Wind Systems announced a strategic partnership with NRG Systems to offer their Bat Deterrent systems as an upgrade for all Vesta’s turbines (NRG, 2019).
9 Other deterrent approaches have been tried using systems that warn the bats of the presence of the turbines in the hope that they will then avoid collision. A novel approach explored in a 2014 experiment in Hawaii showed that illuminating tall trees with dim flickering ultra-violet light reduced the nearby activity of the Hawaiian hoary bat de- spite an increase in the number of insects (Gorresen P. M., Cryan, Dalton, Wolf, & Bonaccorso, 2015). In May 2019 a team from Texas A&M University presented findings to the Acoustical Society of America regarding their exploration of a biomimetic acoustic whistle to warn bats of the presence of turbine blades. The whistle, which is loosely modeled on the bat larynx, is mounted on the blades and emits multi-harmonic tones that can be detected by most of the impacted bat species from distances approaching 100 meters away (Smotherman, Sievert, Dowling, Carlson, & Modarres-Sadeghi, 2019).
Motivating Safer Behavior with Bat-Friendly Corridors
While all this vital work continues, the science of behavior analysis offers another approach that would complement these ongoing efforts. By widening our perspective to include all our existing knowledge of natural bat behavior, we can begin to consider what the bats could be doing instead of risking investigation of the turbine structures and flying close to the spinning blades. Framing the problem in this way reveals a different starting point and with-it new oppor- tunities for exploring solutions that do not focus on suppressing the unsafe behavior, but instead look for ways to encourage safer natural behaviors which are incompatible with unsafe turbine investigation. This shift of perspective invites the question “how do we motivate bats to follow safer migration routes?”, and by asking it, we become inspired to think about migration from a bat’s perspective.
Although many aspects of bat behaviors remain elusive, there is still a substantial body of research and knowledge on what bats need to survive and the types of natural habitat that contain the resources that attract them and sustain them during migration. We know for instance, the types of night-flying insects preferred by bats and that open bodies of fresh water are required to allow them access to drink on the wing (Sheppard, 2017). We know the roosting pref- erences of each species, some favoring loose bark, cavities, and crevices in dead trees while others prefer rocks or man-made structures, such as old barns, buildings or bridges. We have also developed sophisticated listening devices to pick up and analyze the calls they use to connect with, and to follow, each other and to attract mates.
By pooling all this knowledge and combining it with meteorological data on fall weather patterns we could plan and establish corridors of interconnected habitat that include the resources that migrating bats need and therefore pro- vide the bats with safer opportunities to conduct their feeding, roosting and mating behaviors elsewhere in natural habitats. The corridors could be enhanced with numerous properties known to be attractive to bats and provide mul- tiple incentives for the bats to follow these natural routes rather than adjusting their flight paths to investigate the turbines.
Ecologist Jodi Hilty explains in the second edition of her book, Corridor Ecology (Hilty, Keeley, Lidicker, & Merenlender, 2019), the science of habitat corridors has advanced significantly due to research results from projects all over the world. This work has shown that migratory animals are one of the groups most likely to benefit from the creation of habitat corridors. By providing corridors of bat-friendly habitat that repeatedly and abundantly satisfy their explora- tory search for food and shelter we would be providing bats with a way to fulfill their needs at a safe distance from wind turbines. The most vital aspect of this type of guidance is that the animal does not have any direct interaction with humans. The incentives for the bats must therefore be provided in such a way that they come from the natural environment as much as possible.
This does not mean we need to build migration corridors from scratch (although some habitat may be provided this way). The corridors would primarily be established by joining up already existing habitat such as state parks, preserves 10 and other protected areas by connecting one green haven to another and then utilizing, where possible, existing arteries such as those determined by rivers, mountain ranges, forests and greenways, to achieve maximum functional connectivity. It is essential to select routes that a) offer habitat stepping-stones close enough together to ensure the bats will follow the “bread-crumb” trail of incentives consisting of private wooded lots, parkland, land trust properties, wetlands, restored prairie, forest areas and nature preserves and b) that the corridors should go around areas of existing or planned wind farm development at a safe enough distance that their attraction (whatever that turns out to be), cannot be perceived by any sensory modality so that the majority of bats would be guided, undistracted, safely past the turbines.
This process would begin with the examination of map data to identify potential corridor routes based on the location of existing and planned wind farms, current bat habitat, and meteorological data on fall weather patterns that may affect when and where bats chose to fly. We know what bats need to thrive so routes should be assessed and selected based on their suitability in terms of the degree to which the landscape impedes or facilitates the movement of mi- grating bats. Habitats included in the corridors would be chosen that contain the maximum possible percentage of existing natural bat-friendly resources to minimize the requirement for new habitat creation or man-made embellish- ment. Water may be provided by following existing streams and rivers and by including ponds and lakes in the corridor routes. Planting additional trees in these areas will create riparian zones that increase their appeal as will planting prairie and native flower gardens. Where land is available, native grassland habitats could also be created or restored that border the wooded lots. This would provide night-time hunting grounds for the bats and additional habitat for diurnal species.
Entomologists should be consulted regarding ways to attract moths and other nighttime insects favored by bats. Na- tive plants and flowers such as Evening primrose (Oenothera biennis) and foamflower (Tiarella cordifolia) that release their scent at night and flourish in shady conditions should be added to the habitat along with plants that will provide food for caterpillars. Materials such as dead branches and leaf litter should be left to accumulate to provide winter protection for beneficial insects supported by the provision of man-made insect and bee houses. The value of this habitat could then be further enhanced in several ways to increase its attractiveness to the bats. For example, man- made roosting boxes of the type favored by target species (Hoeh, Bakken, Mitchell, & O’Keefe, 2018), could be built extensively throughout these sites to provide immediate additional roosting opportunities.
Individual sites included in the habitat corridors should be assessed and selected based upon the preferences of each of the target species in order to satisfy, for instance, the needs of solitary crevice roosting species like the silver-haired bat (Barclay, Faure, & Farr, 1988), those that prefer trees with foliage like the hoary bat (Willis & Brigham, 2005), to those that alternate between roosting in trees and roosting on the ground in leaf litter when temperatures approach freezing like the eastern red bats (Mormann & Robbins, 2007). Factors such as the variety of tree species, height, diameter, quantity of dead wood and debris and extent of timber management should all be considered (Crampton & Barclay, 1998). Research has also looked at how the presence of predators influences the behavior of bats and there have been some observations (Lima & O'Keefe, 2013), consistent with the suggestion that predation risk affected their choice of roosts, movement paths, feeding areas and emergence times so these factors should also be considered when selecting corridor sites (Arndt, O'Keefe, Mitchell, Holmes, & Lima, 2018).
Fall migration is a rare time when solitary bat species such as the hoary bat travel together in larger groups (Tuttle, 1995) and we can use this to our advantage by broadcasting social call recordings at this time to encourage bats in the area to approach and investigate. Research from as far back as 1982 (Barclay R. , 1982) showed that bats will approach when recordings of conspecifics are broadcast to them and that they will do this while engaging in a variety of behav-
11 iors including foraging for food, looking for night roosts, approaching nursery colonies or hibernation sites and search- ing for mates. Researchers have explored which senses forest-dwelling bats used to locate roosts and found that males may attract reproductive females to roosts using vocalizations (Ruczynski, Kalko, & Siemers, 2007). While other research found that although bats do recognize the calls of their own species they will also respond to the calls of other species when searching for new roosts (Schöner, Schöner, & Kerth, 2010). A 2015 thesis found significantly higher bat activity after broadcasting social calls and that this activity remained high after playback treatments had ended demonstrating a latent effect of playbacks at roosting sites (Brokaw, 2015). In addition to responding to calls of both their own and other species, there is research suggesting that insectivorous bats will also adjust their behavior to imitate that of another individual (Gaudet & Fenton, 1984).
Initially the corridor habitats may be partially contrived and include multiple man-made features and embellishments that require regular management and intervention. However, by planting additional trees of the specific species and type that are favored by tree-roosting bats, over time this intervention could be phased out as trees and plants grow and thrive and the natural ecology diversifies and expands. By building several of these routes throughout the state of Indiana we can create networks of corridors that provide bats with the migratory connectivity they need to maintain viable populations and gather data on the effect that this intervention has on the number of bat fatalities at Indiana wind farms (Cryan P. , 2011).
Examples of Similar Successful Conservation Interventions
When the first batch of captively bred California Condors were released into the wild in 1992 they had no learning history telling them to fear humans and as they began gathering at a small town near the release site, they were at risk of electrocution from power lines (Stammer, 1992). It took internationally-known bird expert Steve Martin (Natural Encounters, n.d.), to recognize they lacked the survival skills that would normally be taught by their parents in their first two years of life. Instead of focusing on how to scare the birds away from the town he began modifying the environment to supply randomly timed food provisions to teach the birds that it was beneficial for them to stay up in the mountains. The random contingency was also applied to the type of food, the quantity of food and its location. This variability was an important part of teaching the birds how to forage within their natural habitat while they gradually learned how to survive in the wild (Lombardi, 2018).
Ken Ramirez is a biologist and animal behaviorist and a more than forty year veteran of animal care and training, who has held roles at and consulted for zoos and aquariums throughout the world (Ken Ramirez Training & Consulting, n.d.). He pioneered the application of his skills to wild animals in a conservation setting with the use of a technique he calls “remote training” (Ramirez, 2019). This approach has had numerous successes with multiple species, including Chimpanzees in Sierra Leone who were taught to scream in unison to alert rangers at the nearby station of the ap- proach of poachers, and polar bears in Alaska who were dissuaded from approaching human settlements (Cartlidge, 2019). Ramirez’s latest conservation project is changing the migration route of a population of elephants in Zambia to go around a section that had them crossing through the Democratic Republic of Congo where they were being killed by poachers (Ramirez, The Steep Price of Conservation, 2017). When fences failed to deter the elephants, a ten-year project began that, each year, strategically places temporary man-made water holes to reinforce them for selecting the new route. The elephants only migrate that way once per year so the project has only ten opportunities to shape the new behavior before it is scheduled to complete in 2027; by then it is hoped the elephants will have received enough of a learning history that they permanently adopt the new route. So far it is working, and in the project’s first year it successfully rerouted 374 elephants with only four reported deaths, none of which due to poaching. In the previous four years between sixty and seventy elephants had been lost to poaching annually (Association of Zoos and Aquariums, 2019). 12 The Benefits of this Approach
There are numerous potential benefits that could be realized by the formation of bat-friendly habitat corridors. These include:
1) Funding efficiencies through the unification of conservation goals: The publication of several prominent reports in the past year (see further reading below), shows there is heightened focus on this issue and consequently multiple sources of available funding aimed at solving the conflict between bats and wind turbines (AWWI, n.d.). The creation of bat-friendly habitat corridors would not only benefit bats but many other declining species such as birds, butterflies and bees so this is a unique opportunity to combine funding with other conservation initiatives to create a wide- ranging project that utilizes limited economic resources. Examples of other conservation initiatives with objectives that coincide with this proposal are the Grasslands for Gamebirds and Songbirds Initiative (INDNR, n.d.), E.O. Wilson’s half-earth project (Half-Earth Project, n.d.). Douglas Tallamy’s book Nature’s Best Hope explains how individuals have the power to use their own backyards to create twenty million acres of interconnected habitat that he calls a “home- grown national park” (Tallamy, 2019).
2) Complements federal government conservation planning: This project proposal is in harmony with three major pieces of proposed conservation legislation. The first is an endeavor spearheaded by US Fish and Wildlife Service under the National Environmental Policy Act to create a Multi-Species Habitat Conservation Plan (MSHCP) covering eight Midwestern states (Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio and Wisconsin), to meet the growing demand for rapid approval and incidental take permitting of future wind energy projects (U.S. Fish and Wildlife Service, 2019). The second is the Wildlife Corridors Conservation Act (Heltne, 2019), a bill introduced to Congress on May 16 2019 that aims to address the fragmentation of wildlife habitat by providing a program for the protection and restoration of wildlife corridors on both federal and non-federal lands (116th Congress 1st Session, 2019). The third is the Recov- ering America’s Wildlife Act, a bi-partisan bill introduced to Congress on July 12 2019 (116th Congress, 2019) with the aim of securing dedicated funding to proactively reduce the number of endangered species and to prevent more spe- cies being added to that list.
3) Potential to benefit Indiana residents and increase environmental stewardship: This project would provide an opportunity to combine the objectives of conservation with those of the Indiana Statewide Comprehensive Outdoor Recreation Plan 2021-2025 (INDNR, n.d.) by incorporating recreational trail amenities inside the habitat corridors. By combining these objectives and building water sport, biking and walking trails within the wildlife habitat corridors, funding efficiencies could be increased even further, and funding sources pooled. There may be initial conservation concerns with regards to allowing public access to these habitats in the fragile early stages of species recovery. How- ever, the potential long term benefit of partnership with local communities is that research suggests that experiencing nature plays a key role in the development of pro-environmental behavior and stewardship (Kuo, Barnes, & Jordan, 2019). This tandem approach to human and ecological planning may be the best way to successfully secure our natural heritage for future generations.
4) Unique opportunity for collaboration and integration: This project calls for a multi-disciplinary approach between a variety of stakeholders, professionals and research disciplines. Its success relies upon conservation groups, land trusts, farmers, energy companies, meteorologists and government agencies working together to provide the exper- tise, the land and the funding. It will need Geographical Information System experts to study maps and help with planning the corridor routes; ecologists and bat biologists working in tandem with botanists and entomologists to create bat-friendly habitat; ethologists and behavior analysts to advise on behavioral contingencies; and engineers and forest managers to build the infrastructure. A 2018 study at Iowa State University demonstrated the value of different disciplines working together when engineers and bat ecologists joined forces to examine over 500 bridge
13 structures and created a database showing those used by bats as roosts (Postlethwait, 2018). The resulting data iden- tified certain structural characteristics that could be used to predict bat presence that will allow the Department of Transportation and the Federal Highway Administration to proactively plan bridge maintenance in the future without disturbing bat colonies (Bektas, et al., 2018). Integrated projects such as this, with multiple stakeholders working col- lectively toward common goals, result in greater mutual understanding and help to diffuse conflicts between ecology and economics.
5) Reduced economic impact of pest control: As the primary predator of night-flying insects, migrating bats provide free pest reduction services. Many species can eat nearly their own body weight in insects each night. Bats often follow corridors of forest when traveling from roosts to feeding areas where they play a vital role in maintaining the health of forest ecosystems by keeping the numbers of destructive insect pests in check (Taylor, 2006). As already discussed, this financial benefit will also be felt by farmers who currently spend billions of dollars each year on chem- ical pest control. A study of the guano of bats living in purpose built bat houses on organic pecan farms (Brown, Torrez, & McCracken, 2015) found evidence of the consumption of several crop pests including pecan nut casebearer (Acro- basis nuxvorella), hickory shuckworm (Cydia caryana ) and corn earworm (Cydia caryana). It is therefore vitally im- portant that we take urgent measures to protect bat numbers from declining further and provide habitat for maternity colonies to allow populations to stabilize and recover.
6) Reduced economic impact of curtailment: Numerous studies have shown that imposing a turbine cut-in speed at or above 5 m/s reduces bat fatalities with varying effect dependent upon local factors and an across-species average reduction of at least 50% (Arnett, Huso, Schirmacher, & Hayes, 2010). A 2011 study of Fowler Ridge Wind Energy facility in Benton County Indiana (Good, et al., 2011) has led the USFWS to suggest that curtailing turbines at between 6.5m/s and 6.8 m/s would circumvent fatalities of the Indiana bat (Myotis sodalis) altogether, therefore eliminating the need for take permits. The effectiveness of curtailment has resulted in an increased use of it as a compliance and regulatory tool. However, restricting turbine operation at low wind speeds results in a loss of production and costs the wind energy industry money. Economic studies have calculated that most wind energy facilities can tolerate a 1% reduction in production and revenues due to curtailment, however at loss levels of 5% or higher revenues deteriorate beyond that which is economically viable (Cheszes, 2012). While increased use of “smart curtailment” will provide part of the solution to this (Pearcey, 2019), the possibility that overall numbers of bats could be reduced around wind turbine sites, particularly during migration season, may allow energy companies to mitigate losses in production po- tential still further.
7) Reducing impediments to wind expansion will help to address climate change: The 2018 report on global warming by the United Nations Intergovernmental Panel on Climate Change (IPCC, 2018) warns that we have only twelve years to limit a climate change catastrophe and that in order to avoid global temperature rises of more than 1.5 degrees centigrade the pace and scale of carbon emission reduction needs to accelerate such that 50% or more of our “primary energy” needs are met by renewable sources by 2050. If habitat corridors can help to prevent the decline of bat species and restore population levels so that they no longer require strict protections then renewable energy businesses will be able to operate with fewer regulatory controls enabling them to expand to the levels required to address acceler- ating climate change. In shifting our focus from ways to solve the wildlife-wind energy conflict towards ways we can reduce and avoid it by building the habitat that wildlife needs to survive and thrive, we can develop a more adaptive planning approach (Köppel, Dahmen, Helfrich, Schuster, & Bulling, 2014) to the benefit of all stakeholders.
8) Opportunity to deepen our understanding of bat migration and social behavior: The bats most affected by wind turbines are migratory and travel tens to hundreds of kilometers each year from summer habitats to either caves or mines where they hibernate throughout the winter, or to lower latitudes where they continue feeding and sporadically
14 enter short periods of torpor when temperatures drop or prey becomes scarce (Popa-Lisseanu & Voigt, 2009). Accel- erating habitat and climate change make migratory behavior a topic of growing interest to researchers (Krauel & McCracken, 2013). However, tracking migrating bats is extremely challenging and as a result very little is known about where they originate, the routes that they take, whether they travel individually or in groups or how long they spend on the journey (Giavi, Moretti, Bontadina, Zambelli, & Schaub, 2014). To complicate matters further these factors most likely vary across species.
In 2007, Julie Zeyzus, a master’s student at Indiana University of Pennsylvania was part of a project that aimed to answer some of these questions by tracking the long-distance migration of Eastern red bats wearing miniature radio transmitters using a telemetry-equipped airplane and three ground vehicles (Zeyzus, 2009). The logistical difficulties of this task were vast and while their research showed that migratory bats could be captured and radio-tagged during fall migration, it also showed that without very close monitoring of the signals both from the ground and the air, bats can very quickly outdistance searchers and move into areas where radio signals are difficult to detect. Despite fifty years of bat tracking (O'Mara, Wikelski, & Dechmann, 2014) there are still many technical constraints and we are a long way from being able to build the kind of real-time models that are possible for bird migrations (National Geographic, 2017 ).
Building on earlier work (Cryan, Bogan, Rye, Landis, & Kester, 2004), two studies in 2014 used an alternative method to gain insight into bat migratory movements by analyzing the stable hydrogen isotope in the keratin of bat hair from wind farm fatalities (Baerwald, Patterson, & Barclay, 2014) and (Cryan, Stricker, & Wunder, 2014). The research found evidence of a migration routes along the eastern slopes of the Rocky Mountains that are used by hoary and silver- haired bats as well as along coastal regions, where temperatures remain above freezing, which may provide important over-wintering habitat for hoary bats.
Intentionally designed corridor habitats provide an opportunity to gather data on migrating bats in easier and more passive ways. If more robust corridors proved successful in providing adequate ecological resources to attract at least some percentage of the population of migrating bats to use the habitat as stop-off points on their travels, they would present known locations to implement a variety of bat monitoring technologies. Rather than attempting to track the real-time movement of individual bats, devices could be static and gather data as the bats pass through the area. Among the available options include, audio recording of the bats’ ultrasonic vocalizations to determine species and their exhibiting behaviors (Aodha, et al., 2018); beam sensors across the entrance of roosting boxes to monitor the bats arrivals and departures; and infrared cameras to conduct species identification and visual counts. Such equipment has been used by bat researchers all over the world and there are a number of companies which specialize in supplying this equipment (Bat and Conservation Management, n.d.).
The New Zealand Department of Conservation (NZDOC) has been using similar techniques to monitor bats and birds for decades and in their efforts to save a number of critically endangered species they have developed a number of innovative and unique technologies (NZ Department of Conservation, n.d.). For example, their Kakapo sanctuary is equipped with “smart hoppers” that automatically dispense food to specific birds while recording their weight without any direct human contact (Thomasy, 2019). In another innovative project the NZDOC glued tiny radio frequency iden- tification (RFID) tags to critically endangered robust grasshoppers in order to locate and track them with scanners in their natural habitat while they remained well concealed from their avian predators (Sounds of Science Podcast #4, 2019).
These devices are the size of a grain of rice and one specific type is already widely in use to identify pet dogs and cats. The electronic tags have an antenna which powers up when scanned by a reader to transmit its unique identification code. The advantage these devices have over radio transmitters is that they are extremely inexpensive, very small and lightweight, do not require batteries, and they last forever so there is no requirement to recapture the animals. The 15 downside is that the readers have a short range so are unsuitable for real-time tracking of long-distance migratory animals. However, if large numbers of bats were tagged in this way, and large numbers of readers were installed at roost entrances and the entrances of known hibernacula, then it would be feasible that this indirect tracking method could provide meaningful migration information at the level of the individual bat.
By incorporating a suite of technological bat monitoring equipment within the habitat corridors, large quantities of data could be acquired, not only to test the achievement of the project objectives, but also to contribute to the body of knowledge on bat migration and social behavior and to support continent-wide monitoring initiatives whose goal is to assess changes in bat populations and the effects of climate change on migration patterns such as the North American Bat Monitoring Project (NABat, n.d.).
Conclusion
In this paper I provided background on the issue of bat deaths at wind farms and explained why bats are so important to our ecology and require protection. I reviewed the research to date on the causes and described some of the strat- egies that are being explored or employed to mitigate bat fatalities. I then provided a detailed outline of a proposal to complement the package of solutions already being employed, offerred examples of where similar approaches have been successful, and listed the multiple potential benefits of this approach.
The research is unequivocal: migratory tree-bat fatality at wind turbines is a serious problem that may pose popula- tion-level concerns for some species. Equally clear is the urgent need to remove any impediments to wind energy expansion to achieve the degree of carbon pollution reduction necessary to protect both human and animal life from climate change. The use of deliberate and consciously planned habitat corridors to address both issues has numerous potential benefits. Not only would this be an efficient use of funding resources, but the scope of the project would also be scalable and could be built upon gradually, in phases, after its efficacy has been established.
The objective of this proposal is therefore to inspire interested stakeholders to explore and test this approach, begin- ning with a pilot project (possibly in the State of Indiana), involving a multidisciplinary team. If it is shown that habitat corridors are a viable way to provide bats with safe migration routes to follow, then the corridors can be expanded until they create a network of connectivity that provide migratory guidance for bats at sufficient distances from tur- bines throughout the Midwest. Connecting both small isolated patches and large expanses of habitat in this way will begin to address the fragmentation of our natural landscape for the benefit of all its native species, including us.
“In any endeavor we choose to embark upon, our success is limited only by our knowledge, our willingness to put forth the effort, and our imagination. Each of these things are only self-imposed limitations.” -Ken Ramirez
Acknowledgements
I would like to thank Whitney Yoerger, Coralie Palmer, Angus Lock, Eva Rudisile, Allyson Bradley, David Thatcher, Katy Gehan, Collette Holden, Hannah Davie and Rosalie Benitez for their invaluable assistance with editing and references; Dr Allen Kurta and Associate Professor Joy O’Keefe for graciously answering my questions regarding their work; and Ken Ramirez, Kay Laurence and Dr Susan Friedman for their inspirational teachings on animal behavior and training.
16 Further Reading
Murphy, J. and L. Anderson. (2019) Responsible Wind Power and Wildlife. Washington, DC: National Wildlife Federa- tion, National Audubon Society.
American Wind Wildlife Institute Report. (May 2019). Wind Turbine Interactions with Wildlife and Their Habitats, A summary of Research Results and Priority Questions.
Allison T. D. (November 2018). American Wind Wildlife Institute White Paper: Bats and Wind Energy: Impacts, Mitiga- tion, and Tradeoffs.
American Wind Wildlife Institute. (2017). National Wind Wildlife Research Plan 2018-2020. Washington, DC. Available at www.awwi.org.
Taber D. Allison, Jay E. Diffendorfer, Erin F. Baerwald, Julie A. Beston, David Drake, Amanda M. Hale, Cris D. Hein, Manuela M. Huso, Scott R. Loss, Jeffrey E. Lovich, M. Dale Strickland, Kathryn A. Williams, Virginia L. Winder. (Fall 2019). Ecological Society of America Report: Impacts to Wildlife of Wind Energy Siting and Operation in the United States, Report No. 21.
U.S. Fish and Wildlife Service. (September 2019). Indiana Bat 5-Year Review: Summary and Evaluation, Indiana Eco- logical Services Field Office Bloomington, Indiana.
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