Appendix G: Bats

G.1 Introduction

This chapter of the RWSC Science Plan addresses bat research and associated scientific needs in the context of offshore wind development. The plan is intended to reflect the research and data collection needs of RWSC’s four Sectors with input from the science community. The plan will provide a path forward to ensure appropriate data collection protocols and standards are in place to support scientific research; this document can also provide a framework that can aid RWSC participants in coordinating and aligning funding to carry out necessary scientific activities.

This plan benefits greatly from the contributions of RWSC Bird and Bat Subcommittee members; researchers, managers, and other practitioners who joined Subcommittee calls; and the many scientists who conducted research or developed reference materials cited throughout this plan.

Following this introduction, the first section of the chapter discusses the geographic extent of the area considered within this chapter, the species of bats which occur within this geographic range, and a summary of primary sources of information about species’ distributions. The next section of this chapter discusses potential effects of offshore wind development on bat species. The following section summarizes common field research methods for the study of bats, with a focus on the offshore environment.  The subsequent section addresses the major research topics and questions relevant to bats in the context of offshore wind development. The remainder of the chapter addresses recommended science actions of value to the four sectors that make up RWSC (state and federal agencies, eNGOs, and the offshore wind industry), in the context of recent, ongoing, and pending scientific activities relevant to recommended actions.

G.2 Species

This chapter addresses bat (Class Mammalia, Order Chiroptera) species which could be at risk from offshore wind development occurring in the Northwest Atlantic within U.S. waters. For the purposes of this plan, the geographic area of interest comprises the Atlantic Coast of the United States, extending from Maine’s northern border with Canada south to the Florida Keys, and from coastal areas extending 200 nm east into the ocean, including state waters (3 nm from shore) and federal waters of the Outer Continental Shelf (3-200 nm). This area is referred to in this plan as the RWSC Study Area. While the focus of this plan is offshore impacts of offshore wind development, potential onshore impacts of offshore wind on bat species are also possible. For example, clearing of transmission line corridors could remove trees used by summer maternity colonies. Therefore, bat species which primarily or solely occur in the onshore environment along the Atlantic Coast are nevertheless included within the scope of this plan, although they are not the focus of this chapter.

G.2.1 Bat Species occurring in the Northwest Atlantic

There are 17 species of bat which commonly or occasionally occur within the 14 states of the U.S. Atlantic Coast (Table 1). They are all insectivorous species that belong to the family Vespertilionidae. Three additional species, the velvety free-tailed bat (Molossus molossus), big free-tailed bat (Nyctinomops macrotis), and the Virginia big-eared bat (Corynorhinus townsendii virginianus), are either only rarely encountered in the RWSC Study Area or are only found inland and are not likely to interact with coastal or offshore activities related to offshore wind.

Table 1. Bats regularly occurring in the 14 states of the RWSC Study Area. The state ESA column indicates the number of Atlantic Coast states in which the species is listed as state endangered, threatened, or of special concern. The SGCN column indicates the number of Atlantic Coast states in which the species is listed as a Species of Greatest Conservation Need.
Scientific Name Common Name Federal ESA Status IUCN Red List Status State ESA SGCN
Corynorhinus rafinesquii macrotis Rafinesque’s eastern big-eared bat Least Concern 3 5
Eptesicus fuscus big brown bat Least Concern 0 10
Eumops floridanus Florida bonneted bat Endangered Vulnerable 1 1
Lasionycteris noctivagans silver-haired bat Least Concern 1 12
Lasiurus borealis eastern red bat Least Concern 1 12
Lasiurus cinereus hoary bat In USFWS Workplan Least Concern 1 12
Lasiurus intermedius northern yellow bat Least Concern 2 4
Lasiurus seminolus Seminole bat Least Concern 0 3
Myotis austroriparius southeastern myotis Least Concern 2 6
Myotis grisescens gray bat Endangered Vulnerable 3 4
Myotis leibii eastern small-footed bat Endangered 8 13
Myotis lucifugus little brown bat Under Review Endangered 6 13
Myotis septentrionalis northern long-eared bat Endangered Near Threatened 10 13
Myotis sodalis Indiana bat Endangered Near Threatened 7 7
Nycticeius humeralis evening bat Least Concern 0 3
Perimyotis subflavus tri-colored bat proposed Endangered
(Sept 2022)		 Vulnerable 4 14
Tadarida brasiliensis Brazilian free-tailed bat Least Concern 0 1

For more information about the species in Table 1, see Bat Species Descriptions [forthcoming in 2024].

G.2.1.1 Regulatory Status

Currently four bat species that regularly occur in the RWSC Study Area are listed as Endangered under the federal Endangered Species Act (ESA), one is under review, and one has been proposed for listing as Endangered. In addition, the hoary bat has been added to the USFWS National Domestic Listing Workplan to undergo a status review at the discretion of the Service in FY2027 (USFWS, 2023). The ESA places strict limits on the import, export, sale, possession, transportation, or “take” of listed species, with “take” defined as “to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct.” (United States, 1983). The ESA also allows for the designation of critical habitat for a species and prohibits the destruction of that habitat.

In addition to federal regulations, most states have a state Endangered Species List, which offers its own protections.  Fourteen bat species are protected by state statutes in the 14 states of the RWSC Study Area.  Individual State Wildlife Action Plans also identify Species of Greatest Conservation Need (SGCN) which serve as foci for research and conservation efforts; all of the bat species that regularly occur along the Atlantic Coast are listed as SGCN in one or more states (USGS, 2023).

Hoary bats, silver-haired bats, and eastern red bats were designated as Endangered in 2023 by Canada’s Committee on the Status of Endangered Wildlife in Canada (COSEWIC) due to land-based wind energy impacts on these species (COSEWIC, 2023).

G.2.1.2 Focal Species

At least six bat species have been detected visually or acoustically over the waters of the Northwest Atlantic (Solick and Newman, 2021). The vast majority of detections identified to species were one of the three long-distance migratory tree bats (eastern red bat, hoary bat, silver-haired bat). Tricolored bats, big brown bats, and Myotis species have also been detected, albeit more rarely (Solick and Newman, 2021). Challenges in differentiating amongst species acoustically (Nocera et al., 2019) means that it can be difficult to positively determine which Myotis spp. are detected offshore.

While some scientific research methods will provide information about a variety of taxa (e.g., acoustic surveys), other research methods (e.g., tagging) provide species-specific data. In the offshore environment, the three long-distance migrants are the focal species of greatest interest for tagging efforts due to the greater likelihood of their exposure to offshore wind farms, as described above, as well as anticipated higher collision risk, based on fatalities at land-based wind farms (AWWI, 2020). Eastern red bats and hoary bats are of particular interest - eastern red bats because they are detected most frequently offshore, and hoary bats because they are the species considered at greatest risk from land-based wind development (AWWI, 2020; Friedenberg and Frick, 2021). Land-based wind fatalities would suggest these species are most at risk during the late summer-fall migration season (Lloyd et al., 2023), and offshore acoustic data support the idea that migratory bats are most common offshore during this season (Stantec, 2016). For Perimyotis subflavus and Myotis species of conservation concern (see Table 1), tagging of individuals occurring in coastal areas and on islands is also of interest, particularly during the late summer and early fall, when they may make longer-distance movements to hibernation sites, which could involve over-ocean travel. Spring migratory movements from hibernation sites could also involve over-ocean travel, although it could be more difficult to target for tagging individuals headed for coastal and island summer territories if captured at inland hibernation sites. Northern long-eared bats, little brown bats, and tricolored bats have been successfully captured at coastal and/or island locations (Dowling, 2018; Grider et al., 2016; Hoff, n.d.; Zara Dowling et al., 2017); if other listed Myotis species are captured, they could also be considered potential focal species. At present, there are not identified sites where other Myotis could be captured in numbers large enough to represent a meaningful sample size.

Other species could be affected if near-shore facilities are built in the future, or by tree clearing and construction where transmission cables come ashore. In these circumstances, federally listed and state-listed species would be of greatest concern during the development process.

G.2.2 Regional Coastal/Offshore Distribution Information

Patterns of bat distribution and abundance in the offshore environment are poorly understood. Limited tagging/tracking efforts (Dowling, 2018; True et al., 2023) (T. Peterson, personal communication) and a number of mobile and stationary acoustic surveys have been conducted, in addition to documentation of incidental visual observations during aerial and boat-based surveys for other taxa (Hatch et al., 2013). Studies conducted through 2021 were summarized in a recent literature review (Solick and Newman, 2021), which provides a thorough compilation as well as links to the various studies included in the review. For more recent studies (since 2021), see the Tethys Knowledge Base and the RWSC Offshore Wind & Wildlife Research Database.

The North American Bat Monitoring Program (NABat) provides seasonal occupancy and abundance maps for a number of bat species across the U.S., modelled based on data collected by a host of federal researchers and other collaborators. Because the data are sparse, these maps do not yet include the offshore environment. However, the NABat grid system has been extended offshore, and the database is prepared to collect coastal and offshore detections of bat species, which can be incorporated into future analyses and mapping of species distributions (Cox et al., 2022).

Critical habitat for ESA-listed bat species, where designated, typically focuses on important hibernation sites or large summer maternity colonies. These could be relevant to onshore locations of transmission infrastructure for interconnection between offshore facilities and the electricity grid. Critical habitat designations for bats are available as part of USFWS species profiles, as follows:

G.3 Potential Effects of Offshore Wind on Bats

Collision with operating wind turbines is expected to be the main potential impact of offshore wind development on bats (NREL and PNNL, 2022), although collision risk and fatality rates in the offshore environment are currently entirely unknown. In the terrestrial environment, bat mortality at wind facilities is a common occurrence (AWWI, 2020), and these fatalities are estimated to represent a population-level, and even existential, threat to some migratory tree bat species (Frick et al., 2017; Friedenberg and Frick, 2021). Analyses of onshore rates of fatality at land-based wind facilities has suggested that wind-associated mortality could also compound population-level impacts to bat populations already affected by white-nose syndrome (WNS) (Erickson et al., 2016).

Overall, in the absence of offshore infrastructure, bat activity is thought to be lower at isolated offshore sites compared to most coastal, island, and inland habitats (Solick and Newman, 2021; Stantec, 2016). However, bats appear to be attracted to land-based wind turbines and other tall structures (Cryan et al., 2014; Guest et al., 2022; Jameson and Willis, 2014). Researchers have hypothesized that the greater height of offshore wind turbines and their prominence in an otherwise flat seascape could increase attraction of bats to offshore wind facilities (Solick and Newman, 2021), potentially increasing collision risk or leading to greater exposure to harsh weather conditions offshore (Wilson et al., 2023). Historic records indicate that bats sometimes flocked around sailing ships (Pelletier et al., 2013), and more recent studies have documented bats roosting and foraging around offshore turbines in Europe (Ahlén et al., 2009).

Given bat attraction to turbines, offshore wind facilities are not expected to cause habitat displacement or impose barriers to habitat connectivity. Offshore wind turbines in fact could offer potential roost and stopover sites or foraging locations for migrating bats (Ahlén et al., 2009; Brabant et al., 2020; Lagerveld et al., 2020), but due to collision risk, any energetic advantage conveyed by this increase in roosting habitat is likely more than offset by the potential negative impact of fatalities (Solick and Newman, 2021).

As noted above, the three migratory tree bats (hoary bat, eastern red bat, and silver-haired bat) have been found to be the most vulnerable to collisions at land-based wind facilities and are also the species that most commonly occur offshore. Therefore, these species are considered at the greatest risk of negative impacts. Little is known about the scale of potential impacts offshore on migratory tree bats or other bat species.

Potential positive effects of offshore wind development on bats are difficult to evaluate at present. The expected effects of climate change on North American bats are largely unknown (Hammerson et al., 2017), and thus climate change mitigation effects of offshore wind development are difficult to assess. Much of the literature regarding effects of climate change on bats comes from modelling studies rather than empirical evidence (Festa et al., 2023). In the U.S., mitigation measures are typically designed to offset losses due to new infrastructure, rather than provide a net benefit to species. However, through off-site mitigation, offshore wind facility operators could voluntarily choose to support conservation actions that could potentially provide a net benefit to bat species. For rare Myotis species, off-site mitigation strategies include protection of hibernacula and summer maternity habitat (USFWS, 2022). Effective methods for off-site mitigation for migratory tree bats have not been demonstrated. One benefit of offshore wind development to bats could be the greater scientific interest and research focus on these under-studied organisms; this might lead to a better scientific understanding that ultimately better serves these species.

G.4 Common Data Collection Methods and Approaches

A number of scientific methods are used for studying bats in the offshore environment, which are summarized below.  This section is intended to provide a brief description of different study methods, rather than a detailed assessment of the pros/cons and current state of development of each technology/methodology. For tracking of new technologies, see the Tethys database of monitoring technologies.

Note also that this brief review focuses on technologies or methods relevant to marine environments. There are additional survey techniques and protocols used in the terrestrial environment. Those are relevant to the study of terrestrial effects of offshore wind – such as effects of clearing transmission corridors to connect offshore wind with onshore grid infrastructure – but for the sake of brevity and a focus on novel offshore issues, they are not addressed here.

G.4.1 Acoustic Surveys

Acoustic surveys can be conducted using acoustic detectors to record calls of bats (Loeb et al., 2015). Surveys may be conducted using passive (stationary) methods or active methods. Active surveys onshore are typically conducted using a vehicle; at sea, they are often boat-based (Sjollema et al., 2014), although drones are beginning to be used experimentally (Workboat Staff, 2023). Passive surveys offshore utilize stationary detectors deployed on ocean buoys, meteorological towers, offshore wind turbines, other offshore infrastructure (such as electrical service platforms or “ESPs”); use of coastal and island sites are also common for understanding timing and locations of bat movements in the coastal and marine environments (Peterson et al., 2014). Acoustic surveys for bats utilize detectors which operate in the ultrasonic range in which most echolocation calls fall. Note that acoustic surveys are only effective when study animals are vocalizing, and ultrasound does not travel far through the atmosphere. Ambient noise can also interfere with detection of vocalizing animals and limit the distance over which calls will be recorded. Differentiating among species can also be difficult for certain taxa (Nocera et al., 2019).

G.4.2 Tagging and Tracking

Tagging and tracking can be a useful way to understand bat movements and activity. VHF (Very High Frequency) and UHF (Ultra High Frequency) radiotags transmit signals in the radio frequency range, which can be detected with a receiver. These types of tags are regularly deployed on bats. Historically, tags with different frequencies were deployed on animals within one research study to allow for easy identification of different individuals. The animals were then tracked, often via manual telemetry with a hand-held receiver. Manual tracking could be conducted on foot, or using a vehicle or aircraft. Study animals could also be tracked via a receiver attached to a stationary tower with antennae pointed in multiple directions, which could be automated to detect signals periodically or rotated manually by a researcher to detect a signal with an associated bearing. Manual telemetry is limited by the search effort available for finding and pinpointing the radio signal, and hence faces significant challenges in tracking animals that range over long distances.

In recent years, the development of the Motus network has allowed for much more widespread use of coordinated automated radiotelemetry for tracking of wide-ranging and/or migrating bats. This system relies on coded radio transmitters which all operate on one of two common frequencies, but which emit unique ID codes to identify different individuals. Signals from the tags are received by a network of automated radiotelemetry stations consisting of antennas, a receiver, a power source, memory storage, and sometimes data transmission infrastructure. Telemetry stations can be deployed on land, on coastal locations, or on offshore infrastructure, including ocean buoys and offshore wind turbine platforms. Advantages of this system include that tags are small and stations deployed by one research group can detect passage of animals by other researchers operating in the same network, allowing for development of a widespread network with more likelihood of detecting wide-ranging study animals. This system also has the distinct advantage over manual telemetry that signals can be monitored for continuously. Motus system technology has limitations, including limited range of some telemetry stations (typically 15 km) and, in most cases, an ability to determine only general proximity or bearing from the station rather than precise location. Efforts to improve triangulation capabilities are underway. Offshore wind developers are including deployment and maintenance of Motus stations as part of wildlife monitoring plans developed for review by BOEM and USFWS. While these stations are being deployed primarily to support avian studies, they can also benefit bats. Motus stations in the U.S. Atlantic are coordinated through the Atlantic Offshore Motus Project.

Tag battery life and retention on the bat can be limited, reducing the length of time that individual bats are successfully tracked via this system.

At present, other types of tags, including geolocators, GPS dataloggers, and satellite tags are not regularly deployed on bats in the RWSC Study Area. Satellite tags are currently too heavy to be placed on the bat species that occur along the Atlantic Coast of the United States. GPS dataloggers are only practicable for species that regularly return to the same roost, where the animal can be recaptured. They have been used in studies of the Florida bonneted bat (Webb, 2018), one of the largest bats on the Atlantic Coast, but other species are not as large or not as predictable in roost location. Geolocators require exposure to daylight to function, which is not necessarily available in bat roosts.

G.4.3 Banding and PIT Tags

Capture-mark-recapture studies can be used to assess longevity and survival of bats. While bird banding is a very common practice for birds of all sizes, bat banding is less common. Banding of bats (on the forearm, rather than the leg) is carried out by some researchers, but there are concerns that this practice could result in injuries to the animal (Lobato-Bailón et al., 2023). The USFWS has convened a working group to study this issue in bats and come up with recommendations. PIT (passive integrated transponder) tags are also used on bats in some instances and have good retention rates (Van Harten et al., 2021). These tags are implanted into the animal using an injector. These types of identification systems are most useful in situations where an animal is expected to return to a given site where it may be easily captured, such as maternity colonies or hibernacula.

G.4.4 Bat-Turbine Interaction & Collision Detection Systems

On turbine platforms, turbine nacelles, or other offshore infrastructure, cameras can be used to record bat presence and behavior in the vicinity of turbines, which can inform when and where animals are present in portions of the rotor-swept zone and document bat interactions with turbines, including roosting, attraction, micro-avoidance, lack of response, or collisions. Cameras differ in their mode of action, resolution, and the frequencies of electromagnetic radiation they use, from conventional cameras that operate in the visual range, to so-called “infrared” cameras that operate in the near infrared range, to so-called “thermal” cameras that operate in the far infrared range. The information provided by continuously operating cameras is unique and of great value to bat-offshore wind research. However, many of these systems are expensive at present and often only deployed at one or a few turbines in a study area. The field of view of a particular camera is often not sufficient to encompass the full rotor-swept zone. The extent to which these technologies can be counted upon to operate continuously in the harsh offshore environment is currently being evaluated.

At onshore wind facilities, carcass surveys are commonly used to document mortality and estimate fatality rates for a variety of bat species that collide with wind turbines. Offshore, carcasses of individuals can be expected to fall into the ocean in most instances and so collision detection systems are needed. Collision detection systems may incorporate visual range, thermal, or infrared cameras as described above (happ2021a?), as well as acoustic detectors, radar systems, and/or accelerometers for impact detection. Over a dozen multi-sensor systems for documenting collisions and other bat interactions with wind turbines are under evaluation or currently in use at wind facilities (Dirksen, 2017; NREL and PNNL, 2022), and at least three have been deployed on offshore turbines (Lagerveld et al., 2020; Mark Desholm, 2003; Tjørnløv et al., 2023; Willmott et al., 2023). Efforts are currently underway at land-based wind facilities to develop, improve, and validate collision monitoring technologies. At present, validation activities are limited to the terrestrial environment, where results can be compared with carcass searches. The development of new and emerging technologies in this category can be tracked using the Wind Energy Monitoring and Mitigation Technologies Tool.

G.4.5 Tissue Sampling

There are a range of tissue sampling methods from live-caught bats, or their feces, which provide a variety of information about individuals’ migratory status, diet, and health, as well as population-level genetic structure. These can include collections of blood, hair, wing membrane, and fecal matter, to variously conduct stable isotope analysis, physiological analyses, diet assays, detection of Pseudogymnoascus destructans (the fungus responsible for WNS), genetic analyses, or others.

G.4.6 Incidental Observations

Incidental observations can also provide useful information about species presence and behavior, particularly for bats, which are infrequently observed at sea. These observations have in some cases been collected via literature review (Pelletier et al., 2013). At-sea aerial and boat-based surveys for seabirds have in some cases recorded bat activity offshore on an incidental basis (Hatch et al., 2013).

G.5 Research Themes: Bats and Offshore Wind in the U.S. Atlantic

Research needs for offshore wind development and bats are centered around two common themes. First, there is a need to measure, estimate, model, or otherwise assess the scale of impacts of offshore wind development on bats, in order to determine whether impacts are significant at a subpopulation or population scale. Second, there is a need to understand how to address any impacts that may occur via effective mitigation. In the context of this chapter, “mitigation” is used broadly, as defined by the Council on Environmental Quality (CEQ) National Environmental Policy Act (NEPA) regulations. Thus, mitigation in this context includes:

  • Avoiding the impact altogether by not taking a certain action or parts of an action. This could include siting wind facilities in areas expected to have low bat activity (USFWS, 2012). However, post-construction mortality is not strongly correlated with pre-construction bat activity (Hein et al., 2013). If bat activity decreases with distance from the coast, siting turbines further from shore could be an avoidance strategy, but not enough is known at this time to determine where to site offshore wind facilities to reduce impacts to bats.

  • Minimizing impacts. This could include curtailing wind turbine operations during periods of high bat activity (e.g., low wind speed nights) so as to reduce the risk of collision fatalities, a practice determined to be effective at land-based wind facilities (Adams et al., 2021; Whitby et al., 2021). Minimizing the impacts on-site could also include use of deterrent technologies, if deemed effective. These technologies continue to be developed and evaluated at land-based wind facilities (Hein and Straw, 2021). In some studies, individual technologies have reduced overall bat fatalities (Hein and Straw, 2021; Romano et al., 2019; Schirmacher, 2020; Weaver et al., 2020); however, no deterrent has shown consistent reductions in fatalities of eastern red bats, the most commonly detected species offshore (Solick and Newman, 2021).

  • Rectifying the impact by repairing, rehabilitating, or restoring the affected environment. For example, this could include placing artificial roosting habitats (Mering and Chambers, 2014) or creating snags in areas where maternity roost trees were cut to make way for a transmission corridor.

  • Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action.

  • Compensating for the impact off-site. For example, this could include preserving foraging habitat, maternity roost sites, or hibernacula. As stated above, effective off-site compensatory mitigation techniques for migratory tree bat mortality have not been evaluated.

The goal of mitigation measures could be to meet regulatory requirements to negate or offset any negative impacts of offshore wind development, or to meet voluntary goals of providing a net benefit to the species.

From the perspective of a regulator, conservationist, or offshore wind developer, the progress of research would ideally proceed from development of accurate and cost-effective technologies for wildlife monitoring, standardized systems for data collection and analysis, and understanding of baseline conditions, moving then to evaluation of impacts and mitigation strategies, and finally to widespread development of offshore wind in the context of implementation of effective mitigation measures. However, given the rapid pace of offshore wind development (U. S. Department of Energy, 2023), this slow and measured progression is not a realistic timeline. Rather, multiple areas of research will need to be advanced simultaneously. In the meantime, regulators must necessarily rely on the best available science in assessing potential risks to protected and vulnerable species. Tools must continue to be developed to help inform these efforts. While many conservationists prefer focusing on earlier steps in the mitigation hierarchy (Arlidge et al., 2018), such as avoidance, the reality is that the impacts of offshore wind development will not be fully evaluated until many hundreds of turbines are installed. This suggests that effective on-site and off-site mitigation measures will also need to be an early focus, because once turbines are in the water, they are unlikely to be removed or fully turned off. On-site mitigation may be the most viable strategy for conserving migratory tree bats.

Given this context, important science and research topics related to bats and offshore wind development include the following:

  • Developing structures and methods to effectively and collaboratively conduct and share scientific research. This includes coordination, planning, collaboration, the standardization of data workflows, and development of improved data collection and dissemination methods.

  • Understanding baseline conditions of bat occurrence, activity, and movements offshore. This includes assessing species occurrence and relative activity of bats over different areas of the ocean, with particular attention towards whether relative bat activity declines over a gradient from coastal to offshore areas. This also includes documenting characteristics of offshore flights, including timing (time of year, time of night), relationships to meteorological conditions, flight speed, and differences across species, sexes, or ages. These types of data have the potential to inform mitigation efforts. Because of the rapid pace of wind development compared to the pace of data collection, and because it is possible that attraction will lead bats to visit offshore lease areas more frequently once turbines are installed, near-term siting decisions are unlikely to be made based on collection of baseline data.

  • Determining if patterns of bat occurrence, activity, and movements change after construction of offshore wind facilities. This includes continuing surveys of bat occurrence and activity post-construction to understand if patterns change and continuing to document characteristics of offshore flights. Post-construction studies of this kind may help elucidate whether, and to what degree, attraction to turbines is occurring, and whether siting could be an effective mitigation strategy for future wind projects.

  • Assessing collision risk at offshore facilities. Until validated and effective collision detection methods are widely available, proxies are necessary to assess collision risk. For bats, acoustic activity, particularly recorded at nacelle height in conjunction with information regarding turbine operational status, may be the best indicator of potential collision risk (Peterson et al., 2021). Assessing bat activity at turbine nacelle height relative to timing, meteorological conditions, turbine characteristics, turbine operational status, and species is an important research goal. (Tracking data may also provide information about movements of non-echolocating bats.) Turbine-mounted cameras and multi-sensor collision detection technologies may be able to provide actual measures of collision risk and fatalities. These data can help in understanding the relative risks to bat populations posed by collisions offshore as compared to fatalities at land-based wind facilities and other threats.

  • Designing and evaluating on-site minimization strategies. Assessments of the conditions associated with heightened collision risk (previous bullet) can inform design of efficient, “smart” curtailment strategies for bats, if these methods are deemed necessary to avoid population-level impacts to bats. If determined to be effective in the terrestrial environment, deterrents could also be tested offshore.

  • Evaluating off-site compensatory mitigation strategies. If on-site mitigation measures are deemed insufficient or are cost-prohibitive, off-site mitigation measures could be considered.  However, these measures would need to be evaluated carefully to determine if they are realistic and adequate to address negative impacts.

A database of specific research questions related to bats and offshore wind is available through the U.S. Atlantic Offshore Wind Environmental Research Recommendations Database.