Wind, sun, and wildlife: do wind and solar energy development 'short-circuit' conservation in the western United States?

Our search returned 232 journal articles concerning renewable energy (wind and solar) and wildlife in North America from 2010–2018 (table 1). The number of journal articles published each year varied over time from nine in 2010 to 24 in 2018 and peaked in 2013 with 39 publications. Journal articles were predominantly empirical research studies (68%) and focused on the effects of wind energy (72%) with an ecological focus (57%) and volant species assessment (54%) (table 1, figure 1). The least studied subcategory included the species group aquatic taxa (1%) (table 1). These results are similar to the findings produced in previous reviews, such that relatively little has been published regarding non-volant wildlife species (Lovich and Ennen 2011, 2013). Nonetheless, our results show an increased focus on environmental impacts resulting from renewable energy development over the past decade, as a previous review conducted in 2005 noted that only 4% of all publications on the topic covered ecological impacts (Gill 2005). Evaluating empirical studies only from 2010–2018, the total number (i.e. count) of studies that focused on renewable energy development increased with year, the total number of studies that focused on renewable energy design was positively correlated with the total number of studies focused on volant species, wind and offshore wind technology; and the total number of studies that focused on renewable energy siting was positively correlated with topics including wind energy technology (figure 2). The geographic distribution of studies produced in our review reflects a strong focus on the western US. As such, wildlife impacts in California were a primary target for 17% of the research studies reviewed, followed by Texas (5.5%) and Wyoming (4%). These results may reflect the accelerated growth and potential of renewable energy development in the American West, and that most of the installed or planned utility-scale facilities are located in states such as California, Arizona, and Texas.

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Our literature review revealed that 13% of journal articles mentioned or focused on the importance of renewable energy siting or facility design. This figure is surprisingly low. As pointed out by Arnett and May (2016) in their review of how to mitigate the effects of wind energy on various animals, avoidance of predicted high risk areas is the logical first step of effective mitigation. The same tenet applies to solar energy development. Selecting the optimal location for the footprint of the facility is paramount for minimizing negative impacts on sensitive species and habitats. Examples of sensitive areas for wildlife include: core habitats (e.g. winter or summer range for ungulate populations like Mule Deer (Odocoileus hemionus), Webb et al 2013); lekking areas for Prairie Chickens (Tympanuchus cupido) (Smith et al 2016); riparian areas, especially in the arid western US (Grippo et al 2015); and along migratory corridors (e.g. Johnston et al 2014).

Alternative locations that have little or no impact on wildlife include built or already disturbed environments, as exemplified by roof-top solar in urban areas, that confer environmental co‐benefits including conserving wildlands (Moore-O'Leary et al 2017, Assouline et al 2017), and recommendations to direct future development of wind energy toward already disturbed lands in the US (Kiesecker et al 2011). However, large-scale deployment at these locations may have wider reaching implications that affect wildlife and their habitat (Millstein and Menon Millstein and Menon 2011) far beyond. Other locations with substantially reduced or eliminated negative effects on wildlife include brownfields, like contaminated industrial sites (Adelaja et al 2010, Stoms et al 2013) and agricultural areas (e.g. Barron-Gafford et al 2019). Redevelopment of such sites for energy production can result in substantial economic benefits to local communities as well. Grassy areas around airports can also be used for solar energy development (Devault et al 2012) as one of the few areas where reductions in wildlife abundance and habitat quality are necessary and socially acceptable, to reduce wildlife collisions with aircraft. Since 2010, there has been little evidence of a reduced emphasis on the development of utility-scale solar energy in wildlands (particularly shrublands) of the southwestern US, as illustrated by the situation in California (Hernandez et al 2015a). Parker et al (2018) found that solar development in the Mojave Desert as of about 2010 had a footprint of 86.79 km²: 25.81 km² (29.7%) of this was primarily high conservation value public lands in Ivanpah Valley, and 60.99 km² (70.3%) was privately owned lands, mostly of lower conservation value, in the western portion of the Mojave Desert.

As reviewed by Arnett and May (2016), a number of tools are available to the renewable energy sector to make informed decisions on renewable energy site selection, including minimizing or eliminating negative impacts to wildlife. Included are detailed maps maintained by state resource management agencies and conservation organizations showing the distribution of sensitive wildlife and their habitats. Another option is to use various models of species occurrence and diversity as was done by Thomas et al (2018) for wind and solar energy in Arizona, USA. The premise in this analysis is that areas that have high biodiversity or concentrations of sensitive species should be avoided. The availability of publicly accessible vertebrate habitat models for the entire US adds to the value of this technique. Others have examined the occurrence of high genetic diversity and connectivity in the western US (Vandergast et al 2013, Wood et al 2013) to identify areas of high conservation value relative to siting solar projects.

In contrast to what most authors conclude about site selection, other studies suggest that '...responsibly developed solar power plants can provide shelter, protection, and stable use of land to support biodiversity' (Sinha et al 2018), using the Topaz Solar Farms Project in southern California as an example. During post-construction surveys, the authors documented similar or increased vegetative productivity compared to reference sites. They also documented continued occupancy of sensitive wildlife species. One of those species is the federally-endangered San Joaquin Kit Fox (Vulpes macrotis mutica). By working with biologists, project managers developed and installed a fence that allowed passage of Kit Foxes but prevented adult Coyotes (Canis latrans), a predator of the former, from entering the facility, thus providing a level of protection to Kit Foxes (Cyper B 2019 Personal Communication).

BACI designed studies are considered to be the 'optimal impact study design' (Green and Green 1979), and the preferred method to determine displacement of wildlife by energy development (Strickland et al 2011). Despite the known benefits of the BACI design (i.e. strong management inferences, mitigation strategies for future development), these types of studies are difficult to conduct as they require prior knowledge of site selection by developers and long-term data and funding to match timing of development. Unsurprisingly, BACI studies that evaluate impacts on wildlife remain rare, similar to the findings of Lovich and Ennen (2011, 2013) for renewable energy development and operation nearly ten years prior to our study.

Our present review identified only five studies (2%) that mention BACI as a necessary analysis for understanding the relative effects of renewable energy development on wildlife. Of those five studies, three studies conducted a BACI analysis in the US (Mcnew et al 2014, Shaffer and Buhl 2016, Lebeau et al 2017). These investigations performed a BACI assessment to determine whether wind facilities placed in prime wildlife habitat affect survival of displaced bird species and their associated nesting habitats. Use of BACI in these research efforts provided potential avenues for mitigating impact of energy development (Mcnew et al 2014), and metrics to facilitate future development models for evaluating impacts of renewable energy facilities under differing land-use scenarios. While BACI-design studies are difficult to conduct, they remain an important approach for understanding how we can mitigate environmental impacts and improve site selection and design of future utility-scale renewable energy developments. Without more BACI studies, our knowledge is severely restricted in understanding the true impacts of these facilities on wildlife.

The mitigation hierarchy is avoidance, minimization, and compensation (Arnett and May 2016), or restoration (Kiesecker et al 2010). However, there is no 'silver bullet' solution along the mitigation pathway to protect all species from impacts of renewable energy facility development and operation, except total avoidance. In short, all energy sources will come with a cost to some wildlife, and each particular mitigation technique and strategy is usually species-biased, site-specific (Moore-O'Leary et al 2017), and will not cover the entire wildlife community being affected.

The best mitigation strategy is to avoid developing sensitive and pristine areas, which can be assessed in the pre-construction phase to identify issues related to wildlife, especially sensitive and threatened species (Arnett and May 2016; see above). Most of the known mitigation literature—in particular, solar energy-related literature—focuses on spatial planning and avoiding sensitive areas (Cameron et al 2012, Stoms et al 2013, Hernandez et al 2015a, 2015b, Kreitler et al 2015, Arnett and May 2016; see above), and less so on minimization or compensation strategies.

However, there has been progress in minimizing impacts from existing renewable energy facilities, especially wind energy, but not necessarily for solar energy. For example, studies have reported positive results—reduced mortality—for repowering wind turbines (Smallwood and Karas 2009), using automated monitoring (Mcclure et al 2018), sensors (Hu et al 2018) and acoustic deterrents (Arnett et al 2013), and adjusting operation times (Singh et al 2015) and cut-in speeds (Barrios and Rodriguez 2004, Smallwood et al 2009, Arnett et al 2011). However, for many of these mitigation strategies, there are published studies with conflicting results, suggesting that success is highly variable and site-specific (Arnett and May 2016). Thus, use of BACI studies may improve our understanding of how these mitigation strategies could be improved and how alternative facility designs may continue to evolve.

Finally, offsite compensatory mitigation is a 'last resort' strategy that includes land acquisition, preservation, and restoration of offsite habitats (Hartmann and White 2019). These actions are rare for wind and solar energy developments (Arnett and May 2016, Hartsmann and White 2019), but were, at one point, required under various federal laws (e.g. Clean Water Act and Endangered Species Act [ESA]; Hartmann and White 2019). However, the federal requirement of compensatory mitigation was rescinded in March 2017 by an Executive Order and federal agencies need not require compensatory mitigation for project approval (Hartmann and White 2019). Now, compensatory mitigation as a requirement for project approvals falls within state jurisdiction (Hartmann and White 2019).

As previously noted, the desert Southwest US is a hotspot for renewable energy development (Bachelet et al 2016). Despite its appearance as a rugged and timeless landscape, this arid region is sensitive to disturbance and recovers very slowly from anthropogenic disturbances (Lovich and Bainbridge 1999), including renewable energy development (Hernandez et al 2014, 2015a). It is also home to a surprisingly diverse group of animals that are affected by both solar and wind energy development and operation (Lovich and Ennen 2011, 2013). Included are federally protected, conservation-reliant species like the two species of desert tortoises (Gopherus agassizii and G. morafkai) and greater sage-grouse (Centrocercus urophasianus), all of which are threatened by renewable energy development.

Greater sage-grouse and desert tortoises receive a great deal of state- and federal-level conservation attention due to their declines and sensitivity to habitat loss. Both taxa are considered indicator or umbrella species due to their interaction with a myriad of species including other federally listed species, and are sensitive to changes in the environment (Grodsky et al 2017, Lebeau et al 2017a, Pilliod et al 2020). As an ecosystem engineer, Agassiz's desert tortoises provide habitat for many animals that cohabitate burrows like rodents, snakes, lizards, mesocarnivores, and ground birds including burrowing owls (Athene cunicularia) (Agha et al 2017); it also shares similar habitat to that of the federally threatened Mohave ground squirrel (Xerospermophilus mohavensis) (Logan 2016). As a wide-ranging sagebrush prairie-grassland species, greater sage-grouse co-occur with a host of other similar volant species that occupy the same habitat in the western US, including the golden eagle (Centrocercus urophasianus)—a species also considered to be ecologically important and affected by renewable energy development (Lovich 2015, Tack et al 2020).

Solar energy development in desert tortoise habitat is a significant concern for recovery of the species (Lovich and Ennen 2011). Prior to the listing of the desert tortoise under the ESA in 1990, renewable energy development was a minor contributor to habitat destruction of tortoises around the time of listing (Baxter and Stewart 1986, Pasqualetti 2001).With the recent buildout of utility-scale solar and wind facilities in the region, there is now concern that renewable energy development poses a substantial risk to tortoise populations, primarily through habitat destruction, fragmentation, and modification (Lovich and Ennen 2011, Averill-Murray et al 2012, Lovich et al 2018). To date, mitigation of solar energy development in tortoise habitat has relied almost exclusively on mitigation translocation (as opposed to conservation translocation, see Sullivan et al 2015) and/or head-starting. Although these sound like simple and logical solutions, these strategies have been criticized for various reasons, especially the fact that it has a low success rate for many reptiles and amphibians (Frazer 1992, Seigel and Dodd 2000, Germano and Bishop 2008, Sullivan et al 2015), including desert tortoises (Mack et al 2018). Nevertheless, the promise of success has led to renewed interest in both strategies for desert tortoises (Sadoit et al 2017, Dickson et al 2019, Tuberville et al 2019). Over five years post-translocation, desert tortoises displayed no adverse effects on condition, growth, or mortality (Sadoti et al 2017, Dickson et al 2019). Several noticeable short-term effects related to translocation include restricted movements caused by barrier fences (Sadoti et al 2017, Peaden et al 2017), higher average maximum daily shell temperatures (Brand et al 2016), larger home ranges (Fransworth et al 2015), and males siring fewer offspring (Mulder et al 2017).

Head-starting is another potential mitigation strategy for energy development in tortoise habitat (Tuberville et al 2019). This involves raising juvenile tortoises in captivity until they attain a size making them less susceptible to mortality from predation and other factors. Again, there is controversy in the scientific literature about the effectiveness and value of head-starting (Frazer 1992), including for desert tortoises (Mack et al 2018), but the promise of success has led to renewed interest in head-starting desert tortoises. Research is ongoing regarding how to enhance the success of juvenile tortoises after head-starting (Hazard and Morafka 2002, Hazard et al 2015, Nagy et al 2015a, 2015b, 2016, Daly et al 2018, Tuberville et al 2019). Notwithstanding the promising results suggested by short-term studies of translocation and head-starting of desert tortoises as mitigation strategies for renewable energy development, long-term data are yet unavailable for this long-lived species to conclude ultimate success.

Thus far, concerns about the negative effects of wind energy in the western US have focused mostly on mortality and habitat displacement for birds and bats (see recent review in Allison et al 2019), although some information is available for non-volant species (Lovich and Ennen 2013, Agha et al 2015, 2017). For instance, impacts of wind energy development and operation on desert tortoises increases mortality associated with road infrastructure (Lovich and Ennen 2011), facility infrastructure fire effects on habitat (Lovich et al 2018), and displacement over the long-term (Lovich and Ennen 2017).

Similar to desert tortoises, greater sage-grouse are threatened by a variety of anthropogenic- and ecosystem-based factors including natural resource extraction, land conversion for agriculture and development, invasive plant species, wildfires, and most recently wind energy development (Chambers et al 2017). Some studies have noted a negative effect of energy development on their survival, such that increased surface disturbance, noise, and habitat fragmentation can lead to lower nest and brood survival (Lebeau et al 2014, Kirol et al 2020). For instance, continuous monitoring of 95 nests and 31 broods at an operating wind energy facility in Wyoming, USA revealed that risk of nest and brood failure increased within habitats of proximity to wind turbines (Lebeau et al 2014). Additionally, LeBeau suggested that it is critical to identify nesting and brood-rearing habitat when evaluating potential impacts of wind energy development on overall population fitness (Lebeau et al 2014). Although the knowledge on impacts of wind energy on the greater sage-grouse is limited, there is plenty of information about the impacts of infrastructure associated with oil and gas developments that can guide managers (Kirol et al 2015, 2020). For example, yearlings exhibit avoidance behavior near energy infrastructure, lower survival reared within energy infrastructure, and less frequently establish breeding territories (Holloran et al 2010).

While populations of the greater sage-grouse presently appear stable in the western US, there is a growing concern surrounding the potential for decreased survival in the face of increased wind energy development in the western US (Lebeau et al 2014, 2017b). Resultingly, conservation managers have proposed a wide array of mitigation strategies that fall along all steps of the mitigation hierarchy (Johnson et al 2007). In terms of avoidance, planners have suggested placing areas off-limits to development, as 28% of developable land in Wyoming are in greater sage-grouse core areas (Jakle 2012). Wyoming State guidelines state that no wind energy development should occur within sage-grouse core areas, and that development should be at least 0.4 km from the perimeter of occupied leks outside of core areas (Lebeau et al 2017). For minimizing impacts, seasonal restrictions on construction activities could be imposed and site design could be modified (i.e. spacing of turbines). For instance, some studies recommend caution when designating buffer sizes <1.5 km to avoid measurable impacts from wind turbines on greater sage-grouse and their broods (Lebeau et al 2017). Furthermore, wind energy infrastructure such as powerlines may reduce habitat suitability and survival of greater sage-grouse, and thus minimizing design features that attract predators is warranted (Lebeau et al 2019). Finally, some wind projects have proposed compensatory mitigation—West Butte Wind Project in Oregon—which includes providing restoration and enhancement of over 9000 acres of greater sage-grouse habitat on BLM-administered land and providing funds to the country of conservation easement purchases for greater sage-grouse management (Jakle 2012). Wind energy facility design and compensatory mitigation may be successful, given that short-term impacts to greater sage-grouse have been variable based on recent studies (Lebeau et al 2014, 2017).