Wind Energy October 2009 overview
Summary of Wildlife and Habitat Threats
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- WILDLIFE AND HABITAT THREATS/RISKS
- EXAMINATION OF SOLUTIONS
- Mitigation Efforts and Strategies
Summary of Wildlife and Habitat ThreatsAs with other energy technologies, wind energy projects have impacts on the environment that should be addressed to minimize the effects. Installation and operation of wind facilities impact habitats, causing soil erosion and environmental degradation (Berry et al, 2005; Kuvlevsky et al, 2007). Access roads and noise from the turbines and traffic may cause species displacement and avoidance (Morrison and Sinclair, 2004; Berry et al, 2005; Drewitt and Langston, 2006; Madders and Whitfield, 2006; Kuvlevsky et al, 2007). Construction and operation of wind facilities may alternatively attract prey, such as insects and small mammals (Morrison and Sinclair, 2004; California Energy Commission, 2007; Kuvlevsky et al, 2007). Birds and bats are especially affected by wind energy projects. Birds are susceptible to wind facilities, especially passerines. Turbines placed along migration routes or foraging paths (often where the most favorable wind conditions are found) cause birds to be at high risk of collision and mortality (Morrison and Sinclair, 2004; Hoover and Morrison, 2005; California Energy Commission, 2007; Drewitt and Langston, 2008). Avoidance of facilities can also lead to an increased expenditure of energy during flight, which may also place birds at risk (Drewitt and Langston, 2006). Turbines spread out in a line are more hazardous to birds than those placed in clusters as they try to navigate their way through the turbines (Morrison and Sinclair, 2004; Kuvlevsky et al, 2007). Turbines with faster blade tip speeds are also more dangerous to birds since the blades essentially become invisible the closer they get to the turbine (Morrison and Sinclair, 2004; Kuvlevsky et al, 2007; Drewitt and Langston, 2008). Quantification of overall bird mortality due to anthropogenic factors is imprecise (National Research Council, 2007), however it has been estimated that between 100 million and 1 billion birds are killed annually by man-made structures. Wind energy facilities account for approximately 0.01% of this annual figure (Figure 4; Erickson et al, 2001), although quantification of impacts to species and populations is largely unknown (Longcore et al, 2005). 
Figure 4. Causes of Bird Fatalities, Number per 10,000 fatalities (Erikson et al, 2001). While birds are susceptible to wind facilities, mortality rates for bats are generally higher, especially for migratory foliage-roosting bat species (Barclay et al, 2007; Cryan and Brown, 2007; Kunz et al, 2007; National Research Council, 2007; Arnett et al, 2008). Most fatalities and injuries tend to occur predominantly during late-summer and fall migration (Arnett et al, 2007; Cryan and Brown, 2007; Kunz et al, 2007; Kuvlevsky et al, 2007; Marsh, 2007; Nicholls and Racey, 2007; National Research Council, 2007; Arnett et al, 2008; Cryan, 2008; Horn et al, 2008a,b) and may be related to foraging around turbines in response to variable abundance of insect prey. Foraging habitat for bats may be enhanced as a result of forest clearings created for turbine installation (Horn et al, 2008a). Collisions with spinning, rather than stationary blades suggests that bats either do not see the blades in time to avoid them (Barclay et al, 2007; Horn et al, 2008a; Arnett et al, 2008) or they become caught up in the vortex caused by the spinning blades and experience barotraumas (a rapid reduction of air pressure in the lungs), fatalities resulting from which have been documented at a wind facility in Canada (Baerwald, 2008). Summary of Solutions There are still several options wind energy developers can take to minimize or eliminate impacts. The most important is to avoid ecologically sensitive areas (Berry et al, 2005), as well as those areas used for migration and foraging flight paths (Drewitt and Langston, 2006; Drewitt and Langston, 2008). Many practices at turbine installations will need to be tailored to address site-specific and species-specific issues. The relationship between topography and weather patterns should be assessed prior to construction to determine if turbine placement would be too dangerous for birds (Hoover, 2005). Powering down turbines that are located at the top of slopes—where winds are favorable and raptors prefer to hunt—during times when strong winds blow perpendicular to the slope, will reduce raptor injuries and fatalities (Hoover, 2005; Drewitt and Langston, 2008). Turbine rows should be placed parallel to the flight path instead of across it (Drewitt and Langston, 2008), and spaced further apart to allow more room for birds to fly between the towers (Morrison and Sinclair, 2004; Marsh, 2007). An attempt at making the turbines and rotor blades more noticeable, such as a single black blade paired with two white blades (Morrison and Sinclair, 2004; Hoover, 2005) or adding a whistling effect to turbines (Dooling, 2002; Morrison and Sinclair, 2004) may help decrease the risk of collisions. Even though little is known about bats and their migration, foraging and roosting habits, mitigation options are still available to help minimize the risk of injury or death due to wind facilities. As with birds, ecologically sensitive areas (i.e. near open water sources or near known cave roosts) should be avoided (Arnett et al, 2008). Reduced tower heights (Barclay et al, 2007; Arnett et al, 2008) and the use of acoustic deterrents (Spanjer, 2006; Horn et al, 2008b) may help deter bats from flying or foraging around turbines. There is growing evidence that increasing the cut-in speed (i.e. the pre-set minimum wind speed at which the rotors beginning spinning) can dramatically reduce bat fatalities with minor impact on overall energy generated (Arnett et al, 2009). On nights of low wind speeds, the cessation of operations, especially during migration season, would help reduce fatalities (Marsh, 2007; Arnett et al, 2008; Horn et al, 2008a,b). WILDLIFE AND HABITAT THREATS/RISKSIntroductionDespite the number of positive aspects of wind energy, there are still concerns about the environmental impacts. Specifically, habitat fragmentation and degradation, collisions resulting in injuries and mortality of migrating birds and bats, as well as disturbance to other Species of Greatest Conservation Need, are all issues that developers and other stakeholders involved in wind energy projects need to address. Threats and Risks to Habitats Erecting a wind turbine can impact wildlife habitats. The amount of habitat disturbed during installation varies from one acre to three acres per turbine depending on the geographic location (National Research Council, 2007). Disruptions to habitats can occur due to construction that constitutes removal of vegetation from the area (Berry et al, 2005; Drewitt and Langston, 2006; Kuvlevsky et al, 2007). Access to the structures requires that roads be built. Transmission lines are also necessary to transport the generated energy. Above-ground electrical transmission lines can cause bird collisions and electrocutions, as well as cause erosion and environmental degradation (Berry et al, 2005; Kuvlevsky et al, 2007). The access roads may divide some forest-dwelling species by serving as barriers (National Research Council, 2007) and can increase mortality rates due to vehicle collisions (Kuvlevsky et al, 2007). When turbines become operational, habitat is lost throughout approximately 2% - 5% of the development area (0.2 - 0.5 acres) (Morrison and Sinclair, 2004; Drewitt and Langston, 2006; Kuvlevsky et al, 2007). Displacement can occur due to the noise, visual and vibration impacts from the turbines, and from the traffic patterns on the access roads (Drewitt and Langston, 2006; Madders and Whitfield, 2006; Kuvlevsky et al, 2007). Habitat avoidance is also a possibility as some birds and animals tend to avoid nesting or foraging in the vicinity of turbines (Morrison and Sinclair, 2004; Berry et al, 2005; Madders and Whitfield, 2006; Kuvlevsky et al, 2007). These disturbances can extend from 100 - 600 meters from a wind facility (Drewitt and Langston, 2006; National Research Council, 2007). Invasive plant species are often introduced at roadsides and may further fragment habitats and out-compete native species. Construction and operation activities may enhance habitat for insects and small mammals in the areas around turbines, attracting birds and other species which prey on them (Morrison and Sinclair, 2004; California Energy Commission, 2007; Kuvlevsky et al, 2007). Alteration of the vegetation around turbines may also influence bird and bat populations due to the changed landscape’s new population capacity and ability to accommodate prey species (National Research Council, 2007). Threats and Risks to Avian Species Currently, nationwide avian mortality due to collision with turbines is estimated at less than 0.01% of the total avian mortality rate (Johnson et al, 2002; de Lucas et al, 2008), or 2.19 birds/turbine/year, totaling approximately 33,000 birds/year (Erickson et al, 2001; Howe et al, 2002), most of which occur in California. Excluding California, there are approximately 6,400 bird fatalities per year due to terrestrial wind turbines (Erickson et al, 2001). Roughly 6% of bird fatalities consist of raptors (National Research Council, 2007). The majority (> 80%) of avian fatalities at wind sites appear to be passerines such as warblers (Parulidae) and sparrows (Passeridae), with 20% - 70% of these being nocturnal migrants (Johnson et al, 2002; Mabee et al, 2006; Kuvlevsky et at, 2007; National Research Council, 2007). The majority of collisions tend to occur during migration (Drewitt and Langston, 2008). Cumulative turbine mortality (i.e., from multiple wind sites as opposed to the small numbers of collisions at individual turbines) may be expected to have relatively fewer population impacts on passerines compared to other bird orders due to generally larger population size; however, turbine strikes and mortality may be detrimental to raptor populations due to their longevity and low reproductive rates (Morrison and Sinclair, 2004; Kuvlevsky et al, 2007; Newton, 2007). Flight Patterns. The correlation between flight behavior, topography and wind velocity appears to be the main reason leading to injury or death in raptors (Hoover, 2005; de Lucas et al, 2008). Collisions are more likely to happen if wind turbines are placed in the flight pathways used for migration, foraging, nesting or breeding (Morrison and Sinclair, 2004; Hoover, 2005; California Energy Commission, 2007; Drewitt and Langston, 2008). It has been suggested that turbines placed along mountain ridges or passes may experience higher collision rates due to the topography channeling migrating songbirds and raptors (Kuvlevsky et al, 2007; National Research Council, 2007; Drewitt and Langston, 2008), although broad-front migration patterns may be more prevalent in general (Mabee et al, 2006). Turbines placed on the edges of ridges, as well as those placed in gullies or valleys, have a high potential of collisions due to flight paths and the tendency of birds, especially raptors, to hover near ridgelines in order to use the favorable wind conditions for soaring during migrations and daily foraging (Morrison and Sinclair, 2004; National Research Council, 2007). Hoover (2005) observed during his study of red-tailed hawks (Buteo jamaicensis) in the Altamont Pass Wind Resource Area (APWRA) that the majority of deaths occurred on slopes where 90% of kiting activity occurred. Kiting (or motionless, flapless flight), a foraging technique favored by red-tailed hawks and other raptors during strong winds, may lead to possible injury or death due to sudden changes in wind velocity possibly throwing the bird off balance and into the turbine blades (Hoover, 2005). However, raptors and large birds with a low capability for powered flight, such as griffon vultures (Gyps fulvus), and poor maneuverability, are more vulnerable to collision due to their inability to rise above the turbines with a weaker uplift wind (de Lucas et al, 2008; Drewitt and Langston, 2006; Drewitt and Langston, 2008). Turbine collisions are more likely to occur with passerines, however, than with raptors because they migrate at night, usually below 600 meters (Mabee et al, 2006; National Research Council, 2007). Birds may even change their migratory or normal flight paths in order to avoid wind facilities, both onshore and offshore, leading to an increase in energy expenditure (Drewitt and Langston, 2006; Kuvlevsky et al, 2007). Weather conditions (e.g., fog, low clouds, high winds and storms) may also cause a bird to fly lower than normal during migration, leading to a possible increase in turbine strikes (Erickson et al, 2001; Johnson et al, 2002; Morrison and Sinclair, 2004; Berry et al, 2005; Drewitt and Langston, 2006; Madders and Whitfield, 2006; Newton, 2007; National Research Council, 2007; Drewitt and Langston, 2008). Structure and Lighting. The greatest number of collisions usually occurs at structures taller than 150 meters (Newton, 2007), none of which are currently operating in the US, and when turbines are spaced in a long line instead of in clusters due to birds trying to navigate their way through the gaps in the structures (Morrison and Sinclair, 2004; Kuvlevsky et al, 2007). Likewise, lattice towers may provide perching opportunities for birds (Smallwood and Neher, 2004; Thelander and Smallwood, 2004), thereby increasing the risk of collision. Artificial lighting (particularly constant burning lights) located on structures can cause birds to collide due to their attraction to artificial lights when the moon and stars are obscured (Johnson et al, 2002; Morrison and Sinclair, 2004; Berry et al, 2005; Drewitt and Langston, 2006; Drewitt and Langston, 2008; Gehring et al, 2009), although this has been little studied specifically at wind turbines. Studies of avian mortality at the Altamont Pass Wind Farm in California have provided information on turbine specifications and operations that pose risks to raptors. Turbines with larger rotor diameters, as well as lower blade reaches, are most hazardous to raptors, especially golden eagles (Aquila chrysaetos) (Thelander and Smallwood, 2004). The current created by the moving rotors may force birds to the ground (Drewitt and Langston, 2006; Drewitt and Langston, 2008). Intermediate or faster blade tip speeds appear to cause the most mortality as a result of “motion smear” (i.e., the blades are blurred and the bird cannot see them as easily) (Morrison and Sinclair, 2004; Kuvlevsky et al, 2007; Drewitt and Langston, 2008). Due to motion smear, a bird will usually hear a turbine before seeing it. However, because of their poor hearing range (they hear best between 1-5 kHz, less than the range of most mammals), by the time a bird can hear the turbine blades, it is usually too late for them to avoid the structure (Dooling, 2002). Animals, such as cattle, allowed to roam freely may also indirectly contribute to bird collisions. When cattle are allowed to graze near turbines, their dung attracts insects which then attracts smaller raptors, such as the American kestrel (Falco sparverius) and burrowing owl (Athene cunicularia), increasing the collision risk (Drewitt and Langston, 2008). Rock piles strewn around the bases of turbines tend to attract small animals, such as rabbits and gophers, which raptors prey upon, subsequently increasing the risk of collision (Morrison and Sinclair, 2004; Thelander and Smallwood, 2004; Drewitt and Langston, 2008).
At some projects, wind turbine mortality rates are estimated to be much higher for bats than for birds, indicating a greater potential for decreases in bat populations (Kuvlevsky et al, 2007). It has been estimated that up to 70 bats/turbine/year are killed worldwide (Cryan, 2008). Over 78% of bats killed at wind energy facilities are migratory tree bats (Cryan and Brown, 2007; Kuvlevsky et al, 2007; National Research Council, 2007; Cryan, 2008; Horn et al, 2008a); breeding bats localized to the area appear to mostly avoid turbines (Johnson et al, 2004). Eleven of the 45 bat species known to be present in the United States have been killed or injured at wind facilities. Migratory foliage-roosting bat species appear to be the most at risk, including the hoary bat (Lasiurus cinereus), the species having the highest proportion of fatalities at most sites (Arnett et al, 2008). Other species include the eastern red bat (Lasiurus borealis), eastern pipestrelle (Pipistrelles subflavus), little brown myotis (Myotis lucifugus), silver-haired bat (Lasionycteris noctivagans), big brown bat (Eptesicus fuscus), northern long-eared myotis (Myotis septentrionalis) and, to a lesser extent, Seminole bat (Lasiurus seminolus) (Barclay et al, 2007; Cryan and Brown, 2007; Kunz et al, 2007; National Research Council, 2007; Arnett et al, 2008). It has been estimated that an average of 3.4 bats/turbine/year collide with turbines, ranging from 1.2 bats/turbine/year in the northwestern United States to 46.3 bats/turbine/year in the eastern United States (Kuvlevsky et al, 2007). Bat fatalities are more prevalent in the eastern United States where wind facilities are located along forested ridges; fatality rates at the highest risk locations range from 15.3 – 41.6 bats/turbine/year (Arnett et al, 2007; Kunz et al, 2007; Marsh, 2007; Nicholls and Racey, 2007; Arnett et al, 2008; Horn et al, 2008b). Migration and Behavioral Patterns. The majority of injuries and fatalities (approximately 90%) appear to occur within a few hours after sunset, and during the midsummer and the early fall, coinciding with southward migration patterns (Arnett et al, 2007; Cryan and Brown, 2007; Kunz et al, 2007; Kuvlevsky et al, 2007; Marsh, 2007; Nicholls and Racey, 2007; National Research Council, 2007; Arnett et al, 2008; Cryan, 2008; Horn et al, 2008a,b). Cryan (2008) suggests that these collisions may be a result of mating behaviors where the central feature is the tallest tree in the area. These tall trees become the rendezvous points for mating bats that have been sexually segregated until the fall migration. Since bat fatalities are often skewed toward adult males, this gives credence to the idea that the intersection of roosting habitat potentially provided by wind turbines and autumn mating behavior may be a contributing cause of fatalities at wind turbines (Cryan and Brown, 2007; Cryan, 2008). However, recent studies have posed many hypotheses and some empirical evidence to explain spatial and temporal patterns of bat collisions with wind turbines. Bats are often struck when foraging and feeding around the turbines, and not apparently when they are attempting to pass straight through the turbines (Kunz et al, 2007; Horn et al, 2008a) or looking for a place to roost. Light sources attached to turbines, as well as the heat produced by them, may cause an increase in insects attracted to the lights, which then attracts bats (Horn et al, 2008a,b). During foraging, the presence of insect prey around a turbine may contribute to a collision and echolocation is only effective at a distance of 10 meters or less (Kunz et al, 2007), which may not provide sufficient time for a bat to detect a turbine and avoid a collision. There may also be an increase in the insect population caused by the edge created between the forest and the man-made environments, causing more bats to gather due to the increased abundance in prey (Kunz et al, 2007; National Research Council, 2007; Horn et al, 2008a). Infrastructure. It has been suggested that bats navigate by vision when migrating and are therefore drawn to highly-visible tall structures that may provide roosting spots, such as turbines, and are then struck by the blades as they investigate the masts (Cryan and Brown, 2007; Barclay et al, 2007; Kunz et al, 2007; Arnett et al, 2008; Horn et al, 2008a,b). Bats tend to fly between 100 – 500 meters above the ground and night-flying passerines fly at similar or higher altitudes, suggesting that taller turbines may be the cause of more deaths and injuries than smaller turbines (Barclay et al, 2007; Arnett et al, 2008). This theory was verified in a study conducted by Barclay et al (2007) where the authors found that as tower height increased, especially over 65 meters, so too did bat fatalities, regardless of the size of the rotors. Bats could possibly be attracted to the movement or the sound of the moving blades (Barclay et al, 2007). Electromagnetic fields given off by the turbines may interfere with some bats’ abilities to perceive the closeness of objects, thus leading to collisions with turbine blades (Kunz et al, 2007). Bat collisions appear to occur when the blades are spinning and not when they are stationary (Arnett et al, 2008) due to the “motion smear” effect, indicating that bats may not perceive the spinning blades or have enough reaction time to avoid them (Barclay et al, 2007; Horn et al, 2008a). Vortices caused by the rotating blade tips may cause foraging bats that are too close to the turbine to become caught and have difficulty escaping (National Research Council, 2007). It has been postulated that barotrauma, a rapid reduction of air pressure in the lungs near revolving turbine blades, is a leading cause of bat mortality. This may be partially due to bats having more pliable lungs than birds, thus making them more susceptible to sudden drops in pressure (Kunz et al, 2007; Baerwald, 2008). Weather Patterns. Strikes and fatalities tend to occur most frequently right before and after storms have passed through (Arnett et al, 2007; Kunz et al, 2007; Horn et al, 2008a,b). It has been suggested that low cloud ceilings or intense fog may cause migrating bats, as well as migrating birds, to fly at a lower altitude, in addition to hampering their ability to see or sense tall structures (Cryan and Brown, 2007; Kunz et al, 2007). Bats appear to be more active at times of low barometric pressure and low wind speed, which when combined with wind direction, directly contributes to strike occurrences (Cryan and Brown, 2007; Arnett et al, 2008; Horn et al, 2008b) due to the more abundant insect prey population, as was demonstrated in a study by Redell et al (2006) at a proposed wind farm located near a large hibernaculum in Wisconsin. Threats and Risks to Sea Life Marine mammals and benthic habitats are also impacted by the development and operation of offshore wind facilities. Figure 5 illustrates how noise, the primary impact, and infrastructure may affect sea life and habitats. Habitat Loss and Displacement. A temporary loss of habitat may be expected due to construction activities. Sediment suspension and deposition will most likely result from the jet blowing activities that will occur in order to place the turbines into the sea bed (MMS, 2009). Benthic organisms, such as crabs (Brachyura) and lobsters (Nephropidae) may be displaced due to construction and operation of the turbine structures and associated cables, which may ultimately affect sea animals (e.g., leatherback turtles [Dermochelys coriacea] and Kemp’s ridley turtles [Lepiochelys kempii]) that prey on them (Söker et al, 2000; MMS, 2009). However, sedentary organisms, such as the northern quahog (Mercenaria mercenaria) and the eastern oyster (Crassostrea virginica), will most likely be subject to mortality due to their inability to avoid the sediment deposition. Once construction is finished, the majority of the species originally displaced will most likely return (MMS, 2009). Collisions. Collisions and strikes of sea animals with vessels performing maintenance on turbines is a possibility as well. The waters off the east coast of the United States contain a large number of cetaceans, thereby making injuries and possibly death due to collisions with vessels more likely. The most common whales susceptible to strike along the eastern shore include finback (or fin) whales (Balaenoptera physalus), humpback whales (Megaptera novaeangliae), North Atlantic right whales (Eubalaena glacialis) gray whales (Eschrichtius robustus), minke whales (Balaenoptera acutorostrata), southern right whales (Eubalaena australis) and sperm whales (Physeter macrocephalus). Seals (Phocidae) will also be at an increased risk of injury or mortality due to collision during construction of the facilities (MMS, 2009). 
Figure 5. Possible environmental impacts of offshore wind energy during exploration, construction, and operation (Elliott, 2002). Noise. Noise produced by the construction of turbines is especially detrimental to sea life and may cause temporary hearing loss or permanent injury, particularly in seals, porpoises (Phocoenidae) and fin whales (National Marine Fisheries Service, 2006; Snyder and Kaiser, 2009a; MMS, 2009). Pile driving a turbine monopile into the seabed can cause sound pressure to be felt up to 400 meters away from the source. The activity would be heard by porpoises and seals up to 80 km away from the activity, as well as causing hearing loss in porpoises up to 1.8 km away (Snyder and Kaiser, 2009a). Behavioral changes may occur up to 20 km away (Snyder and Kaiser, 2009a) and injuries may occur up to 100 meters away from the source (Nedwell et al, 2007). In most cases, noise from general operation, once construction has ended, is consistent with the normal background noise experienced by sea animals before construction began (Nedwell et al, 2007; Snyder and Kaiser, 2009a; MMS, 2009). However, the normal operation of the turbines may still be heard up to 1 km away (Snyder and Kaiser, 2009a). While normal operational noise will most likely have little to no affect on sea animals (MMS, 2009), there is the possibility that some mammals will avoid the sites around the turbines, especially sites that may have previously been used as breeding and haul-out sites (Snyder and Kaiser, 2009a), or as migratory pathways (Nedwell et al, 2007). Fish and cetaceans (e.g., baleen whales [Mysticeti]) are also very sensitive to sound, and the construction and operation of offshore turbines may cause avoidance and displacement to occur at distances up to 320 meters from the source (Söker et al, 2000; Snyder and Kaiser, 2009a). Threats and Risks to Other Wildlife According to the National Research Council (2007), the disturbance and/or destruction of red spruce (Picea rubens) forests caused by turbine installation may have an adverse impact on populations of the Virginia northern flying squirrel (Glaucomys sabrinus fuscus), which prefer to make this particular habitat their home. Allegheny woodrats (Neotoma magister) may also be negatively affected by the installation of wind turbines. These mammals prefer to nest at least 2 km from man-made structures and roads; therefore, installation of turbines near their nests will most likely cause them to avoid prior nesting habitats. Other animals that could be locally displaced include the snowshoe hare (Lepus americanus), black bear (Ursus americanus), beaver (Castor canadensis), raccoon (Procyon lotor), white-tailed deer (Odocoileus virginianus), red and gray foxes (Vulpes vulpes and Urocyon cinereoargenteus), mink (Mustela vison), and many others (National Research Council, 2007). EXAMINATION OF SOLUTIONSIntroductionThere are mitigation efforts and strategies available in order to encourage the development of this clean energy source while reducing environmental and wildlife impacts. The most important generally-applicable mitigation effort would be to avoid environmentally-sensitive areas, such as critical or fragile habitats, as well as those areas that are considered to be migration routes and flight paths. Many of the ideas described below are most useful in a species- and/or location-specific context. Mitigation Efforts and StrategiesHabitats. The most important mitigation strategy is to avoid ecologically sensitive areas (Berry et al, 2005), as well as those locations where there is a high density of migratory waterfowl or waders, high levels of raptor activity (e.g., breeding ranges and pass-through flight paths), and breeding or migrating populations of less abundant species (Drewitt and Langston, 2006; Drewitt and Langston, 2008). Road construction on steep slopes should also be avoided (Berry et al, 2005). Travel to and within the wind development area should be restricted during certain times of the year (e.g., migration seasons of land mammals) to minimize disturbance (Morrison and Sinclair, 2004). New turbines placed next to areas that have already been developed may aid in minimizing disturbances to habitats (Drewitt and Langston, 2008). Turbine pad areas that were initially cleared should be allowed to return to their natural state once the turbines have been built (Morrison and Sinclair, 2004; Berry et al, 2005). Bird Species. At all proposed locations, areas near breeding and nesting sites should be excluded due to possible avoidance and displacement of birds, especially with seabirds that avoid areas with wind farms (Snyder and Kaiser, 2009a). Certain locations where birds may stop on migration (e.g., Cape May, New Jersey and Delaware Bay) should also be avoided due to their migratory importance (Snyder and Kaiser, 2009a). The interaction of topography and weather for onshore facilities should be assessed to determine if conditions are too dangerous for foraging raptors and passerines (Hoover, 2005). Deflection updrafts (topographical inclination and elevation combined with wind speed and direction) are used for soaring purposes while foraging for food. Powering down the turbines during the strongest winds that are perpendicular to the turbines will help to reduce the number of injuries or deaths (Hoover, 2005; Drewitt and Langston, 2008). Likewise, placing turbines on the leeward side of ridges may minimize raptor collision rates according to a study conducted by Smallwood and Neher (2004), who found that raptors, particularly red-tailed hawks, American kestrels, and golden eagles, prefer to fly on the windward side of ridgelines. The physical placement of turbines is just as important as the location. Turbine rows should be placed parallel to the flight path instead of across it (Drewitt and Langston, 2008). The turbines should be set back from the edges of cliffs so that soaring birds will be less likely to collide with them (California Energy Commission, 2007; Drewitt and Langston, 2008). With the use of taller towers, turbines can be spaced farther apart, which helps minimize the risk of collision as it allows more room to maneuver between the towers (Morrison and Sinclair, 2004; Marsh, 2007). However, Drewitt and Langston (2008) contend that turbines clustered together, as opposed to being spaced farther apart, may encourage migrating or foraging birds to circumvent the turbines instead of trying to fly through the space between them. An attempt at making the turbines and rotor blades more visible may help decrease the risk of collisions. Blades should be painted in a way that draws attention to them and makes them more noticeable, such as a single black blade paired with two white blades (Morrison and Sinclair, 2004; Hoover, 2005). However, using UV-light reflective paint apparently had no significant effect according to a study conducted by Young et al (2003). Adding a square or rectangular attachment at the end of a blade may make the blades more noticeable to birds and easier for them to avoid (Morrison and Sinclair, 2004). Adding a whistling effect to turbine blades, in the range of 2-4 kHz, may help birds avoid colliding with turbines while having no noticeable effect to the overall noise generated by the turbine; this device, however, may eventually become obsolete as the birds might become habituated to the sound over time and begin to ignore it (Dooling, 2002; Morrison and Sinclair, 2004). If lights are placed on turbines due to Federal Aviation Administration (FAA) requirements, they should provide the least amount of luminosity and a minimum of intermittent flashing, as opposed to solid or regularly flashing red or white lights; floodlights should be pointed down towards the ground (Drewitt and Langston, 2006; Kerlinger, 2006; California Energy Commission, 2007; Newton, 2007; Drewitt and Langston, 2008). Turbines should be anchored with materials that do not allow for burrowing animals that attract raptors (California Energy Commission, 2007; Drewitt and Langston, 2008), and vegetation near the turbines should be allowed to grow tall so that small prey animals are less visible to raptors (Thelander and Smallwood, 2004; Kerlinger, 2006). Strategies should be selected and tailored to site conditions. Bat species. Unfortunately, little is known about bats and their migration, as well as their foraging and roosting habits. However, mitigation options are still available to help minimize the risk of injury or death due to wind turbines. As with birds, bat activity levels should be assessed prior to construction in order to aid in determining placement of turbines in areas that will pose the least risk (Arnett et al, 2007), such as away from open water sources or near known cave roosts (Arnett et al, 2008). Since bats use echolocation to track insect prey, the use of acoustic deterrents which interrupt normal echolocation at irregular intervals may dissuade bats from flying through or around turbines (Spanjer, 2006; Horn et al, 2008b). Exposure to electromagnetic fields greater than 2 v/m (volts/meter) has been suggested as a possible deterrent (Nicholls and Racey, 2007) based on bat abundance data in the vicinity of military radar towers. Bat fatality could also be reduced if turbine operations are shortened on nights with low wind speeds, particularly during the migration season when more bats are present in the area (Marsh, 2007; Arnett et al, 2008; Horn et al, 2008a,b). In a recent studies (Arnett et al, 2009; Baerwald et al, 2009), curtailing operations in this way showed a reduction rate of 53% - 87% in bat fatalities, while only reducing annual power output minimally. Sea Life. Critical habitat for species managed by NOAA and FWS (e.g., North Atlantic Right Whale [Eubalaena glacialis] and Stellar Sea Lion [Eumetopias jubatus]) should be avoided (Snyder and Kaiser, 2009a). Before pile driving, a buffer zone of 750 meters around each potential monopile should be established to minimize injury to sea animals (Minerals Management Service, 2009). During construction, pile driving should start with soft strikes and gradually build up to full strength in order to minimize noise levels and give sea mammals time to leave the area (Nedwell et al, 2007; MMS, 2009). Alternatives to pile driving are available, however. Gravity foundations may be used for turbines instead of pile driving monopiles into the seabed. This type of foundation is made from concrete, rests on the sea bed, and uses its own gravity to stabilize the structures; these foundations will cause fewer disturbances to marine life during construction and may even function as new habitats for benthic organisms. Another alternative would be to use suction foundations to attach the turbine to the sea bed; suction is applied to steel baskets resting on the sea floor, causing the foundations to sink more firmly into the sea bed with a minimum of noise (Snyder and Kaiser, 2009a). Once the turbines have been constructed, anti-perching devices should be affixed to turbine structures to deter seabirds and waterbirds from perching on the railings and deck areas and possibly harming themselves (MMS, 2009). Best Management Practices In general, the ideal suite of studies and measures will be determined through a site-specific and species-specific scoping exercise and in consultation with all site stakeholders. Along with mitigation efforts, there are numerous practices that can be applied before installation, during operation, and during decommissioning. Some of these practices include: Sensitive areas should be avoided (Drewitt and Langston, 2006). Biological surveys should be conducted at each proposed site in order to determine if there will be any adverse effects to siting a turbine in that area (Berry et al, 2005). Migration studies of birds and bats at individual sites should be conducted. Surveys could include marine radar, thermal imaging cameras, bat echolocation detectors, ceilometers, and NEXRAD radar surveys (Berry et al, 2005). Pre-construction surveys should also be conducted to determine effects on migratory neotropical birds and other birds of special concern that may be protected under the Migratory Bird Treaty Act (16 United States Code 703-712) (Johnson et al, 2002). Full-season pre- and post-construction studies should be conducted on the type and abundance of species present in the region, as well as their activities, over several years using an array of techniques and instruments to determine migration, roosting and foraging patterns, and interactions with the turbines (Kunz et al, 2007). Studies should be tailored to risk. Surveys lasting a minimum of one year should be conducted prior to construction. The surveys should include habitat surveys, migration and breeding surveys of raptors and passerines, and bat acoustic studies. If an expanded study is recommended, radar studies for migrating birds and bats, waterfowl surveys, wintering bird surveys, and expanded studies of migrating bats may be necessary as well (NYDEC, 2009). It has been recommended that studies on nocturnal migrants should begin ½ hour after sunset and continue through ½ hour after sunrise during a minimum of one full fall and spring season for at least 20-30 nights in order to experience responses to different weather patterns (Maine Audubon, 2006). It has been recommended that surveys of raptors should be conducted for a minimum of six days during the spring and a minimum of 10 days during the fall, during normal business hours (i.e., 9:00 am – 5:00 pm), and should coincide with peak migration times. Studies of diurnal passerines should be conducted for a minimum of 10-15 days during both the spring and fall seasons; the best times to perform these surveys occur between dawn and 10:00 am (Maine Audubon, 2006; Pennsylvania Game Commission, 2007b; NYDEC, 2009). Acoustic monitoring of bats should be conducted for one full year during the spring and fall migration periods during pre-construction, as well as another full year post-construction, beginning ½ hour after sunset and continuing until ½ hour before sunrise (Maine Audubon, 2006; Pennsylvania Game Commission, 2007a; NYDEC, 2009). Post-construction mortality surveys for birds and bats should be conducted for 2-3 years after the facilities become operational (Maine Audubon, 2006; MMS, 2009). Post-construction surveys should occur for two years and include mortality surveys (i.e., ground searches for bird and bat carcasses), bird and bat avoidance surveys, and acoustical monitoring for bats (Pennsylvania Game Commission, 2007a; NYDEC, 2009), as well as acoustical monitoring for seabirds (MMS, 2009). Post-construction monitoring to document habitat disturbance and recovery for seafloor habitats and benthic communities should be instituted (MMS, 2009). Use of spatial design and collision models may help to determine the location least likely to cause bird and bat collisions (Madders and Whitfield, 2006). Siting of projects should occur in areas where the habitat is poor (e.g., agricultural and more developed areas) in order to minimize fragmentation and disturbance when possible (Winegrad, 2004). Meteorological towers should be constructed in such a way that perching and nest-building are discouraged (Winegrad, 2004). The design of the wind turbine should take into account the size and height of the turbine, as well as the diameter of the rotor-swept area (Kunz et al, 2007). Bat activities at currently existing sites should be studied with respect to different weather patterns, wind speeds, and turbine operations (Kunz et al, 2007). Pre-existing roads, transmission facilities, and cable routes should be used as much as possible to minimize damage to habitats (American Bird Conservancy, 2004). Power lines should be buried under ground as much as possible (Kerlinger, 2006; California Energy Commission, 2007). During migration and times with low visibility (e.g., inclement weather), shutting down operations to minimize collision risks should be considered (Morrison and Sinclair, 2004). Curtailment at low wind speeds is highly recommended. An Environmental Management System (EMS) should be instituted to constantly strive for improvement in managing and minimizing potential environmental impacts (MMS, 2009). A professional observer should be placed at offshore facilities to alert and halt construction activities if a sea animal comes within the established buffer zone (MMS, 2009). When embedding underwater cables, which should be at a minimum depth of six feet, the developer should use a low-impact hydraulic jet blow in order to minimize sediment disturbance (MMS, 2009). Maintenance trips to offshore facilities should be carefully timed to reduce disturbance caused by boats and personnel (Drewitt and Langston, 2006). Once turbines are no longer in use, they should be removed immediately, or laid down on the ground to minimize impacts, and the land allowed to return to its natural state (Thelander and Smallwood, 2004; Marsh, 2007; Drewitt and Langston, 2008). ACKNOWLEGEMENTS This report was produced with the financial support of the following: the Wildlife Action Opportunities Fund, which is administered by the Wildlife Conservation Society on behalf of the Doris Duke Charitable Foundation, the Island Foundation, and Manomet Center for Conservation Sciences. We are grateful to Dave Cowan, First Wind, and an anonymous reviewer who provided insightful comments on an earlier version of this report. CITATIONS Abbasi, S.A. and Abbasi, N. 2000. The likely adverse environmental impacts of renewable energy sources. Applied Energy, 65: 121-144. 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