DEPAR TMENT OF AGRICULT URE

United States 

Department of 

Agriculture

Forest Service

Pacific Northwest 

Research Station

General Technical 

Report

PNW-GTR-863

July 2012

Synthesis of Wind Energy 

Development and Potential 

Impacts on Wildlife in the 

Pacific Northwest, Oregon 

and Washington

Miranda H. Mockrin and Rebecca A. Gravenmier
The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood, 

water, forage, wildlife, and recreation. Through forestry research, cooperation with the 

States and private forest owners, and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide increasingly greater service to a 

growing Nation.

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large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice 

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1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (800) 795-3272 (voice) 

or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.

Authors

Miranda H. Mockrin is a research biologist, Rocky Mountain Research 

Station, 2150 Centre Avenue, Building A, Fort Collins, CO 80526; and Rebecca A.

Gravenmier is a natural resource specialist, Pacific Northwest Research Station, 

333 SW First Avenue, Portland, OR 97205.

Cover photographs: top left, Dennis E. Schwartz; top right, Paul Cryan, USGS; 

bottom, Michael Schroeder, WA DFW. 
Abstract 

Mockrin, Miranda H.; Gravenmier, Rebecca A. 2012. Synthesis of wind 

energy development and potential impacts on wildlife in the Pacific Northwest, 

Oregon and Washington. Gen. Tech. Rep. PNW-GTR-863. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station. 

55 p.

Nationally, there is growing public interest in and policy pressure for developing 

alternative and renewable sources of energy. Wind energy facilities in the Pacific 

Northwest expanded rapidly over the past decade, as a result of state policies that 

encourage wind energy development. While much of the development thus far 

has occurred on private lands, there is interest in expanding onto federal land. 

However, there are concerns about the impacts of wind energy on wildlife. Wind 

energy facilities have the potential to harm wildlife both directly through collisions with turbines and transmission lines, and indirectly by modifying habitat. 

This report synthesizes the available scientific literature on potential wind energy 

facility impacts to wildlife, with a focus on the Pacific Northwest (Oregon and 

Washington), and summarizes the current best management practices recommended in federal and state guidelines for wind energy development. Research gaps 

in our understanding of wind energy impacts on wildlife remain. Future research 

needs include long-term, multisite, experimental studies of wind energy impacts 

on wildlife, improved ability to estimate population-level and cumulative impacts 

of wind energy facilities on wildlife, and better knowledge of key wildlife species’ 

migration and demography.

Keywords: Wind energy, turbine, wildlife, Pacific Northwest, Oregon, 

Washington.
Contents

1 Introduction

1 Background on Wind Energy Development

9 Description of a Wind Energy Facility

12 Science Findings: The Effects of Wind Energy Facilities on Wildlife

12 Habitat Loss and Modification

17 Direct Mortality and Behavior

26 Best Management Practices to Minimize Effects of Wind Energy Facilities 

on Wildlife

29 Site Selection

33 Preconstruction Wildlife Surveys

36 Construction and Operation Practices

37 Postconstruction Monitoring

40 Future Research Needs for Minimizing Effects of Wind Energy Facilities 

on Wildlife

40 General Research Needs

41 Research Needs for Minimizing Habitat Loss or Modification

43 Research Needs for Minimizing Direct Mortality

44 Conclusion

45 Acknowledgments

45 English Equivalents

46 Literature Cited
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Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Introduction

Wind energy development has increased substantially on private land in the Pacific 

Northwest, and there is growing interest in development on public lands. This 

report brings together information on wind energy development in the region, 

potential impacts on wildlife, and best management practices and guidelines for 

development, to provide federal and state land managers, biologists, and policymakers in the Pacific Northwest with information that can advise policies, land use 

decisions, or environmental impact analyses. Specifically, we present background 

information on the structure and operation of wind energy facilities, including associated facilities such as roads and transmission lines. We then summarize current 

peer-reviewed science pertaining to the effects of wind energy facilities on terrestrial fauna, and provide an overview of current best management practices and 

recommendations for wind energy development, drawn from federal and state wind 

energy development guidelines. Best management practices are cross-referenced to 

peer-reviewed science (where applicable or available). We conclude with a summary 

of the current research needs for management.

Background on Wind Energy Development

Nationally, there is growing public interest in and policy pressure for developing 

alternative and renewable sources of energy. In 2010, wind development in the 

United States increased by over 5,000 megawatts (MW) of new generating capacity, a national rise in capacity of 15 percent to a total of just over 40,000 MW 

(American Wind Energy Association 2011). This increase fell below growth seen in 

2008 and 2009 (increases of more than 8,500 MW and 10,000 MW, respectively), 

owing in part to changes in federal incentives (American Wind Energy Association 

2011). Globally, the United States is one of the fastest growing producers of wind 

energy, although wind power represents approximately only 2 percent of total U.S. 

electricity generation (U.S. Department of Energy 2010). Development is expected 

to continue, and even accelerate, as the U.S.’ energy policy emphasizes independence from imported petroleum and reduction of carbon emissions. Wind-generated 

electrical energy is renewable and has a number of environmental benefits: electricity is produced without air pollution, greenhouse gas emissions, water consumption, 

mining, waste storage, and other problems associated with many traditional forms 

of energy generation. 

To be effective, wind energy developments must be located in open areas with 

high windspeeds, with connections to transmission lines. Wind resources are often 

greatest in uplands, grasslands, and as well as offshore, coastal areas. Nationally, 

wind resources are greatest in the Midwestern United States from Texas to North 
2

general technical report pnw-gtr-863

Dakota (U.S. Department of Energy 2008). However, current wind energy facilities 

are concentrated both in the Midwest and the Western United States, including California, Oregon, and Washington. The decision to site a wind energy facility occurs 

not just in response to wind resources, but also to electricity pricing, state and local 

policies, and access to transmission lines (U.S. Department of Energy 2011). In 

2010, only seven states had more than 2,000 MW of wind power capacity, including Washington and Oregon (both had just over 2,100 MW online in 2010, ranking 

them fifth and sixth nationally) (American Wind Energy Association 2011). Wind 

energy facilities in the Pacific Northwest have grown quickly, partially as a result 

of favorable state policies that encourage wind energy development, and renewable 

energy is expected to continue to grow in the region. Oregon law requires utilities 

to provide 25 percent renewable energy to their customers by 2025, and the state 

has established goals to reduce greenhouse gas emissions by 75 percent below 1990 

levels by 2050 (Oregon Columbia Plateau Ecoregion Wind Energy Taskforce 2008). 

In 2006, Washington passed legislation requiring 15 percent of the electricity sold 

in the state by 2020 be derived from renewable sources, with a reduction in greenhouse gas emissions to 50 percent below 1990 levels by 2050 (Washington Department of Fish and Wildlife 2009).

Nationally, development of wind energy facilities has been mostly concentrated on private land. However, there is increasing interest in developing 

wind energy facilities on federal lands. Under Executive Order 13514, federal 

agencies are instructed to implement renewable energy projects on federal 

lands (Executive Order 13514 74 FR 52117, October 8, 2009). Nationally, the 

U.S. Department of the Interior, Bureau of Land Management (BLM) had 

327 MW of installed wind capacity under 25 right-of-way authorizations by 

January 2009, with another 167 right-of-way authorizations approved (USDI 

Bureau of Land Mangement 2009). Guidance for BLM’s wind energy program 

was developed through a Westwide planning process that established policies 

and best management practices for all BLM lands, amending 52 land use 

plans (USDI Bureau of Land Management 2005). The U.S. Department of 

Agriculture, Forest Service released final directives for wind energy projects 

in August 2011 (76 CFR 47354 2011). These internal directives provide standardized direction and guidance for wind energy projects on National Forest 

System lands (USDA Forest Service 2011a, 2011b). The Forest Service chose 

not to pursue a national environmental impact assessment and planning 

process, concluding it would be more efficient to examine individual sites 

as projects are proposed (76 CFR 47354 2011). The Forest Service currently 

has no approved wind energy projects, but as of June 2011, had one accepted 
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Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

application for a wind energy project in Vermont, a number of proposals 

indicating interest in southern California, and 15 meteorological tower/wind 

energy testing sites nationwide.1

In the Pacific Northwest, the majority of wind energy development thus far has 

also taken place on private lands, much of it concentrated (fig. 1). However, interest 

in public lands in the region is growing: applications for wind-testing meteorological towers on BLM lands in Oregon and Washington increased from 6 permits per 

year in 2006 to 24 in 2008 (Morris 2009). By March 2011, BLM lands had one wind 

energy facility application (0.42 km2) and 19 meteorological towers, as well as five 

pending wind energy facility applications (122 km2), and 16 proposed meteorological towers.2

 The Forest Service has also received proposals for meteorological 

towers on the Fremont-Winema and Olympic National Forests.3 One full-scale 

wind energy facility prospectus has been received by the Forest Service for a 400-

MW project in the Fremont-Winema National Forest (up to 175 wind turbines over 

260 km2) (see footnote 3).

Wind energy is likely to continue to grow nationally and regionally on all 

types of land ownership, which raises concerns about the impacts of wind energy 

developments on wildlife (Arnett et al. 2008, Kunz et al. 2007b, National Research 

Council 2007). Wind energy facilities have the potential to harm wildlife both 

directly through collisions with wind turbines and infrastructure, and indirectly 

by modifying habitat. Land managers of Pacific Northwest forests and rangelands 

require information on the effects of wind energy facilities on wildlife and information on the current best management practices, as supported by scientific studies. 

This report is a synthesis of these potential impacts to wildlife, with a focus on the 

Pacific Northwest (Oregon and Washington states). After presenting background 

information on the operation of a wind energy facility and a summary of current 

peer-reviewed science on the effects of wind energy facilaties on the terresterial 

fauna we present an overview of the guidelines and best practices from the U.S. 

Fish and Wildlife Service (USFWS), BLM, and Forest Service, and the states of 

Oregon and Washington, cross-referenced to peer-reviewed science (table 1).

1

 Parker, G. 2011. Personal communication. Realty specialist, Energy Uses, Lands and 

Realty Management Staff, USDA Forest Service, 1400 Independence Ave., SW, Mailstop 

1124, Washington, DC 20250. 

2

 Jensen, C. 2011. Personal communication. Lands section chief, Bureau of Land Management, Oregon State Office, 333 SW 1st Avenue, Portland, OR 97204. 

3

 Sauser, J. 2011. Personal communication. Regional land use program manager, Lands 

and Recreation Residence Special Uses, USDA Forest Service, Pacific Northwest Regional 

Office, 333 SW 1st Avenue, Portland, OR 97204. 

Wind energy is 

likely to continue to 

grow nationally and 

regionally on all types 

of land ownership, 

which raises concerns 

about the impacts 

of wind energy 

developments on 

wildlife.
4

general technical report pnw-gtr-863

Figure 1—Wind energy projects and status on private land in Oregon and Washington. Data courtesy of Renewable 

Northwest Project (2011).

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5

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Table 1—Best management practices (BMPs), from U.S. Department of the Interior, U.S. Fish and Wildlife 

Service (USFWS) (2011d), U.S. Department of Agriculture, Forest Service (FS) (2011a,b), U.S. Department of the 

Interior, Bureau of Land Management (BLM) (2005a,b), Oregon (OR) (Oregon Columbia Plateau Ecoregion Wind 

Energy Taskforce 2008), and Washington (WA) (Washington Department of Fish and Wildlife 2009)a

 Resource

BMPs to reduce habitat loss and avoidance Source concern Citation/reference

Establish nondisturbance buffer zones to protect USFWS Sensitive Buffer zones would differ 

sensitive habitats or areas of high risk for species habitats, with species. References for 

of concern identified in preconstruction studies. species of sage grouse literature

Determine the extent of the buffer zone in consultation concern include Connelly et al. 

with the USFWS and state, local, and tribal wildlife 2000, Naugle et al. 2011 

biologists, and land management agencies (e.g., BLM and Walker et al. 2007. 

and FS) or other credible experts as appropriate.

Restore wildlife habitat temporarily disturbed during USFWS, Wildlife Standard operating 

the construction, maintenance, or repair of the project. FS, BLM, habitat procedure.

Minimize habitat disturbance before and during and OR

construction. From USFWS: “Use available data from 

state and federal agencies, and other sources (which 

could include maps or databases), that show the 

location of sensitive resources and the results of Tier 2 

and/or Tier 3 studies to establish the layout of roads, power 

lines, fences, and other infrastructure.”

Mitigate temporary and permanent impacts to wildlife USFWS, Wildlife Standard operating 

habitat and populations. See appropriate guidelines for FS, BLM, habitat procedure.

more specific information on mitigation. Private OR, and WA

developers and federal managers will have to work 

with the USFWS to comply with relevant legislation 

for some species (Endangered Species Act, Bald and 

Golden Eagle Protection Act, Migratory Bird Treaty Act). 

Avoid or minimize construction during periods when FS, Wildlife, Standard operating 

it will disturb wildlife (e.g., avian nesting season or BLM, generally procedure.

winter for overwintering game). and OR

Reduce fire hazards. Exact guidance differs among USFWS, Wildlife Standard operating

guidelines. For USFWS, “Reduce fire hazard from FS, OR, habitat procedure.

vehicles and human activities...Site development and and WA 

operation plans should specifically address the risk of

wildfire and provide appropriate cautions and measures

to be taken in the event of a wildfire.”
6

general technical report pnw-gtr-863

Table 1—Best management practices (BMPs), from U.S. Department of the Interior, U.S. Fish and Wildlife 

Service (USFWS) (2011d), U.S. Department of Agriculture, Forest Service (FS) (2011a,b), U.S. Department of the 

Interior, Bureau of Land Management (BLM) (2005a,b), Oregon (OR) (Oregon Columbia Plateau Ecoregion Wind 

Energy Taskforce 2008), and Washington (WA) (Washington Department of Fish and Wildlife 2009)a

 (continued)

 Resource

BMPs to reduce habitat loss and avoidance Source concern Citation/reference

Instruct personnel to avoid harassment or disturbance USFWS, Wildlife Standard operating 

of wildlife. FS, BLM, procedure.

OR, and WA

Reduce the introduction and spread of invasive plants, USFWS, Wildlife Standard operating 

using applicable local policies (e.g., use native species FS, BLM habitat procedure.

when seeding or planting during restoration, cleaning OR, WA 

vehicles and equipment arriving from areas with 

known invasive species issues, using locally sourced 

topsoil, and monitoring for and rapidly removing 

noxious weeds at least annually). Utilize pest and weed 

control measures as specified by county or state

requirements, or by applicable federal agency 

requirements (such as Integrated Pest Management) 

when federal policies apply.

Minimize, to the extent practicable, building new roads USFWS, Wildlife Standard operating 

and infrastructure. Use existing roads and infrastructure FS, BLM, procedure.

when feasible. and OR

Use explosives at specified distances to sensitive BLM Wildlife, Standard operating

wildlife or streams and lakes, as established by aquatic procedure.

appropriate agency. resources

Minimize stream crossings (OR) and avoid impact USFWS, Aquatic Standard operating 

to hydrology and stream morphology, especially FS, OR, resources procedure.

where federal- or state-listed aquatic or riparian species and WA 

may be involved (USFWS). All guidelines mention the 

Clean Water Act and water quality. More specific text

within OR and USFWS. From USFWS, “Minimize 

impacts to wetlands and water resources by following 

all applicable provisions of the Clean Water Act (33 

USC 1251-1387) and the Rivers and Harbors Act (33 

USC 301 et 16 seq.); for instance, by developing and 

implementing a storm water management plan and 

taking measures to reduce erosion and avoid delivery 

of road-generated sediment into streams and waters.”

Follow federal and state measures for handling toxic USFWS Wildlife, Standard operating 

substances to minimize danger to water and wildlife aquatic procedure.

resources from spills. resources

Manage vehicles and traffic volumes to reduce wildlife USFWS, Wildlife Standard operating

disturbance. BLM, OR, procedure.

and WA
7

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Table 1—Best management practices (BMPs), from U.S. Department of the Interior, U.S. Fish and Wildlife 

Service (USFWS) (2011d), U.S. Department of Agriculture, Forest Service (FS) (2011a,b), U.S. Department of the 

Interior, Bureau of Land Management (BLM) (2005a,b), Oregon (OR) (Oregon Columbia Plateau Ecoregion Wind 

Energy Taskforce 2008), and Washington (WA) (Washington Department of Fish and Wildlife 2009)a

 (continued)

 Resource

BMPs to reduce direct mortality Source concern Citation/reference

Minimize construction and management practices that USFWS, Wildlife, Standard operating 

may attract wildlife, both prey and predators, to the BLM, raptors procedure. Raptor 

wind energy facility. Manage garbage, animal and WA information from Smallwood 

carcasses, and structure construction and management et al. 2009, Smallwood and 

practices to avoid increasing wildlife density and Thelander 2008. 

raptor activity at the wind energy facility (e.g., avoid 

increasing prey populations through vegetation 

manipulation, as that may increase raptors) (BLM), 

avoid habitat enhancements such as nesting platform 

or nest boxes, ponds, guzzlers, etc. (USFWS). 

Locate turbines to avoid separating bird and bat species USFWS Birds and Standard operating 

of concern from their daily roosting, feeding, or and BLM bats procedure. Research thus 

nesting sites, if documented that the turbines’ presence far shows that turbines 

poses a risk to species (USFWS). primarily strike migratory 

bats (not local roosting 

colonies) (Arnett et al. 

 2008).

All guidelines state that bird perching should be USFWS, Birds, Problems with bird perching 

discouraged. From OR, “Anti-perching devices FS, BLM, specifically, reviewed in Avian Power

should be installed on transmission pole tops OR, and WA raptors Line Interaction Committee 

and cross arms where the poles are located (2006).

within 0.5 mile of turbines.”

Avoid use of guy wires on permanent meteorological USFWS, Birds Longcore et al. 2008. 

towers. From USFWS guidelines: “If guy wires are FS, BLM,

necessary, bird flight diverters or high visibility OR, and WA

marking devices should be used.” 

All guidelines discuss BMPs for reducing avian USFWS, Birds Avian Power Line 

collisions from power lines. From USFWS, “Place low FS, BLM, Interaction Committee 

and medium voltage connecting power lines associated OR, and WA 2006, Longcore et al. 2008. 

with the wind energy development underground to the 

extent possible, unless burial of the lines is prohibitively 

expensive (e.g., where shallow bedrock exists) or where 

greater adverse impacts to biological resources would 

result.” USFWS guidelines provide more information on 

when overhead lines may be acceptable and recommend 

that to the extent possible Avian Power Line Interaction Committee 

2006 guidelines be followed for overhead lines, aboveground 

low and medium voltage lines, transformers, and conductors. 
8

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Table 1—Best management practices (BMPs), from U.S. Department of the Interior, U.S. Fish and Wildlife 

Service (USFWS) (2011d), U.S. Department of Agriculture, Forest Service (FS) (2011a,b), U.S. Department of the 

Interior, Bureau of Land Management (BLM) (2005a,b), Oregon (OR) (Oregon Columbia Plateau Ecoregion Wind 

Energy Taskforce 2008), and Washington (WA) (Washington Department of Fish and Wildlife 2009)a

 (continued)

 Resource

BMPs to reduce direct mortality Source concern Citation/reference

Regulations on lighting are addressed in multiple USFWS, Birds Information on lighting and 

guidelines. If a structure is over 200 m, lighting will be FS, BLM, birds: Gehring et al. 2009, 

required by the Federal Aviation Administration (FAA), and OR. Kerlinger et al. 2010, 

but there are specific suggestions for type of lighting Longcore et al. 2008. Horn

to use within USFWS and OR guidelines. From USFWS, et al. (2008) found no 

“Employ only red, or dual red and white strobe, strobe- impact for bats between 

like, or flashing lights, not steady burning lights, to meet lighted and unlighted

FAA requirements for visibility lighting of wind turbines, turbines (lit with steady and 

permanent meteorological towers, and communication strobing aviation 

towers. Only a portion of the turbines within the wind obstruction lights). 

project should be lighted, and all pilot warning lights should 

fire synchronously.” Detailed direction in FS directives as

well. Note: BLM guidelines also recommend minimizing 

lighting to reduce visual disturbance. Wildlife impacts 

are not specifically mentioned.

Keep lighting at both operation and maintenance USFWS, Birds For birds (Gehring et al. 

facilities and substations to the minimum required. BLM, FS, 2009, Kerlinger et al. 2010 

From USFWS: and OR Longcore et al. 2008) 

a. Use lights with motion or heat sensors and switches Kerlinger et al. (2010) 

to keep lights off when not required. found no difference in bird 

b. Lights should be hooded downward and directed to mortalities between turbines 

minimize horizontal and skyward illumination. lit with flashing lights and

c. Minimize use of high-intensity lighting, unlit turbines. Horn et al. 

steady-burning, or bright lights such as sodium vapor, (2008) found no impact for 

quartz, halogen, or other bright spotlights. bats between lighted and 

d. All internal turbine nacelle and tower lighting unlighted turbines (lit with 

should be extinguished when unoccupied. steady and strobing aviation 

USFWS guidelines specify that guidance is for obstruction lights). 

buildings within half a mile of turbine.

Manage vehicles and traffic volumes to reduce USFWS, Wildlife Standard operating

wildlife collisions BLM, procedure.

OR, and WA

a

 Practices are organized by resource, and listed with supporting scientific literature, where applicable.
9

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Description of a Wind Energy Facility

Utility-scale wind turbines (those that can generate greater than 1 MW) installed 

after the 1990s have all been similarly designed with a single tubular tower ranging 

in height from 60 to 100 m, and three rotor blades up to 40 to 50 m in length 

(Kunz et al. 2007b, U.S. Department of Energy 2008) (fig. 2, 3). Current turbine 

rotor blades may reach up to 50 m (power outputs of 3 to 5 MW) (U.S. Department 

of Energy 2008), so that tower plus blade height ranges up to 150 m, taller than a 

40-story building (Kunz et al. 2007b). Over the past 25 years, wind turbine size has 

steadily increased, in part because windspeed increases with the height above the 

ground, enabling larger turbines to produce energy more efficiently. 

Turbines work by converting energy from the moving rotor blades into electrical power in the nacelle, a unit at the top of the tower that houses the converter and 

controls. Sensors on the turbine provide information on windspeed and component 

performance in order to respond to windspeed and regulate the power output and 

rotor speed. The turbine is pointed into the wind by rotating the nacelle around the 

tower. Turbine power output is controlled by changing the “pitch” or angle of the 

blades around their long axis in response to wind. Turbines generally start producing power in winds of 3.5 to 4.0 m per second (m/s) (Arnett et al. 2011, Baerwald et 

al. 2009), reaching maximum power output at about 12.5 to 13.4 m/s (U.S. Department of Energy 2008). The amount of energy available for turbines increases with 

the cube (the third power) of windspeed, meaning that a 10 percent increase in 

windspeed creates a larger (33 percent) increase in available energy. When windspeed becomes too high, at approximately 23 m/s, turbines will “pitch” or “feather” 

the blades to stop rotation and halt power production. Each 1.5-MW turbine may 

produce 4.6 million kilowatt-hours per year, equivalent to electricity needs for 300 

to 900 households, depending on energy consumption (National Wind Coordinating Collaborative 2010). A turbine’s MW rating is the “name-plate” capacity or 

manufacturer’s capacity of a wind turbine to generate electricity. The actual energy 

produced by a turbine will depend on the windspeeds experienced at the site.

Within a wind energy facility, individual turbines are normally arranged in 

a line linked together through underground cables into arrays, then connected to 

the local power grid. Turbines are typically installed in arrays of 30 to 150 (U.S. 

Department of Energy 2008). Although the footprint, or area occupied by a turbine, 

is generally small (usually 2800 to 4050 m2

 per turbine),4 turbines are only part of 

the infrastructure developed for a wind energy facility. The associated buildings,

4

 Strickland, D. 2011. Personal communication. President and senior ecologist, Western 

EcoSystems Technology, Inc., Environmental and Statistical Consultants, 2003 Central 

Avenue, Cheyenne, WY 82001. 

Over the past 25 years, 

wind turbine size has 

steadily increased, 

in part because 

windspeed increases 

with the height above 

the ground, enabling 

larger turbines to 

produce energy more 

efficiently. 
10

general technical report pnw-gtr-863

Figure 2—Operational wind turbines.

Dennis E Schwartz Paul Cryan, U.S. Geological Survey
11

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

roads, electrical transmission lines, or connections to electrical transmission lines 

make up the wider footprint of a wind energy facility. Access roads may be the 

largest infrastructure development for a wind energy facility because each turbine 

requires an access road so that turbines can be serviced. Access roads are used 

by heavy equipment, including cement mixers and cranes, for construction and 

maintenance. Depending upon the project, roads will be a minimum of 3 m wide, 

Figure 3—Construction and maintenance of wind turbines.

Dennis E Schwartz Dennis E Schwartz
12

general technical report pnw-gtr-863

and may extend up to 10 m. In total, the permanent footprint of a wind energy 

facility is approximately 5 to 10 percent of the entire site (USDI Bureau of Land 

Management 2005). The amount of surface disturbance will differ with site 

characteristics such as vegetation and topography. The current trend has been to 

locate wind energy facilities where there are existing transmission lines that can be 

used. In the future, if wind power is to increase significantly, there will need to be 

substantial expansion of transmission systems to deliver wind energy through the 

electrical grid (U.S. Department of Energy 2011, USDI Bureau of Land Management 2005). 

Science Findings: The Effects of Wind Energy Facilities 

on Wildlife

The first wind energy facilities were constructed in the United States in the 1980s 

in California, and concerns about wildlife collisions emerged soon thereafter. The 

wind industry has grown tremendously over the past 10 years, leading to additional 

concerns about habitat alteration. Because it is a new form of land use, there has 

been relatively little research on the impacts of wind energy facilities on wildlife, 

but new studies are continuously emerging. Below, we review the current scientific 

literature on wind energy facilities and wildlife, considering habitat loss and direct 

mortality, in sequence.

Habitat Loss and Modification 

Construction of a wind energy facility causes habitat loss and fragmentation when 

vegetation is removed for infrastructure development, including turbines, buildings, 

roads, and connections from the wind energy facility to the existing electrical transmission lines. Operation of wind turbines and associated human activity may also 

reduce wildlife habitat quality, either negatively affecting resident wildlife populations or displacing populations (Arnett et al. 2008, Kunz et al. 2007b, Kuvlesky et 

al. 2007, Pearce-Higgins et al. 2012). The overall impact of wind energy facilities 

on habitat depends upon the habitat quality and wildlife community prior to facility 

construction (U.S. Fish and Wildlife Service 2012). Although agricultural areas 

can offer significant benefits for some wildlife species, a wind energy facility built 

in an agricultural area will cause less destruction of native vegetation than will a 

facility built in forested vegetation. Similarly, constructing a wind energy facility in 

natural vegetation with low levels of human use will lead to increased human activity, noise, and lighting, whereas an agricultural area may already have significant 

human use and infrastructure. 

Construction of a wind 

energy facility causes 

habitat loss and 

fragmentation when 

vegetation is removed 

for infrastructure 

development, including 

turbines, buildings, 

roads, and connections 

from the wind energy 

facility to the existing 

electrical transmission 

lines.
13

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Most of the habitat loss from wind energy facility construction results from the 

creation of a road network between turbines, which is needed for both construction 

and maintenance. Roads reduce natural vegetation, while introducing disturbance 

in the form of noise, lights, pollution, and human activity (roads also increase direct 

mortality through collisions) (Fahrig and Rytwinski 2009). Prior research shows 

that aquatic organisms may be affected by road construction owing to changes 

in geomorphic processes, including sedimentation during construction and use 

during the life of the road (Gucinski et al. 2001, Switalski et al. 2004, Trombulak 

and Frissell 2000). Beyond the direct changes associated with wind energy facility 

construction and operation, wind energy facilities may also lead to greater indirect 

effects on habitat that play out over longer timeframes, such as introduction of 

invasive species, alteration of fire regimes, and increased predator populations 

(U.S. Fish and Wildlife Service 2012). 

In an operating wind energy facility, new roads and associated human activity, 

along with the noise, lighting, and movement of the turbines combine to modify the 

environment for wildlife. The effects of this habitat modification on wildlife remain 

unclear for many species, as there have been relatively few studies of wildlife after 

wind energy facility operation, with still fewer studies conducted over long timeframes. Most studies of wildlife response to wind energy facility operation have 

been relatively brief, and often focus on specific effects on behavior or abundance, 

rather than the population-level impacts of disturbance (Carrete et al. 2009, Madsen 

and Boertmann 2008). There are far more general studies (i.e., not specific to wind 

energy facilities) of species’ avoidance of roads and traffic disturbances (Fahrig and 

Rytwinski 2009, Gucinski et al. 2001, Trombulak and Frissell 2000). This literature 

on wildlife and roads shows that roads have consistently negative impacts on a 

wide range of taxa, through direct mortality, vegetation alterations, and disturbance 

caused by human activity (noise, lights, traffic motion) (Fahrig and Rytwinski 

2009). Species most affected by direct mortality on roads include reptiles and 

amphibians, as well as some mid-sized and larger mammals with low reproductive 

rates and large movement ranges (although small mammals generally showed either 

neutral or positive impacts) (Fahrig and Rytwinski 2009). 

Habitat loss resulting from noise is often associated with roads, but wind 

turbine noise has also been discussed in the literature on wildlife and wind energy. 

However, while human acceptance of wind turbine noise has been a major area of 

research (Hessler and Hessler 2011), relatively little research has been done specifically on turbine noise impacts on wildlife. Maximum allowed noise for human 
14

general technical report pnw-gtr-863

exposure is generally around the 40 dB(A)5 level (Knopper and Ollson 2011), but 

wildlife are known to be sensitive to noise. Grouse species, in particular, are often 

discussed in the literature about noise (BLM 2005b, Manville 2004). Barber et al. 

(2010) stated that -20 dBA is the level of sound just audible to many species (e.g., 

bats, owls, or foxes). Although species’ responses to noise disturbance will differ, 

bird distribution and physiological responses to sound are documented to occur 

between 40 to 60 dBA (Barber et al. 2010, Reijnen et al. 1996). Data suggest noise 

increases of 3 to 10 dBA correspond to 30- to 90-percent reductions in alerting 

distances for wildlife, respectively (Barber et al. 2010). Only the Forest Service 

guidelines mention a specific threshold for noise, stating not to exceed 10 dB above 

the background noise level “in or near habitat of wildlife known to be sensitive to 

noise during reproduction, roosting, or hibernation; or where habitat abandonment 

may be an issue;” however, guidelines do not provide specific scientific studies 

linked to this threshold (USDA Forest Service, 2011a). Understanding the potential 

effects of turbine noise on wildlife will require additional research (U.S. Fish and 

Wildlife Service 2012), although it remains challenging to isolate noise effects from 

associated disturbances (e.g., isolating turbine noise from the visual stimulation of 

turbine movement). 

Because wind energy facility development has expanded rapidly in recent 

decades, there are still relatively few studies of their effects on wildlife populations 

in the Pacific Northwest region. In this region, concerns about habitat loss and 

alteration owing to wind energy facility development are likely to focus on endangered or high-profile species and habitats of conservation significance, including 

northern spotted owls (Strix occidentalis caurina) and marbled murrelets (Brachyramphus marmoratus) in old-growth forest, and greater sage grouse (Centrocercus 

urophasianus), pygmy rabbits (Brachylagus idahoensis), and ground squirrels 

(Urocitellus spp.) in shrub steppe vegetation. Across the region, land use impacts on 

bull trout (Salvelinus confluentus) and anadromous fishes are also of concern. With 

the exception of sage grouse, discussed below, the effects of wind energy facilities 

on these species have not yet been studied. Below we review the current scientific 

literature on the effects of habitat loss and modification on wildlife, incorporating 

information from the Pacific Northwest when available. 

Birds— 

Among bird species, songbirds and grassland birds are the primary species negatively affected by the disturbance of wind energy facilities and roads (Fahrig and 

5

 A decibel (dB) is a unit of measurement of voltage or other intensity. Decibles are one 

tenth of a bel.
15

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Rytwinski 2009). With wind energy development, grassland birds have been the 

focus of much scientific concern because grassland vegetation has been extensively 

fragmented by other land uses and because grassland birds have experienced significant population declines (greater than other bird groups) (Arnett et al. 2007). 

At the Buffalo Ridge wind site in Minnesota, lower songbird densities observed 

in areas with turbines were thought to result from avoidance of turbines, although 

exact mechanisms are unclear (Leddy et al. 1999, Osborn et al. 1998). While more 

research is needed, available studies suggest that some disturbance or displacement 

may occur for grassland/shrub-steppe species (Arnett et al. 2007). 

Nationally, impacts of wind energy facilities on grouse species are of concern 

because a number of these grassland-dependent species are endangered or declining, and research thus far indicates that grouse are sensitive to anthropogenic 

activity associated with wind energy facilities (Connelly et al. 2000, U.S. Fish and 

Wildlife Service 2012). Greater sage grouse found in the eastern parts of Oregon 

and Washington is a candidate species under the Endangered Species Act (ESA) 

(75 CFR 13910 2010). While impacts of wind energy facilities on sage grouse are 

a management concern, there have been relatively few studies of wind energy 

impacts on sage grouse published in the scientific literature (for review of the 

literature, including unpublished studies, see Johnson and Holloran [2010] and 

Naugle et al. [2011]). Research on sage grouse suggests that roads, transmission 

lines, and areas of oil and gas development and production within 4.8 or 8 km (or 

more) of active sage grouse leks (breeding grounds) may have significant negative 

impacts for grouse populations, by reducing fecundity (Connelly et al. 2000, Harju 

et al. 2010, Naugle et al. 2011, Walker et al. 2007) and yearling survival (Holloran 

et al. 2010). Disturbances that cause males and females to abandon leks include 

development of power lines and roads, traffic noise, other human activity and 

noise, and raptors perching on power lines, as reviewed by Naugle et al. (2011). As 

development continues, impacts on sage grouse appear to intensify: breeding is 

disrupted with lower densities of energy development, and populations decrease and 

avoid areas with higher levels of development (Naugle et al. 2011). Changes in sage 

grouse populations may emerge in complex ways over time as impacts to breeding 

and yearlings cause lagged population responses to development and development 

intensifies over time (Harju et al. 2010, Holloran et al. 2010). Lastly, other types 

of energy development that result in large-scale manipulation or disturbance of 

surface water, such as coalbed methane extraction, have also been associated with 

an increase in West Nile virus among sage grouse, as the additional standing water 

increases mosquito populations (Naugle et al. 2011). Wind energy development uses 

some water during construction, but does not require standing water during wind 

Nationally, impacts 

of wind energy 

facilities on grouse 

species are of concern 

because a number 

of these grasslanddependent species 

are endangered or 

declining, and research 

thus far indicates that 

grouse are sensitive to 

anthropogenic activity 

associated with wind 

energy facilities.
16

general technical report pnw-gtr-863

turbine operation, so West Nile virus should be less of a concern in wind energy 

operations.

Several studies have discussed habitat avoidance after wind energy facility 

establishment. A wind energy facility in an agricultural area of the Midwest showed 

a 47 percent decrease in raptor abundance after establishment of a facility (Garvin 

et al. 2011). In Norway, researchers found that vacant territories near wind turbines 

led to decreased breeding success for white-tailed eagles (Haliaeetus albicilla) 

(Dahl et al. 2012). Researchers were not able to differentiate vacancies caused by 

disturbance or mortality, but showed that vacant territories remained over a 10-year 

study period (i.e., territories were not recolonized), suggesting that wind turbine 

operation led to habitat loss. 

In coastal areas and wetlands, waterbirds, including flocking geese, swans, 

ducks, and waders are also considered sensitive to wind energy facility development, generally avoiding wind energy facilities by distances of 100 m or more 

(Madsen and Boertmann 2008, Masden et al. 2009a). Studies of long-term impacts 

show mixed results: Madsen and Boertmann (2008) found that pink-footed geese 

(Anser brachyrhynchus) in Denmark reduced their avoidance to relatively smallscale wind energy facilities over an 8-year period, while in a meta-analysis of 

wind energy facilities, Stewart et al. (2007) found that decreases in bird abundance 

remained over time. There are concerns that migratory birds face increasing 

energetic consequences of avoiding wind energy facilities as facilities expand along 

migratory routes. The energetic costs of avoiding one wind energy facility are 

small in comparison to a long-distance migratory event, but the population impacts 

of additional energy costs incurred by avoidance remain unknown (Masden et al. 

2009b). In the Pacific Northwest, the marbled murrelet is a coastal species listed as 

endangered under ESA, but there are not yet any operating wind energy projects 

within marbled murrelet range, so it is unclear how or if marbled murrelets may 

avoid wind turbines (Cooper and Sanzenbacher 2006, Nations and Erickson 2009, 

Nelson et al. 2009).

Nonvolant mammals— 

Regarding mammals, there have only been limited studies examining habitat loss 

and response to wind energy facilities. One study of elk (Cervus canadensis) during construction and operation of a wind energy facility in Oklahoma demonstrated 

that resident elk showed no significant changes in home range or dietary quality 

(Walter et al. 2006). Elk freely crossed the gravel roads developed for the facility. 

However, previous studies of road networks have shown that elk tend to avoid large 

roads, with avoidance increasing with human activity (Wisdom et al. 2000). Elk 

are also known to be sensitive to human activity away from roads, such as off-road 

There are concerns 

that migratory 

birds face 

increasing energetic 

consequences 

of avoiding wind 

energy facilities as 

facilities expand along 

migratory routes. 

The energetic costs 

of avoiding one wind 

energy facility are 

small in comparison 

to a long-distance 

migratory event, but 

the population impacts 

of additional energy 

costs incurred by 

avoidance remain 

unknown.
17

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

recreation (Naylor et al. 2009). Other forms of energy development, including oil 

and gas development, have been shown to affect ungulates. In one study, mule deer 

(Odocoileus hemionus) avoided areas with energy development, and did not habituate to these areas over a 3-year period, so that indirect habitat loss caused by human 

activity was far larger than habitat loss resulting from direct vegetation modification during well-pad development (Sawyer et al. 2006). 

Small mammals are generally thought to be more resilient in the face of infrastructure development. One study of California ground squirrels showed that animals were able to live among turbines in a wind energy facility (Rabin et al. 2006). 

However, researchers suggested that the noise of operating turbines led animals to 

alter their behavior: in a comparison between a control and a turbine site, animals at 

the turbine site showed greater vigilance and antipredator behavior, which authors 

concluded was an attempt to compensate for the difficulty of responding to auditory 

communication within the wind energy facility site. Similar to many other studies 

of noise disturbance, this study examined behavior between a wind energy facility 

site and a control site, and thus was not able to isolate specific features of turbine 

noise from other visual or auditory disturbances in the wind turbine site. 

Bats— 

The effects of habitat modification by wind energy development on bats are not well 

understood, but most concerns center around changes in forest vegetation (National 

Research Council 2007). Wind energy development in forested areas may influence the availability of tree roosts through vegetation modification. Alternatively, 

researchers have also suggested that because bats use edge habitat between forest 

and nonforested areas, wind energy development may lead to higher bat activity at 

the site, and more collisions.

Direct Mortality and Behavior

In addition to habitat modifications, wind energy facilities may directly affect wildlife populations through collision with turbines. Wind turbine collision issues have 

been most well-studied in birds, particularly raptors and migratory birds, but over 

the past decade, bat mortality at wind energy facilities has emerged as a significant 

conservation issue, so that “what was once a bird issue has become a bat issue” as 

well (Barclay et al. 2007). 

Collision issues are essentially the opposite of displacement: species that can 

tolerate or are even attracted to wind energy facilities are at risk of increased collision mortality, while species that avoid or are displaced by wind energy facilities 

lose habitat, but do not risk collisions. For example, territorial bird species, such as 

raptors, may have fewer issues with displacement by wind energy facilities, but then 

Collision issues are 

essentially the opposite 

of displacement: 

species that can 

tolerate or are even 

attracted to wind 

energy facilities are 

at risk of increased 

collision mortality, 

while species that avoid 

or are displaced by 

wind energy facilities 

lose habitat, but do not 

risk collisions.
18

general technical report pnw-gtr-863

suffer higher incidence of collisions (Carrete et al. 2009). Conversely, birds that are 

sensitive to wind energy sites (e.g., grassland birds), and thus avoid them may be 

less prone to collisions with turbines (Leddy et al. 1999, Osborn et al. 1998). The 

relationship between the two potential responses (avoidance or collision) may also 

differ over time (e.g., birds may habituate to a disturbance, or might grow intolerant 

over time as tolerant individuals are killed and not replaced) (Madders and Whitfield 2006). In addition, risk of collision from wind turbines is not the only source 

of direct mortality at wind energy sites. For example, although sage grouse are not 

considered highly at risk from direct mortality with moving turbines, collisions 

with power lines and vehicles will increase mortality of birds in leks (Naugle et al. 

2011).

While direct mortality from collisions is commonly discussed in the wind 

energy literature, bird mortality caused by collisions with wind turbines is likely 

much less than collisions with other infrastructure, such as buildings, high-tension 

lines, and communication towers. Estimates of the latter collisions are difficult to 

determine, owing to multiple sources of uncertainty, but are thought to be in the 

hundreds of millions, while total estimates of birds killed by wind turbines are 

much lower (National Research Council 2007). There is less background information on bat collision rates with other infrastructure, but Johnson et al. (2003) summarize the literature and report relatively low levels of mortality from collisions 

with other infrastructure. However, bat fatalities from turbines occur in addition 

to a number of other threats to bat populations, including white-nose syndrome, a 

rapidly spreading and highly fatal fungal disease that originated in the Northeastern United States (Frick et al. 2010). Bats are also relatively slow reproducing 

animals, leading to concerns about the ultimate population-level impact of direct 

mortality from wind turbines (Kunz et al. 2007b).

Because the likelihood of collisions depends upon complex interactions among 

site characteristics, turbine characteristics, and animal behavior (Kuvlesky et al. 

2007, Madders and Whitfield 2006, Stewart et al. 2007), below we discuss each 

factor for both birds and bats. We consider only the impacts of wind turbines, and 

not associated transmission lines. Although transmission lines result in additional 

mortality for bird species through collisions and electrocution, there are existing 

guidelines on minimizing power line impacts on wildlife (Avian Power Line Interaction Committee 2006) (referenced in current state and federal guidelines (table 

1), and power lines are not unique to wind energy facilities. Similarly, management 

practices for energy corridors have been broadly addressed by the federal Westwide 

energy corridor planning process (USDE and USDI 2008). 
19

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Birds— 

Concerns about bird collisions first emerged at wind facilities built in the 1980s 

in California, where high densities of resident and migratory raptors and smaller 

turbines (14 to 43 m) with an older “lattice” tower design contributed to an estimated annual fatalities of 1,127 raptors and 2,710 birds (National Research Council 

2007, Smallwood and Thelander 2008). Subsequent studies from other parts of the 

country with more modern turbines have found lower bird fatalities (Barclay et 

al. 2007, Kuvlesky et al. 2007). The National Research Council (2007) compiled a 

number of unpublished studies to examine wildlife collisions, using only data from 

studies that were longer than a year in duration and used standardized mortality 

searches, including correcting for carcass decomposition, scavenging, and observer 

search efficiency. This review found that fatalities at wind farms ranged from 0.95 

birds/MW/year to 11.7 birds/MW/year (National Research Council 2007). However, 

subsequent studies at the site with the high estimate (Buffalo Mountain, Tennessee) 

lowered bird fatality estimates to 1.1 birds/MW/study period (Young and Poulton 

2009). The second highest estimate of bird fatality compiled by the National 

Research Council (2007) was 5.93 birds/MW/year, from Buffalo Mountain, 

Minnesota. Research indicates that passerines (songbirds), especially nocturnal migrants, are the most frequent collision fatalities across sites. Raptor research in both 

the United States and Europe shows that raptor fatalities do not follow directly from 

raptor abundance, because some species-specific behaviors such as flying in rotorswept areas result in higher collision rates for less common species (de Lucas et al. 

2008, Garvin et al. 2011). 

Understanding the population-level effects of these collisions requires information on species abundance and distribution, as well as the combined effects of other 

wind energy facilities. At the individual facility level, estimates of passerine fatalities, from published and unpublished studies, are often below five animals/turbine/

year, a level that is thought to be insignificant for populations unless a species is 

threatened or in decline (Kuvlesky et al. 2007). Raptor populations, in contrast, are 

thought to be more severely affected by collision mortality because they are longer 

lived with lower reproductive potential (Carrete et al. 2009). However, population 

stability is difficult to assess and may require information on dispersal and links 

between wildlife populations. For example, a 7-year study of the golden eagle 

(Aquila chrysaetos) population at Altamont Pass Wind Resource Area in California 

documented 42 fatalities from wind turbine strikes (Hunt 2002). Authors concluded 

that overall population growth was stable, but likely was not producing a surplus of 

“floater” animals without territories that could buffer the population from additional losses of habitat or increased mortality. More information on links between 

Understanding the 

population-level effects 

of these collisions 

requires information on 

species abundance and 

distribution, as well as 

the combined effects 

of other wind energy 

facilities.
20

general technical report pnw-gtr-863

this population and other populations in the region would help determine population 

stability (Smallwood and Thelander 2008). 

In the Pacific Northwest, there is little peer-reviewed information on avianwind energy facility collisions, but a number of efforts have compiled technical 

reports that followed standard search protocols and methods for estimating mortalities in the Columbia Plateau ecoregion, the roughly triangular shaped, that and 

agricultural region centered around the Columbia River, reaching from the Dalles, 

Oregon to Lewiston, Idaho to Okanogan, Washington near the Candian border. 

Much of the wind energy development in Oregon and Washington is concentrated 

in this region. These wind energy facilities are all located in grassland or agricultural areas. In the most recent synthesis, raptor mortality was on average 0.08/

MW/year in the Columbia Plateau ecoregion, and all bird mortality 2.36/MW/year 

(Johnson and Erickson 2011). At individual wind energy sites, raptor mortality 

ranged from 0/MW/year to a maximum of 0.29/MW/year, while overall bird mortality ranged from 0.06/MW/year to 7.72/MW/year (Johnson and Erickson 2011). 

Bird fatalities were predominantly passerines (68 percent), with 13 percent 

upland gamebirds, 9 percent raptors, and the remaining 10 percent composed of 

doves/pigeons, waterbirds, vultures, and other species. The most frequently killed 

passerine was the horned lark (Eremophila alpestris), making up 30.8 percent of 

all bird fatalities. Horned larks are the most abundant songbird observed during 

preconstruction bird-use surveys at these sites. Raptor mortality ranged from 0 

to 0.29 birds/MW/year, with kestrels (Falco spp.) and red-tailed hawks (Buteo 

jamaicensis) as the most commonly killed species (29 percent and 22 percent of all 

raptors, respectively). In one well-publicized incident, the first golden eagle fatality 

from a wind turbine in Washington state was reported in May 2009 (Associated 

Press 2009). In comparison to other regions of the country, the Pacific Northwest 

had more coots and rails and gamebirds among fatalities, and fewer passerines 

(National Research Council 2007). Authors conclude that anticipated cumulative 

effects of current and proposed wind energy facilities will be low on the common 

grassland and agricultural species that are the majority of fatalities in the Columbia 

Plateau ecoregion (Johnson and Erickson 2011). For less common species, authors 

use survey data from the Breeding Bird Survey and available information on natural mortality rates to also conclude that for the Columbia Plateau ecoregion, more 

rarely killed species are also unlikely to incur significant population-level impacts 

from wind energy development (Johnson and Erickson 2011).

A number of studies have attempted to document marbled murrelet activity 

patterns in wind energy development sites (Cooper and Sanzenbacher 2006, 

Nations and Erickson 2009). Using these activity patterns to predict potential 
21

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

fatalities and the population-level impacts of such fatalities is complex (Nations and 

Erickson 2009, Nelson et al. 2009). At the Radar Ridge wind energy development 

site in Washington, Nations and Erickson (2009) used a wind turbine collision 

model to predict that large wind turbines, operating continuously, would result in 

annual fatalities of 0.74 marbled murrelets per year, leading them to conclude that 

fatalities over the life of the project were expected to be low. In contrast, Nelson et 

al. (2009) examined the available data on marbled murrelet use at the site and concluded that the project was likely to have an adverse effect on marbled murrelets. 

Part of the uncertainty in predicting mortality rates stems from collision models 

with incomplete knowledge of bird behavior. Without site-specific and speciesspecific information on birds’ avoidance behaviors, the ability to estimate mortality 

rates through collision models may be limited (Chamberlain et al. 2006).

Site topography and characteristics—A site’s topography and ecological features 

often determine bird use, and may also directly influence collision mortality. For 

example, in a review of technical reports, Drewitt and Langston (2006) suggested 

that birds’ responses to topography may include soaring along ridges or lowering 

flight height when along the coast or when crossing a ridge, which then increases 

collisions. Placing wind energy facilities in areas commonly used by raptors, such 

as slopes of hills or ridges, is thought to increase mortalities (Kuvlesky et al. 2007), 

although these are also the areas with the greatest wind resources. In Spain, high 

raptor morality resulted after wind energy facilities were constructed along a topographic bottleneck, an area where migrating birds are funneled by the surrounding landscape (e.g., mountains, rising winds) (Barrios and Rodriguez 2004). For 

migratory birds, available evidence suggests that birds migrate at relatively high 

elevations (above turbines), but may be vulnerable when at lower elevations owing to weather or when landing or taking off (Arnett et al. 2007, National Research 

Council 2007). In general, the effect of topography on bird migration remains 

poorly understood (Arnett et al. 2007, National Research Council 2007). 

Researchers are also interested in how the layout design of the wind energy 

facility may also influence mortality within a site (Kuvlesky et al. 2007), but it is 

challenging to study different turbine configurations in well-designed comparisons, 

and there has been relatively little research on turbine configuration. Studies have 

found that mortalities may be concentrated in space within wind energy facilities, 

or may be more evenly distributed (e.g., Barrios and Rodriguez 2004). Researchers 

propose that variation in spatial pattern of mortalities results both from topographic 

features and variation in species behavior (Barrios and Rodriguez 2004). Ecological 

modifications of the site after construction will also influence direct mortality. For 

example, raptor populations may have increased in some cases around wind energy 
22

general technical report pnw-gtr-863

facilities because habitat alterations increased prey populations, ultimately leading 

to more collisions (Smallwood et al. 2007).

Turbine characteristics—Researchers have suggested that characteristics of the 

turbine, such as turbine height, structure, blade length, and lighting, may determine 

wildlife mortality (Kuvlesky et al. 2007), but results thus far show relatively limited 

impacts of turbine features. In a review of more than 30 studies from wind energy 

facilities (many of them unpublished reports), Barclay et al. (2007) found that the 

size of the rotor-swept area did not alter mortality rates, and that the per-turbine 

fatality rate for birds remained constant with increasing height. Although turbines 

are increasing in size, in many cases, migrating birds still tend to pass at higher 

elevations (Johnson and Erickson 2011), unless weather conditions and topographical conditions combine to lower birds’ flying elevations (National Research Council 

2007). Older style “lattice” type towers have been largely replaced by tubular towers to discourage birds from perching on towers, although some studies show no 

significant differences in mortality between lattice and tubular towers (Barrios and 

Rodriguez 2004, Smallwood et al. 2007). Lighting on turbines and other structures 

has been discussed as a factor increasing bird mortality among nighttime migrants 

since the 1950s, but recent research suggests that wind towers with flashing lights 

have low mortalities of migrants in comparison to communication towers, which 

are generally taller, often lit with some steady (nonflashing) lights, and have more 

infrastructure in the form of guy wires to support towers (Gehring et al. 2009, 

2011; Kerlinger et al. 2010). Research from communication towers showed that 

steady burning (nonflashing) lights increase mortalities (Gehring et al. 2009), so 

researchers have recommended that only flashing lights be used in wind turbine 

sites (Kerlinger et al. 2010). A meta-analysis of technical reports from wind energy 

facilities found no significant difference in mortalities among turbines lit with flashing lights and those that are not lit (not all turbines in a wind energy facility are lit 

depending on their physical spacing) (Kerlinger et al. 2010). Recommendations and 

more specific information on lighting are included in federal and state guidelines 

(table 1).

Bird behavior—Turbine collisions are fundamentally a behavioral issue, with species’ different tolerances of turbines leading to variable mortality rates among species. Researchers have documented a number of ways in which species’ behavior 

alters their risk of collision mortality. Birds’ vulnerabilities to collision are often 

linked to species-specific flight behavior (Barrios and Rodriguez 2004, de Lucas et 

al. 2008, Drewitt and Langston 2006). As discussed above, weather conditions and 

topography may alter bird behavior, and lead to collisions. Bird activity may also 

differ between sex and age, leading to different collision mortalities for different 
23

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

subgroups of a population (e.g., Stienen et al. 2008). Bird mortality rates often differ seasonally (e,g., most passerine fatalities in North America occur between April 

and October) (Arnett et al. 2007). Seasonal variation in fatalities appear to result 

from seasonal variations in bird populations, behavior, and migration activity, as 

well as variation in weather (e.g., Barrios and Rodriguez 2004, Osborn et al. 1998).

While it is unclear why species approach, or do not avoid, turbines, these avoidance rates are critical to better understand and predict avian mortality. Models that 

attempt to estimate collision risk by combining information on the structure and 

operation of turbines with bird size and flight show that small variations in avoidance rates (often estimated as greater than 0.95 in case studies) lead to relatively 

large increases in predicted collisions (Chamberlain et al. 2006). Because avoidance 

rates are often calculated based on the number of mortalities observed divided by 

the number of birds flying through the turbines’ rotor-swept area, these rates may 

be subject to observer error and challenges of surveying bird behavior at high elevations at wind energy sites (Chamberlain et al. 2006). 

Bats—

The impact of wind turbines on bats has increasingly been studied in North 

America over the past 5 to 10 years, spurred by reports of substantial bat mortalities from the mid-Atlantic highlands (Maryland, Pennsylvania, Virginia, and West 

Virginia). For example, one of the earliest studied facilities, the Mountaineer Wind 

Energy Center in West Virginia, had an estimated 1,400 to 4,000 bat deaths annually (>30 fatalities MW-1•year

-1) (Arnett et al. 2008). Substantial bat fatalities have 

also been reported in the Southeast and Midwest (Arnett et al. 2008, Kunz et al. 

2007b), and bat fatalities may outnumber bird fatalities in some areas by 10 to 1 

(Barclay et al. 2007). Arnett et al. (2008) reviewed 21 studies (some peer-reviewed) 

from 19 different wind energy facilities across the United States and Canada and 

found that tree-roosting species accounted for 75 percent of documented fatalities, 

with hoary bats (Lasiurus cinereus) comprising half of all fatalities (Arnett et al. 

2008). Tree-roosting species are also referred to as migratory species: hibernation 

alone may not be sufficient to allow these bats to survive cold winters, and so they 

undertake long-distance migration to warmer climates where hibernation in trees is 

more likely to be successful (Popa-Lisseanu and Voigt 2009). Although background 

information on bat populations and activity is often lacking, evidence thus far suggests that the species composition of wind turbine mortality does not directly correspond to species’ abundance at sites (Cryan and Barclay 2009, Jain et al. 2011). 

Fatalities among bats occur as a result of direct collisions with rotor blades, 

and potentially as the result of barotrauma, the injuries caused when the motion of 

While it is unclear why 

species approach, or 

do not avoid, turbines, 

these avoidance rates 

are critical to better 

understand and predict 

avian mortality. Models 

that attempt to estimate 

collision risk by 

combining information 

on the structure and 

operation of turbines 

with bird size and 

flight show that small 

variations in avoidance 

rates lead to relatively 

large increases in 

predicted collisions.
24

general technical report pnw-gtr-863

turbine blades causes rapid air pressure reduction. Blade tips in modern turbines 

rotate at speeds of 55 to 80 m/s, creating pressure drops of 5 to 10 kilopascals, 

which is sufficient to cause significant damage in mammals (Baerwald et al. 

2008). Birds do not appear to suffer from barotrauma, likely because they have 

compact, rigid lungs and stronger pulmonary capillaries (Baerwald et al. 2008). 

The relative roles of barotrauma and other traumatic injury in causing mortality is 

an active area of investigation. At a wind energy facility in Alberta, Canada, up to 

90 percent of bat fatalities showed internal hemorrhaging, but only half of all bat 

fatalities showed external injuries, leading authors to suggest that barotrauma is a 

significant cause of wind energy fatalities (Baerwald et al. 2008). However, a study 

from Wisconsin reported barotrauma and direct collisions were not always discernible (Grodsky et al. 2011) and Rollins et al. (2012) concluded that approximately 5 

percent of wind energy mortalities could be attributed to barotrauma alone (using 

ruptured eardrums as the marker for barotrauma). Additional research on the 

relationship between collisions, pressure differentials, and mortalities will further 

refine our understanding of bat fatalities, but in this report, we consider the term 

collision or direct mortality to include physical injuries or fatalities resulting from 

interaction or proximity to turbines.

In the Pacific Northwest, little information exists on bat populations, migratory patterns, or wind energy facility impacts. Forest-dwelling migratory species 

found in the region include the hoary bat and the silver-haired bat (Lasionycteris 

noctivagan). Other bat species present in the region include little brown myotis 

(Myotis lucifugus) and big brown bat (Eptesicus fuscus). At present there are no 

peer-reviewed studies examining the rates of bat mortality in Oregon and Washington, but Johnson and Erickson (2011) summarized technical reports on bat impacts 

in the Columbia Plateau region. They found bat mortality ranged from 0.27 bats/

MW/year to 3.78/bats/MW/year (Young and Poulton 2009), which is lower than 

high mortalities reported in the East and upper Midwest (Arnett et al. 2008, Kunz 

et al. 2007b). Silver-haired and hoary bats made up nearly all of the fatalities (48 

percent and 46 percent, respectively) (Johnson and Erickson 2011). Without more 

information on the relative abundance of different species prior to wind energy 

development, and the overall population abundance and distribution of bat species, 

it is challenging to evaluate the population-level impacts, or the cumulative effects 

of multiple wind-energy developments. 

Site topography and characteristics—Among bats, no clear relationships between 

fatalities and habitat or topographic characteristics have been detected (Arnett et 

al. 2008, Stewart et al. 2007), although one recent study in Oklahoma found higher 

mortality rates concentrated at several turbines within a facility (Piorkowski and 

In the Pacific 

Northwest, little 

information exists 

on bat populations, 

migratory patterns, or 

wind energy facility 

impacts.
25

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

O’Connell 2010). In this case, researchers suggested that mortality might result 

from a landscape feature (eroded ravine) serving as a conduit for daily movements 

of bats from a maternity colony (Piorkowski and O’Connell 2010). Otherwise, 

previous reviews have concluded that mortalities tended to be evenly distributed 

throughout wind energy facilities (Arnett et al. 2007, National Research Council 

2007). There are concerns that wind energy facilities themselves modify habitat 

in a manner that attracts bats. The forest edges created by access roads may create 

hotspots of bat activity because edges enhance bat foraging for insects (Arnett et al. 

2008, Stewart et al. 2007). 

Turbine characteristics—Bat fatalities at wind energy facilities increase exponentially with wind turbine height, with the highest mortalities experienced with 

turbines taller than 65 m (Barclay et al. 2007). Within individual turbine sites, bats 

appear to be more active within the rotor-swept medium elevations than below the 

rotor blades, with bat sightings six times more common within rotor-swept areas (29 

to 111 m) than below rotor blades (<29 m) (Horn et al. 2008). Although researchers have raised concerns about turbine lighting attracting insects and increasing bat 

collisions, lighting did not appear to affect the incidence of foraging bats around 

turbines in one study in West Virginia (Horn et al. 2008). A recent study suggested 

that certain turbine colors attracted more insects, in turn leading to a concentration 

of bats (Long et al. 2011). 

Bat behavior—Behavioral responses to weather patterns and seasonal behavior are 

thought to play an important role in determining bat presence and fatalities (Cryan 

and Barclay 2009, Weller and Baldwin 2012). Collisions are a concern only when 

bats are active, generally from March or April through November for species that 

hibernate during the winter. However, tree-roosting species migrate to avoid cold 

weather, and in warmer climates, bats are more likely to be periodically active during the winter. Seasonally, the highest fatalities are reported during late summer 

and early fall when bats are migrating, with fewer fatalities during the spring migration (Kunz et al. 2007b). In general, low mortalities among bats have been documented during the summer maternity season, but the wind energy facilities studied 

were in open habitat such as cropland or shrub steppe, where forest-dwelling species are not expected to concentrate during maternity season (Arnett et al. 2008). A 

study of a wind energy facility adjacent to two large breeding colonies (2 million 

bats) of Brazilian free-tailed bats in Oklahoma found that over 80 percent of all bat 

mortalities were Brazilian free-tailed bats, and that approximately 60 percent of all 

bats killed were female, suggesting that bats in breeding colonies are vulnerable to 

wind energy facilities (Piorkowski and O’Connell 2010). 
26

general technical report pnw-gtr-863

Within a site, bat activity may follow weather and insect activity. A study in 

southern California found that bats were more likely to be present at turbines when 

windspeeds were lower and temperatures higher, although including date and moon 

illumination also helped predict bat presence (Weller and Baldwin 2012). A study 

at the Mountaineer Wind Energy Facility in West Virginia found a significant 

correlation between insect and bat activity, suggesting that bats may be attracted to 

patches of insects (Horn et al. 2008). In this study, bat activity and fatalities peaked 

in the hours after sunset when insects were most active (Horn et al. 2008). Bat 

fatalities are also higher during periods of low windspeed, when insects are thought 

to be most active (Arnett et al. 2008). Weather patterns, such as low or heavy cloud 

cover, or thermal inversions, may cause bats to alter their flight patterns, increasing 

fatalities (Kunz et al. 2007b).

There have also been persistent questions about bat species’ behavior and if 

bats show an attraction to wind turbines (Cryan and Barclay 2009). If bats’ occurrence at wind energy facilities is coincidental, meaning fatalities occur where bat 

populations and turbines happen to overlap, populations might be more susceptible 

when migrating owing to migrants’ clumped distribution or some other aspect of 

migratory behavior (e.g., flying higher than nonmigrants, or perhaps migrating bats 

are less likely to echolocate) (Cryan and Barclay 2009). In contrast, researchers 

have suggested that a number of wind energy facility features may attract bats. At 

wind energy facility sites, bats have been observed investigating the turbines, and 

alighting on turbines and monopoles (Horn et al. 2008). In one behavioral study, 

researchers documented that bats were struck by turbines during foraging and 

exploratory behavior, not as a result of straight-line flight through the wind facility (Horn et al. 2008). Lights, the sound of moving turbines, the motion of turbine 

blades, novel vegetation such as forest edges created by turbines or roads, insect 

aggregations that occur around wind energy facilities, or an attraction to turbines 

as potential roosts, mating, or gathering sites have all been suggested as factors that 

may attract bats to wind energy facilities (Cryan and Barclay 2009). 

Best Management Practices to Minimize Effects of 

Wind Energy Facilities on Wildlife

Federal laws that pertain to wind energy and wildlife issues include the Migratory 

Bird Treaty Act, Bald and Golden Eagle Protection Act, Endangered Species Act, 

and National Environmental Policy Act, as well as relevant sections of the Clean 

Water Act and the use of aircraft warning lights as required by the Federal Aviation 

Administration (Arnett et al. 2007). Given concerns about wildlife habitat loss and 

direct mortality, there have been a number of efforts to expand beyond the current 
27

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

regulation and develop voluntary guidelines and best management practices for 

wind energy development. The USFWS land-based wind energy guidelines are the 

main national source for voluntary guidelines to help developers collect information, quantify the possible risks of wind energy projects to species of concern and 

their habitats, and evaluate these risks to make siting, construction, and operation 

decisions (U.S. Fish and Wildlife Service 2012). These are the primary guidelines 

for wind energy developers on federal and private land, and are intended to complement other federal law and policy that directs the siting and development of wind 

energy projects on federal lands.

The USFWS guidelines emerged over time, with an interim set of guidelines 

issued in 2003. Following public comment on the 2003 guidelines, the Secretary of 

the Interior created the Wind Turbine Guidelines Advisory Committee under the 

Federal Advisory Committee Act. This committee worked for more than 2 years 

to submit final recommendations to the Secretary of the Interior on March 4, 2010 

(U.S. Fish and Wildlife Service 2011c). An internal working group at USFWS then 

used these recommendations to develop the USFWS draft land-based wind energy 

guidelines, which underwent two revisions: the first draft was released February 

8, 2011, for a 90-day public comment period, and the second revision was released 

July 12, 2011, for a 21-day public comment period. Final guidelines were released in 

March 23, 2012. Our discussion below is based on the final guidelines. 

The guidelines are intended to “promote compliance with relevant wildlife 

laws and regulations; encourage scientifically rigorous survey, monitoring, assessment, and research designs proportionate to the risk to species of concern; produce 

potentially comparable data across the Nation; mitigate, including avoid, minimize, 

and compensate for potential adverse effects on species of concern and their habitats; and improve the ability to predict and resolve effects locally, regionally, and 

nationally” (U.S. Fish and Wildlife Service 2012, p. 1). Guidelines are voluntary, 

and although individuals and companies cannot be absolved of their responsibilities 

under the Migratory Bird Treaty Act and Bald and Golden Eagle Protection Act, 

the USFWS does regard “a developer’s or operator’s adherence to these guidelines, 

including communication with the Service, as appropriate means of identifying 

and implementing reasonable and effective measures to avoid the take of species 

protected under the Migratory Bird Treaty Act and Bald and Golden Eagle Protection Act” (U.S. Fish and Wildlife Service 2012, p. 6). 

The USFWS guidelines rely upon a tiered approach to iteratively evaluate risks 

and minimize the effects of a wind energy development project to fish, wildlife and 

their habitats, through an adaptive management framework. The first three tiers 

deal with site selection and planning and the last two with postconstruction monitoring and research:

The USFWS land-based 

wind energy guidelines 

are the main national 

source for voluntary 

guidelines to help 

developers collect 

information, quantify 

the possible risks of 

wind energy projects 

to species of concern 

and their habitats, 

and evaluate these 

risks to make siting, 

construction, and 

operation decisions.
28

general technical report pnw-gtr-863

Tier 1–Preliminary site evaluation (landscape-scale screening of potential sites)

Tier 2–Site characterization (broad characterization of one or more potential 

project sites)

Tier 3–Field studies to document site wildlife and habitat and predict project 

impacts

Tier 4–Postconstruction studies to estimate impacts

Tier 5–Other postconstruction studies and research

Early communication and use of these guidelines during a wind project’s 

development is intended to ensure the greatest range of development and mitigation 

options. As a project progresses through these tiers, developers will formulate a 

Bird and Bat Conservation Strategy, to explain their studies, analyses, and reasoning while moving through tiers. The USFWS recommends that projects already 

under development or in operation implement those portions of the guidelines 

relevant to the current phases of the project. Projects that are already operational are 

therefore advised to confer with the USFWS about the postconstruction monitoring 

and research tiers (U.S. Fish and Wildlife Service 2012, p. 4). The tiered approach is 

described in the guidelines as a system to “lead to the appropriate amount of evaluation in proportion to the anticipated level of risk that a project may pose to species 

of concern and their habitats” (U.S. Fish and Wildlife Service 2012, p. 6). Study 

plans and the duration and intensity of study efforts should be tailored specifically 

for each unique site and the potential for significant adverse impacts on species of 

concern and their habitats (U.S. Fish and Wildlife Service 2012, p. 6). 

In addition to the wind energy guidelines, USFWS released draft guidelines to 

reduce the impacts of wind development on eagles (U.S. Fish and Wildlife Service 

2011a). Draft eagle guidelines provide “a national framework for assessing and 

mitigating risk specific to eagles through development of eagle conservation plans 

and issuance of programmatic incidental takes of eagles at wind turbine facilities” 

(U.S. Fish and Wildlife Service 2012, p. 3). These eagle guidelines are intended to 

be used in concert with the broader USFWS guidelines. We focus on these more 

general land-based wind energy guidelines (U.S. Fish and Wildlife Service 2012) 

to provide a comprehensive overview of guidelines and best management practices 

recommended by USFWS, but eagle guidelines provide more specific information 

for developers. The final Eagle Conservation Plan guidance will be released to the 

public through the USFWS Web site.

Other federal and state agencies have also developed guidelines and best 

management practices. The BLM underwent a large-scale planning process that 

issued wind energy best management guidelines through a record of decision in 
29

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

2005 (USDI BLM 2005b). These guidelines are general in scope, with site-specific 

planning processes intended to further consider site configuration, monitoring 

program requirements, and appropriate mitigation measures (USDI BLM 2005). 

Forest Service directives are laid out in two documents, one dealing with wind 

energy siting and permitting, and a separate document dealing with wildlife monitoring at wind energy sites (USDA Forest Service 2011a, 2011b). These directives 

closely follow past literature, BLM’s guidelines, as well as USFWS guidelines, and 

refer readers to these other references throughout the directives. Lastly, Oregon 

and Washington also have voluntary guidelines with content similar to the national 

USFWS guidelines, which may also be of interest to land managers in the Pacific 

Northwest. Below, we present the federal and state recommendations for each phase 

of a wind energy facility development: site selection and preparation, construction 

and operation practices, and postconstruction monitoring. We also present a summary of best management practices, with each practice listed under the potential 

threat (habitat loss or direct mortality), cross-referenced to the relevant scientific 

literature (table 1).

Site Selection 

The primary management strategy to avoid or minimize the effects of habitat loss 

and direct collisions is to place wind energy facilities away from species of concern 

and areas of high wildlife value. The federal guidelines and those for Oregon and 

Washington all emphasize the best placement of wind turbines as the primary 

method to protect wildlife (Oregon Columbia Plateau Ecoregion Wind Energy 

Taskforce 2008, U.S. Fish and Wildlife Service 2012, USDA Forest Service 2011a, 

USDI BLM 2005b, Washington Department of Fish and Wildlife 2009).

In USFWS guidelines, Tier 1, or preliminary evaluation/screening of potential 

sites, is described as the stage when developers first examine a broad geographic 

area and conduct a preliminary evaluation of the general ecological context of a 

potential site or sites. Developers are encouraged to work with the USFWS during 

Tier 1, with this assessment also serving as preparation for future work with federal, 

state, tribal, and other local agencies. This first screening process allows developers 

to identify areas of high sensitivity due to “the presence of: 1) large blocks of intact 

native landscapes; 2) intact ecological communities; 3) fragmentation sensitive species’ habitats; or 4) other important landscape-scale wildlife values” (U.S. Fish and 

Wildlife Service 2012, p. 12). With this information from Tier 1 collected, developers will have important information about the sensitivity of the site within a larger 

landscape context, early in the development process. This information can help 

The primary 

management strategy 

to avoid or minimize 

the effects of habitat 

loss and direct 

collisions is to place 

wind energy facilities 

away from species of 

concern and areas of 

high wildlife value. 

The federal guidelines 

and those for Oregon 

and Washington all 

emphasize the best 

placement of wind 

turbines as the primary 

method to protect 

wildlife.
30

general technical report pnw-gtr-863

direct development away from locations that are associated with additional study 

need, greater mitigation requirements, and uncertainty. Alternatively, it can be 

used to identify the sensitive resources that will require further study if the site is 

to be developed “without significant adverse impacts to species of concern or local 

population(s)” (U.S. Fish and Wildlife Service 2012, p. 12). The guidelines note that 

some areas may be inappropriate for large-scale development because “they have 

been recognized according to scientifically credible information as having high 

wildlife value, based solely on their ecological rarity and intactness (e.g., Audubon 

Important Bird Areas, The Nature Conservancy portfolio sites, state wildlife action 

plan priority habitats)” (U.S. Fish and Wildlife Service 2012, p. 12). The USFWS 

guidelines include several suggested questions for developers under Tier 1:

1. Are there species of concern present on the proposed site(s), or is habitat 

(including designated critical habitat) present for these species? 

2. Does the landscape contain areas where development is precluded by 

law or areas designated as sensitive according to scientifically credible 

information? Examples of designated areas include, but are not limited 

to: federally-designated critical habitat; high-priority conservation areas 

for non-government organizations (NGOs); or other local, state, regional, 

federal, tribal, or international categorizations. 

3. Are there known critical areas of wildlife congregation, including, but 

not limited to: maternity roosts, hibernacula, staging areas, winter ranges, 

nesting sites, migration stopovers or corridors, leks, or other areas of 

seasonal importance? 

4. Are there large areas of intact habitat with the potential for fragmentation, with respect to species of habitat fragmentation concern needing large 

contiguous blocks of habitat? (U.S. Fish and Wildlife Service 2012, p. 13).

The guidelines then outline a decision process, so that if answers to all of the 

four questions above are “no” for one or more sites found within the area of investigation, the assessment indicates a low probability of significant adverse effects 

to wildlife. In this case, the developer would then proceed to Tier 2 investigation 

of the site characteristics. However, if any of these questions is answered “yes,” 

developers should proceed to Tier 2 to further assess the probability of significant 

adverse impacts to wildlife. Developers may consider abandoning the area or 

identifying ways in which project modifications will avoid or minimize potential 

significant adverse impacts (U.S. Fish and Wildlife Service 2012, p. 13). Within the 

Pacific Northwest, federal land management agencies are interested in conducting 
31

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

such a Tier 1 evaluation to guide prospective development. The BLM is conducting 

wildlife assessments for each state, examining areas where high-priority wildlife 

or habitats occur.6 The wider scientific literature reveals increasing interest in 

large-scale assessments of wind energy development impacts. For example, 

researchers used species-distribution and habitat suitability modeling to map 

predicted habitat quality for the lesser prairie-chicken (Tympanuchus pallidicinctus) 

throughout western Kansas (Jarnevich and Laubhan 2011). Researchers hope these 

relatively coarse-scale models can help guide energy development away from 

prime prarie-chicken habitat (Jarnevich and Laubhan 2011). Other regional-scale 

models have also incorporated wind potential, to balance tradeoffs between species 

protection and energy development (Eichhorn and Drechsler 2010). The USFWS 

maintains a list of risk assessment tools, which may also be used during site characterization (U.S. Fish and Wildlife Service 2011b).

Following the USFWS guidelines, once a specific site of interest is selected on 

a landscape, the Tier 2 process allows developers and managers to look at more sitespecific resources, and those that occur on smaller scales. During Tier 2, developers 

combine existing information with at least one site visit to complete their assessment. Questions posed to developers in the guidelines in Tier 2 are very similar the 

same questions posed in Tier 1, but are now applied to the site under consideration, 

with additional questions about plant communities, birds, and bats at the site (for 

more detail, see U.S. Fish and Wildlife Service 2012, p. 15). When completed, Tier 

2 site characterizations are expected to generally contain three components: (1) a 

review of existing information including published or available literature, databases 

and maps of topography, land use and land cover, potential wetlands, wildlife, 

habitat, and sensitive plant distributions; (2) information gathered from agencies 

and organizations that have relevant scientific information to further help identify if 

there are bird, bat, or other wildlife issues; and (3) one or more reconnaissance-level 

site visits to evaluate current vegetation/habitat coverage and land management/

use (to help determine the baseline against which potential effects from the project 

would be evaluated) (U.S. Fish and Wildlife Service 2012, p. 15). More detail on 

Tier 2 and specific resources for assessments, including a framework for evaluating 

habitat fragmentation, are in the USFWS guidelines (U.S. Fish and Wildlife Service 

2012, p. 15). Unless sufficient information is available to answer all Tier 2 questions 

and conclude either that a low probability of significant adverse impact to wildlife 

or that significant adverse impacts to species of concern cannot be adequately

6

 Buckner, G. 2010. Personal communication. Oregon state wildlife biologist, USDI Bureau 

of Land Management, 333 SW 1st Avenue, Portland, OR 97204.
32

general technical report pnw-gtr-863

mitigated, developers will proceed to Tier 3 to further consider potential impacts 

and mitigation.

Guidelines from BLM, Oregon, and Washington, and the Forest Service directives are all similar to USFWS guidelines in that they also recommend that developers avoid critical areas for wildlife, habitats of interest, or intact habitat. Forest 

Service guidelines list a number of siting considerations for species of management 

concern (defined as federally listed threatened and endangered species; species that 

are candidates for listing as threatened or endangered; Forest Service sensitive species, species of high public interest and state-protected species). For these species, 

directives advise potential project developers to:

1. Locate METs [meteorological towers], roads, turbines, and other necessary facilities away from protected areas or where ecological resources are 

known to be sensitive to human activities. Examples of these areas include 

wetlands, riparian zones, streams, lakes, bogs, or fens; globally unique, 

rare or threatened ecosystems; critical habitat of wildlife protected under 

Federal or State law; nests of hawks, eagle, falcons, and owls; and prairie or 

shrub-steppe grouse breeding grounds and habitat fragmentation.

2. Avoid or minimize the placement of towers and turbines in areas with a 

high incidence of frontal weather events that lead to frequent fog or mist if 

existing information indicates a high risk to migratory birds or bats during 

these weather events.

3. Avoid or minimize the placement of turbines in areas where topography 

and landscape features may funnel nocturnal migrants, such as over mountain passes, along river corridors, or ridge tops.

4. Use existing roads and utility corridors to the extent feasible, and 

minimize the number, length, and size of new roads, lay-down areas, and 

borrow areas.

5. Avoid placement of towers in habitat, security areas or critical range of 

species of management concern (USDA Forest Service 2011a, p. 11). 

More detailed guidance on avoiding or minimizing the potential for collisions 

and disturbance through siting is provided throughout the document (USDA Forest 

Service 2011a).

In both Oregon and Washington state guidelines, developers are advised to 

develop wind energy facilities on agricultural or disturbed lands, use existing 

transmission corridors and road networks, or place transmission corridors and other 

linear facilities in disturbed lands. Forest Service directives, BLM guidelines, and 
33

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

Washington state guidelines do not have an explicit staged or tiered process but 

do require preproject assessment to help design the project to avoid and minimize 

impacts to habitat and wildlife, followed by operational monitoring. Oregon state 

guidelines lead developers through five sequential phases, the first three of which 

deal with wind energy siting:

1. Macrositing to identify conflicts that may make a wind project prohibitively 

difficult to permit. 

2. Preproject assessment to identify wildlife and habitat resources on the 

potential wind project site and micrositing corridors that will be used to 

locate specific turbines and associated infrastructure.

3. Micrositing to determine the final wind project design (i.e., the final 

placement of turbines, roads, transmission lines, and other wind project 

features).

4. Construction where protective measures are used to avoid and minimize 

impacts to wildlife.

5. Operational monitoring determines the actual direct mortality impacts of 

the wind project on wildlife.

Preconstruction Wildlife Surveys

Because wind energy facilities are a relatively new land use, and much of their 

impact depends upon the combination of the site characteristics, wind energy 

facility characteristics, and needs and responses of wildlife populations, monitoring 

wildlife populations is key to determine and mitigate wind energy facility impacts. 

Therefore all guidelines contain recommendations for surveys, before a wind 

energy facility is built, to determine wildlife habitat and use and anticipate direct 

mortality impacts. 

Among existing guidelines, USFWS guidelines provide the most detailed 

recommendations about preconstruction survey methodology, intensity, and duration. Information on preconstruction wildlife monitoring is considered Tier 3 in the 

USFWS guidelines. Tier 3 recommends that developers study and further evaluate 

wildlife populations at a site in order to: “further evaluate a site for determining 

whether the wind energy project should be developed or abandoned; design and 

operate a site to avoid or minimize significant adverse impacts if a decision is made 

to develop; design compensatory mitigation measures if significant adverse habitat 

impacts cannot acceptably be avoided or minimized; determine duration and level 

of effort of postconstruction monitoring” (U.S. Fish and Wildlife Service 2012, p. 

19). Guidelines state that protocols for monitoring will differ with the species or 

ecological community studied, and with the site characteristics. Some species may 

Because wind energy 

facilities are a relatively 

new land use, and 

much of their impact 

depends upon the 

combination of the 

site characteristics, 

wind energy facility 

characteristics, and 

needs and responses 

of wildlife populations, 

monitoring wildlife 

populations is key to 

determine and mitigate 

wind energy facility 

impacts. 
34

general technical report pnw-gtr-863

have specific protocols required by local, state, or federal agencies. Because of the 

need for flexibility and the variation that may be encountered between projects, 

there are no specific recommendations on protocol in the USFWS guidelines. However, guidelines do recommend that preconstruction surveys be sufficient to answer 

the following questions about a wind energy facility’s potential impacts: 

1. Do field studies indicate that species of concern are present on or likely 

to use the proposed site? 

2. Do field studies indicate the potential for significant adverse impacts on 

the affected population of the species of habitat fragmentation concern?

3. What is the distribution, relative abundance, behavior, and site use of 

species of concern identified in Tiers 1 or 2, and to what extent do these 

factors expose these species to risk from the proposed wind energy project?

4. What are the potential risks of adverse impacts of the proposed wind 

energy project to individuals and local populations of species of concern 

or their habitats? (In the case of rare or endangered species, what are the 

possible impacts to such species and their habitats?)

5. How can developers mitigate identified significant adverse impacts?

6. Are there studies that should be initiated at this stage that would be continued in post-construction?” (U.S. Fish and Wildlife Service 2012, p. 20).

Comparing the efficacy of different survey techniques used in preconstruction monitoring is outside the scope of this document, but the USFWS guidelines 

provide more detailed information on monitoring and study for different species 

groups for each question above (U.S. Fish and Wildlife Service 2012). Guidelines 

also list additional references for methods and metrics tools in appendix C. As cited 

in the guidelines, Kunz et al. (2007a) discuss techniques for surveying nocturnal 

animals at length, and Strickland et al. (2011) overview methods and metrics for a 

range of taxa. U.S. Fish and Wildlife Service guidelines acknowledge the challenges 

of conducting surveys (often limited by cost), to support long-duration projects (30 

years of operations). To accurately characterize site use and conditions, they state 

that preconstruction studies may need to occur over multiple years. There are no 

specific recommendations for survey duration, but guidelines advise that survey 

duration be determined by conditions at each site:

“The level of risk and the question of data requirements will be based on 

site sensitivity, affected species, and the availability of data from other 
35

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

sources. Accordingly, decisions regarding the studies should consider information gathered during the previous tiers, variability within and between 

seasons, and years where variability is likely to substantially affect answers 

to the Tier 3 questions. These studies should also be designed to collect 

data during relevant breeding, feeding, sheltering, staging, or migration 

periods for each species being studied. Additionally, consideration for the 

frequency and intensity of preconstruction monitoring should be site-specific and determined through consultation with an expert authority based 

on their knowledge of the specific species, level of risk and other variables 

present at each individual site” (U.S. Fish and Wildlife Service 2012, p. 25).

Forest Service directives, and Oregon and Washington state guidelines all 

include recommendations for survey duration. Forest Service directives require a 

monitoring plan that describes all pre- and postconstruction monitoring in order to 

obtain a permit for construction and operation of a wind energy facility. Complete 

information on monitoring plans and techniques are provided in the Forest Service 

Handbook (USDA Forest Service 2011b). Preconstruction monitoring must be 

conducted for a minimum of 2 years, and be sufficient to capture interannual and 

interseasonal variability, and can be extended:

“Preconstruction monitoring should occur across multiple seasons in order 

to evaluate interseasonal variability in habitat use and to sample during 

migration periods of the target species. The sample size within each season 

should be sufficient to detect differences in presence, abundance, or activity level between seasons. The sample size should also be sufficient to meet 

the monitoring objective (has the wind energy facility resulted in changes 

in presence, abundance, or activity level) with a reasonable level of confidence” (USDA Forest Service 2011b, p. 8).

Directives provide more detailed guidance on the wildlife response to measure 

(wildlife presence, abundance, or activity level) (USDA Forest Service 2011b, p. 8). 

Forest Service directives also recommend that monitoring include those factors 

that potentially are changed by wind energy development, and impact wildlife 

populations, such as habitat quality or quantity, habitat fragmentation, noise, road 

density, and traffic volume (USDA Forest Service 2011b, p. 7). To accurately assess 

the effects of wind energy development, guidelines recommend the use of a beforeafter-control-impact study, which examines both a wind energy facility site and an 

ecologically similar nondeveloped site before and after a wind energy facility is 

established, to separate management impacts from other ecological impacts. Information from preconstruction monitoring can be used in an adaptive management 
36

general technical report pnw-gtr-863

framework to design wind energy facilities (turbine location and configuration) to 

reduce potential impacts to wildlife (USDA Forest Service 2011b). 

Oregon guidelines recommend 1 full year of raptor nest surveys and 1 year of 

avian use surveys, as well as bat surveys and surveys for threatened and endangered 

species and additional species of concern, if necessary. Survey durations may be 

reduced if there is preexisting relevant data, or expanded if managers expect high 

wildlife use of the wind energy facility site, if there is little background data, or if 

the project is especially large or complex. Washington’s guidelines recommend at a 

minimum 1 full year of avian use surveys, and one raptor nest survey. The surveys 

are to be taken during the breeding season within 1.6 km (1 mile) of the project 

to determine potential impacts of construction, with a larger survey area (e.g., a 

3.2-km [2-mile] buffer around project site) recommended if there is some likelihood 

of the occurrence of nesting state and federally threatened and endangered raptor 

species. Two or more years of relevant data are recommended if (1) risk to avian 

groups of concern is estimated to be high, (2) there is limited or no relevant data 

regarding seasonal use of the project site (e.g., data from nearby areas of similar 

habitat type), and (3) the project is significantly diverse in habitat and species. The 

BLM guidelines do not specify duration for preconstruction surveys.

Construction and Operation Practices

When the decision to proceed with a project has been made, there are a number of 

specific best management practices for the operation and design of the wind energy 

facility discussed in different guidelines, including factors such as lighting and 

vehicle operation (table 1). There are also some recent developments in the scientific 

literature that focus on how to best manage the time turbines are active. Although 

research has not yet yielded a recognized suite of best practices for managing 

turbine operation to reduce wildlife collisions, we summarize available information 

below. 

Strategies for modifying turbine operation may focus on particular times 

or weather conditions when wildlife is thought to be most active. For example, 

research indicates that bats are most active in the 2 hours after sunset and that their 

activity is closely tied to weather patterns and daily changes in insect abundance, so 

that stopping turbine operation during these periods would likely decrease fatalities 

(Horn et al. 2008). Another strategy focuses on changing the minimum windspeed 

at which turbines begin to turn and generate electricity (termed a “cut-in speed”) 

so that turbines remain idle at low windspeeds. This approach was successful in 

reducing bat mortality when tested in both Alberta, Canada and in the state of 

Pennsylvania in the United States (Arnett et al. 2011, Baerwald et al. 2009). In 
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Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

both instances, reductions in cut-in speed did not substantially reduce the amount 

of electricity generated because electricity is generated more efficiently at higher 

windspeeds, so that curtailing energy generation at lower speeds had a relatively 

small impact on total energy generated (Arnett et al. 2011, Baerwald et al. 2009). 

In addition, changes in cut-in speed occurred only at night when bats were active, 

allowing full energy production during the day. 

These experiments suggest that revising operational timing can be done with a 

high level of precision by working with facility managers to target specific turbines 

under certain conditions. For raptors, researchers have suggested stopping turbines 

at the top of slopes when the weather conditions indicate the highest risk of collision 

(e.g., when winds are strong and facing perpendicularly to the slope) (Smallwood 

et al. 2009). Researchers are also experimenting with real-time systems that use 

radar information on bat and bird presence to curtail turbines only when animals 

are present (U.S. Fish and Wildlife Service 2012, p. 47). Changing cut-in speeds, 

or otherwise modifying turbine activity with weather patterns or wildlife activity, 

will need to be further studied to determine this technique’s efficacy, but such 

targeted strategies are likely to be preferred over broader constrictions on operation. 

For example, a wind energy facility in West Virginia agreed to downscale a wind 

energy facility and stop operation completely during Indiana bat migration as part 

of a lawsuit settlement (turbines are operational only when bats are hibernating 

from mid-November to March 31) (Smith 2010). 

Postconstruction Monitoring

After a wind energy facility becomes operational, current guidelines call for 

monitoring so that wind energy facility operation and impacts on wildlife can be 

assessed over time, in an adaptive management framework. In the USFWS’s tiered 

system, postconstruction monitoring falls under Tier 4. Tier 4 includes monitoring 

both wildlife fatalities and other effects that result from project construction and 

operation. Guidelines recommend that postconstruction monitoring be designed to 

answer the following questions, related to fatalities and changes in habitat:

Fatality studies

1. “What are the bird and bat fatality rates for the project?” 

2. “What are the fatality rates of species of concern?” 

3. “How do the estimated fatality rates compare to the predicted fatality 

rates?” 

4. “Do bird and bat fatalities vary within the project site in relation to site 

characteristics?” 
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general technical report pnw-gtr-863

5. “How do the fatality rates compare to the fatality rates from existing projects in similar landscapes with similar species composition and use?” 

6. “What is the composition of fatalities in relation to migrating and resident 

birds and bats at the site?” 

7. “Do fatality data suggest the need for measures to reduce impacts?” (U.S. 

Fish and Wildlife Service 2012, p. 35).

Habitat loss, degradation, and fragmentation

1. How do postconstruction habitat quality and spatial configuration of the 

study area compare to predictions for species of concern identified in Tier 3 

studies?

2. Were any behavioral modifications or indirect impacts noted in regard to 

species of concern?

3. If significant adverse impacts were predicted for species of concern, and 

the project was altered to mitigate for adverse impacts, were those efforts 

successful?

4. If significant adverse impacts were predicted for species of concern, and 

the project was altered to mitigate for adverse impacts, were those efforts 

successful? (U.S. Fish and Wildlife Service 2012, p. 40).

Further information on postconstruction monitoring design and methods is 

included in the USFWS guidelines, including information on the duration and 

frequency of monitoring, number of turbines to monitor, delineation of carcass 

search plots, transects and habitat mapping, general search protocols, field bias and 

error assessment, and estimators of fatality (U.S. Fish and Wildlife Service 2012, 

p. 35–42). There are no fixed recommendations for postconstruction monitoring 

duration, but guidelines include survey decision-support matrixes that pair recommended duration and intensities of monitoring with perceived risk to wildlife identified in Tier 3, for both fatalities and habitat changes (U.S. Fish and Wildlife Service 

2012, p. 39, 42). 

Lastly, USFWS guidelines Tier 5: “Other postconstruction studies and 

research,” describes the settings where additional research may be needed. 

The USFWS anticipates that Tier 5 will not be necessary for most wind energy 

projects because the tiered approach would steer projects away from sites where 

this additional, potentially complex and time-consuming work would be required. 

Guidelines propose the following questions to determine if research is needed 

(i.e., answering “yes” to any of these questions might indicate that a Tier 5 study 

is needed):
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Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

1. “To the extent that the observed fatalities exceed anticipated fatalities, are 

those fatalities potentially having a significant adverse impact on local 

populations? Are observed direct and indirect impacts to habitat having a 

significant adverse impact on local populations?”

2. “Were mitigation measures implemented (other than fee in lieu) not effective? 

This includes habitat mitigation measures as well as measures undertaken 

to reduce collision fatalities.”

3. “Are the estimated impacts of the proposed project likely to lead to population declines in the species of concern (other than federally-listed species)?” 

(U.S. Fish and Wildlife Service 2012, p. 43).

More specific information about each of these questions and the circumstances 

in which Tier 5 studies may be conducted are provided in the USFWS guidelines, as 

well as some examples of Tier 5 studies.

Forest Service directives provide postconstruction monitoring guidance and 

require a minimum of 2 years of postconstruction monitoring, with an additional 

minimum of 1 year if any significant risks to species of management concern are 

identified (USDA Forest Service 2011b). An authorized officer can decide to require 

additional monitoring, based on the level of risk to species of management concern 

and the results of the first 2 years of monitoring. Directives state that long-term 

monitoring is essential to understanding the relationships between wildlife effects 

and the facility design and operation (USDA Forest Service 2011b, p. 9). More 

detailed information on postconstruction monitoring design and methods, including determining sample size, estimating mortality, monitoring tools, and evolving 

technology, is provided in Forest Service directives (USDA Forest Service 2011b). 

Information from postconstruction monitoring is intended to be used in an adaptive 

management framework, to refine operation of existing facilities, and guide development of future facilities (USDA Forest Service 2011b). Among state guidelines 

in the Pacific Northwest, Oregon provides specific guidance for survey duration (2 

years of bird and bat fatality monitoring, with adjustment as determined with the 

management agency), while Washington requires developers to work with managers 

to determine the duration and scope of the monitoring (Oregon Columbia Plateau 

Ecoregion Wind Energy Taskforce 2008, Washington Department of Fish and 

Wildlife 2009). The BLM guidelines do not specify duration for postconstruction 

monitoring but state that “monitoring program requirements, including adaptive 

management strategies, shall be established at the project level to ensure that 

potential adverse impacts of wind energy development are mitigated” (USDI 

BLM 2005b, p. A7).
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general technical report pnw-gtr-863

Future Research Needs for Minimizing Effects of Wind 

Energy Facilities on Wildlife

While there has been increasing scientific and management interest in understanding the impacts of wind energy on wildlife, many central questions about the relationship between wind energy facilities and wildlife populations remain unknown. 

Land managers require accurate information on the effects of wind energy facilities 

on wildlife, as supported by scientific studies, to formulate best management practices and manage wind energy developments. To further refine management and 

development of wind energy facilities, we draw from the research needs discussed 

in the scientific literature to synthesize priorities for future research. 

General Research Needs

• Long-term, before-after-control-impact studies are needed. In the scientific 

literature, there are repeated calls for longer term, scientifically robust studies before and after wind energy facility establishment to truly understand 

their impacts on wildlife species and to effectively compare different sites 

(Carrete et al. 2009, Cryan and Barclay 2009, Kunz et al. 2007b, Kuvlesky 

et al. 2007, Masden et al. 2009a, Stewart et al. 2007). Researchers prefer 

the use of which examine both a wind energy facility site and a nondeveloped site before and after a wind energy facility is established to separate 

management impacts from other ecological impacts (Kuvlesky et al. 2007). 

Such studies require careful matching of developed and control sites to 

relate results to the effects of wind energy development.

•	 Collaboration and data sharing with the wind energy industry could 

enhance research. Turbine facilities are uniquely suited for experimentation 

in their operations (turbine speed, activity, and placement), so that cooperation with industry could lead to significant gains in understanding how 

facility design and operation affects wildlife (Cryan and Barclay 2009). In 

addition, the industry has collected substantial site-specific information on 

wildlife populations before and after wind energy facility establishment, 

but such information is not always publicly available. As interest in wind 

energy development continues on public lands, data sharing could enhance 

federal land managers’ abilities to efficiently and accurately assess the 

potential effects of wind energy developments.

•	 Multisite studies will enhance scientific understanding. Studies involving 

multiple sites can provide more robust research results than studies carried 

out at one site, although larger studies take more time and resources (U.S. 

Fish and Wildlife Service 2012).
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Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

•	 Better methods to estimate population-level and cumulative impacts of 

wind energy facilities on wildlife. Understanding of behavioral responses 

or short-term effects of wind energy development are of limited use without 

expanded information on the population-level impact of habitat loss, disturbance, or mortality (Carrete et al. 2009, Masden et al. 2009a, Telleria 2009). 

Moving from a site-level impact to a population-level impact requires the 

ability to examine the cumulative impacts on wildlife populations, which 

will require information about species’ populations and ecology across their 

ranges as well as population models to simulate different scenarios of habitat loss and heightened mortality (Kuvlesky et al. 2007). As wind energy 

facilities proliferate, there has been increasing concern about their cumulative impact. However, there is no clear source of funding for this fundamental, population-level research because wind energy developers conduct 

assessments at smaller scales, focused on specific development sites.

•	 For bats, large-scale population surveys and more ecological studies are 

needed. Because there are no large-scale population estimates or surveys of bat species (Kunz et al. 2007b, Weller et al. 2009), it is difficult to 

understand how wind energy facility impacts at a site affect larger populations. Bat ecology and population dynamics are poorly known, but a better understanding of bat ecology, population dynamics, and migration is 

key to understanding the impacts of wind energy facilities on bats (fig. 4). 

However, as stated above, obtaining funding for this fundamental research 

may be challenging. 

Research Needs for Minimizing Habitat Loss or Modification

•	 How does wildlife respond to wind energy facilities, especially sage grouse 

and terrestrial mammals? There are limited studies of wildlife responses 

to wind energy facility developments, although previous studies on habitat 

loss and modification from road networks or other types of energy development may be helpful in predicting wildlife response to wind energy facilities. For sage grouse, the magnitude and proximal causes (e.g., noise, height 

of structures, movement, human activity, etc.) of those impacts on vital 

rates in grouse populations should be further studied (Becker et al. 2009). 

Information gained from such research should enhance our understanding of the buffer distances that are necessary to avoid or minimize adverse 

impacts of wind energy facilities on sage grouse. For both large and small 

mammals, there is little information on how species react to wind energy 

facilities and what kind of effects the loss and modification of habitat has 

on these species (Kuvlesky et al. 2007). 
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general technical report pnw-gtr-863

Figure 4—(a) A hoary bat roosting on the branch of a tree. (b) A hoary bat found dead 

beneath a wind turbine, an apparent victim of a blade strike or near-contact barotrauma. Paul Cryan, U.S. Geological Survey

Paul Cryan, U.S. Geological Survey

a

b
43

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

•	 How does turbine noise affect wildlife? Noise effects of wind energy facilities have mostly been studied in people, but past research on wildlife and 

noise suggests that wind turbines may affect wildlife. Topics of future 

research may include how wind facilities affect background sound levels; 

whether masking, disturbance, and acoustical fragmentation occur; and 

how turbine operation, construction, and maintenance sound levels can 

differ by topographic area (U.S. Fish and Wildlife Service 2012, p. 46). 

Experimental research that can isolate noise from other features of wind 

energy development (e.g,, examine the effects of turbine noise, visual disturbance caused by turbines, or traffic noise in isolation) will enhance our 

understanding of wind energy facility development and operation.

Research Needs for Minimizing Direct Mortality

•	 Better methods to predict the impact of wind turbines are needed. For 

both bats and birds, researchers would like to understand how weather, 

turbine design, and layout will relate to wildlife activity. Managers and 

researchers need better risk assessment models with appropriate confidence 

intervals on different scales to evaluate potential impacts of wind energy 

facilities. Refining efforts to predict collision risk and undertake regional 

assessments of wind energy facility impacts will help minimize impacts 

before facilities are constructed (Baisner et al. 2010). 

•	 Greater understanding of bat and bird migratory routes and behavior. 

If bat collisions occur more frequently where bat populations are congregated, researchers will need a greater understanding of migratory behavior. 

Monitoring thus far has suggested that migratory bat species are most often 

those struck or injured by turbines. With a greater understanding of migratory patterns, wind energy facilities might be able to avoid migration routes 

or curtail wind energy facilities during active migration (Cryan and Barclay 

2009). However, there is very little information on bat migratory patterns. 

Similarly, to better understand potential impacts of wind turbines on birds, 

researchers require better knowledge of migratory patterns and behavior for 

raptors and songbirds. Longer periods of pre and postconstruction monitoring will enhance our understanding of how bat activity and fatalities, in 

particular, relate to landscape conditions (topography, land cover) as well as 

weather conditions (e.g., windspeed, barometric pressure, air temperature), 

and the design of wind energy facilities (e.g., turbine size and height, the 

arrangement of turbines) (Arnett et al. 2008, Baldwind and Weller 2012, 

Kunz et al. 2007b). 
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•	 Develop and refine techniques for monitoring nocturnal bird and bat

behavior and activity. Studies of bat and bird behavior pose significant 

logistical challenges: turbines can be as tall as 40-story buildings, and 

migratory routes can span continents (Cryan and Barclay 2009). There are 

many different monitoring methods for nocturnal animals, including radar, 

thermal imaging, and acoustic monitoring. Refining these types of monitoring while combining them with physiological analysis of carcasses (e.g., 

using stable isotopes to determine migratory patterns or studies of reproductive status to examine demography) may yield valuable insights into 

patterns of wildlife mortality (Kunz et al. 2007a). 

•	 Better knowledge of raptor behavior in relation to wind turbines.

Raptors are species of conservation concern, and understanding how 

site-specific raptor behavior combines with wind turbine design, configuration, activity, and weather to produce mortalities would be valuable for 

managers.

•	 Behavioral research to examine why bats collide with turbines. At 

present, researchers largely do not know if bat collisions with turbines are 

occurring coincidentally (i.e., collisions are higher where there is more bat 

activity) or if bats are attracted to turbines, resulting in more collisions 

(Cryan and Barclay 2009). Researchers also require better data to understand exactly how bats are interacting with turbines, and under what circumstances (weather, site characteristics, turbine design) they are injured/

killed or escape injury (Horn et al. 2008). If bats are attracted to turbines, 

this preference would have significant implications for management, as 

managers might be able to minimize attractive features. Therefore, Cryan 

and Barclay (2009) recommended behavioral research to further examine 

this “attractive” turbine hypothesis as a top priority. 

•	 Further investigation into deterrents to decrease collisions. To reduce 

collisions, researchers and managers would like to develop deterrents to 

increase turbine avoidance. No one effective deterrent has emerged from 

research thus far, but a number of acoustic deterrents have been used in 

experiments (U.S. Fish and Wildlife Service 2012, p. 47).

Conclusion 

Both nationally and in the Pacific Northwest region (Oregon and Washington) there 

is growing public interest and policy pressure to develop wind energy facilities as 

a source of renewable energy. Wind energy facilities in the Pacific Northwest have 

expanded rapidly on private lands over the past decade, and there is now growing 
45

Synthesis of Wind Energy Development and Potential Impacts on Wildlife in the Pacific Northwest, Oregon and Washington

interest in development on federal lands. However, wind energy development has 

the potential to harm wildlife directly through collisions with wind turbines and 

transmission lines, as well as indirectly by modifying habitat. While information 

about the impacts of wind turbines on birds and bats has grown over the past 

decade, information on population-level effects over time as well as information 

on a wider range of species remains relatively unknown. Current federal and state 

guidelines acknowledge this uncertainty by emphasizing preconstruction studies, 

avoiding key wildlife habitat and species of concern when siting wind energy facilities, and conducting postconstruction monitoring of wind energy facility impacts. 

As wind energy development proceeds, augmenting this site-level research with 

basic research on key wildlife species’ migration, demography, and populations will 

be helpful in enhancing our ability to predict and understand population-level and 

cumulative impacts of wind energy facilities on wildlife.

Acknowledgments

This work was supported by the Station Director’s Office, Pacific Northwest 

Research Station. This report also served to fulfill the requirements, in part, of the 

Presidential Management Fellows Program for Miranda Mockrin. The document 

benefited from constructive reviews received from Ted Weller, Martin Raphael, and 

Dale Strickland. We also wish to thank Joyce Vandenbrook for her work creating a 

figure.

English Equivalents

When you know: Multiply by: To get:

Meters (m) 3.28 Feet

Kilometers (km) .621 Miles

Hectares 2.47 Square feet

Square meters (m2

) 10.76 Acres

Kilopascals (Kpa) .145038 Pounds per square inch
46

general technical report pnw-gtr-863

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