National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Bird Movements and Behaviors 

in the Gulf Coast Region: 

Relation to Potential Wind 

Energy Developments 

November 22, 2000 – October 31, 2005 

M.L. Morrison 

Department of Wildlife and Fisheries Sciences 

Texas A&M University 

College Station, Texas 

Subcontract Report 

NREL/SR-500-39572 

June 2006 
Bird Movements and Behaviors 

in the Gulf Coast Region: 

Relation to Potential Wind 

Energy Developments 

November 22, 2000 – October 31, 2005 

M.L. Morrison 

Department of Wildlife and Fisheries Sciences 

Texas A&M University 

College Station, Texas 

NREL Technical Monitor: Karin Sinclair 

Prepared under Subcontract No. TAT-1-31200-01 

Subcontract Report 

NREL/SR-500-39572 

June 2006 

National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
This publication was reproduced from the best available copy 

Submitted by the subcontractor and received no editorial review at NREL

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Table of Contents 

A. Introduction.................................................................................................................... 2 

1. Wind-energy status and proposed expansion.............................................................. 2 

2. Gulf Coast/Texas development................................................................................... 4 

B. Wind Potential in Gulf Coast/Texas............................................................................... 5 

C. Bird Movements and Behavior ...................................................................................... 7 

1. Bird migration along the Gulf Coast........................................................................... 7 

2. Potential environmental issues.................................................................................... 9 

3. Impacts on habitat and animal movements............................................................... 10 

4. Bird fatalities at land-based sites .............................................................................. 11 

a. Body of evidence from Europe ............................................................................. 12 

b. Turbine and wind farm characteristics.................................................................. 17 

c. Offshore oil platforms........................................................................................... 17 

5. Bat fatalities.............................................................................................................. 18 

D. Potential Bird-wind Interactions along the Gulf Coast................................................ 19 

1. Bird migration........................................................................................................... 19 

E. Proposal to Develop Risk Assessments........................................................................ 25 

1. Development of a strategic plan for wind development ........................................... 25 

2. Research and monitoring .......................................................................................... 26 

3. Initial site selection and permitting........................................................................... 26 

4. Sampling protocols................................................................................................... 27 

5. Risk reduction ........................................................................................................... 28 

a. Wind farm operation ............................................................................................. 28 

b. Turbine characteristics and location ..................................................................... 29 

c. Habitat management.............................................................................................. 30 

d. Turbine treatments................................................................................................ 31 

6. Research needs.......................................................................................................... 31 

F. Acknowledgments ........................................................................................................ 32 

G. Literature Cited ............................................................................................................ 33 
A. Introduction 

The United States has high-energy demands that are for the most part satisfied by the 

fossil fuel industries. Fossil fuel is a finite resource that will only become more valuable 

as supplies inevitably become more limited and as demand increases. Wind-generated 

energy may represent an alternative to fossil fuels for meeting electricity needs because 

harnessing wind energy does not generate the pollutants that burning fossil fuels 

produces. Furthermore, other than constructing the facility and supporting infrastructure, 

ecological communities are not disturbed to the same extent as occurs when coal deposits 

are extracted from the earth. 

Nevertheless, wind-energy facilities do impact natural resources. Although an individual 

wind turbine has a small footprint, wind farms consisting of dozens to hundreds or more 

turbines can cover hundreds to thousands of acres. The infrastructure required to install 

and maintain turbines in a wind farm can directly damage sensitive ecological 

communities through road building, clearing of tower pads, maintenance buildings, and 

electrical distribution lines. The presence of vehicles and personnel in wind farms may 

indirectly impact environmental resources through disturbance. So there is the risk of 

negatively impacting plant and animal communities associated with establishing 

financially viable wind farms. However, the primary concern associated with 

constructing wind farms may be the impacts that wind turbines might have on birds and 

bats. 

The purpose of this paper is to discuss the possible impacts of wind development to birds 

along the lower Gulf Coast, including both proposed near-shore and off-shore 

developments. I do this by summarizing wind resources in Texas, discussing the timing 

and magnitude of bird migration as it relates to wind development, reviewing research 

that has been conducted throughout the world on near- and off-shore developments, and 

providing recommendations for research that will help guide wind development that 

minimizes negative impacts to birds and other wildlife resources. 

1. Wind-energy status and proposed expansion 

Wind power has been used commercially to produce electricity since the early 1980s, 

when the world’s first large-scale wind development, or wind resource area (WRA), was 

developed in California. More than half of the United States has developed wind resource 

areas, and additional states are in various stages of the planning process. Wind 

developments are also prevalent throughout much of Europe, with most developments 

located relatively close to coastlines. Although the fatality rates in Europe are often 

higher than those in California and the rest of the United States, many European scientists 

have not considered this impact a significant threat to bird populations in most of Europe. 

This is because the number of deaths is small relative to the total number of birds using 

or passing through the area. Most birds killed were not raptors—they were relatively 

common species of passerines and waterbirds. Nevertheless, substantial kills of birds can 

take place if the turbines were placed in areas of relatively high bird use. Additionally, 

2
Europe has pioneered the installation of offshore wind developments, an application that 

is only beginning to be explored in North America. 

Researchers have conducted a large number of avian fatality surveys at WRAs in the 

United States and Europe. There has been an emphasis on raptor fatalities, despite the 

knowledge that other birds have been affected. This may be because raptors receive 

protection under a large suite of federal and state laws and because they are symbolic and 

have greater emotional value. For all avian species combined, estimates of the number of 

bird fatalities per turbine per year from individual studies have ranged from 0 at the 

Searsburg, Vermont and Algona, Iowa sites to 4.45 on the Buffalo Ridge, Minnesota 

Phase III site (Erickson et al. 2001). A study of golden eagle populations in the vicinity of 

the Altamont Pass (California) WRA from 1994 to 2000 reported that 52 of 257 eagles 

equipped with radio transmitters were killed by wind turbine strikes. When compared 

with other large WRAs, it is clear that Altamont Pass supports substantially higher 

resident and migratory raptor populations and experiences substantially greater raptor 

fatality rates caused by collision with wind turbines. (See Erickson et al. 2001 for a 

review). 

After examining the results of numerous bird impact studies at wind farms, Erickson et 

al. (2001) reported that the results are probably biased towards large birds because the 

carcasses of smaller birds are more difficult to detect and disappear more readily to 

scavengers. The results from most of the studies they reviewed indicated that more than 

50% of the bird mortalities detected were for raptors, while about 20% represented 

passerines. So the impact of wind farms on passerines may be more significant than the 

impact studies reveal. The primary available method for reducing the probability of avian 

collisions is locating wind farms in areas of relatively low bird utilization. Such pre-siting 

surveys are needed to appropriately locate wind farms and minimize the impacts to birds. 

Currently, utility-scale wind turbines can produce electricity for $0.04 per kilowatt-hour 

(kWh) on Class 6 wind sites (sites with average wind speeds of 6.7 meters (m) per second 

at 10-m height or16 miles per hour [mph] at 33 feet). However, as more sites are 

developed, easily accessible prime Class 6 sites are disappearing. In addition, many Class 

6 sites are in remote areas that do not have easy access to transmission lines. Class 4 wind 

sites (5.8 m per second at 10-m height or 13 mph at 33 feet) cover vast areas of the Great 

Plains from central and northern Texas to the Canadian border. Class 4 sites are also 

found along many coastal areas and along the shores of the Great Lakes. While the 

average distance of Class 6 sites from major load centers is 500 miles, Class 4 sites are 

significantly closer, with an average distance of 100 miles from load centers. Thus, utility 

access to the Class 4 sites is more attractive and less costly. Also, Class 4 sites represent 

almost 20 times the developable wind resource of Class 6 sites. Currently, wind energy at 

Class 4 sites can be marketed at prices in the range of $0.05 to $0.06/kWh 

(www.NREL.gov). 

3
2. Gulf Coast/Texas development 

Interest in establishing wind-generating facilities along the Lower Gulf Coast (LGC) of 

Texas has increased in recent years for several reasons. First, winds of sufficient 

magnitude to make a wind-generating facility economically viable occur at least part of 

every day along the Laguna Madre. Second, the terrain immediately inland consists of 

coastal prairie, so it is flat and has extensive open areas where wind turbines could be 

erected and operated on a daily basis. Third, electricity demands are evidently sufficient 

to operate a profitable enterprise. So the LGC appears to offer opportunities to provide 

competitive alternative energy sources to local consumers via wind-generating facilities. 

In 2005 the State of Texas began taking steps for permitting the first commercial offshore 

wind-energy development off of Galveston Island. Several wind energy companies have 

expressed an interest in Texas, in part because of the unique benefit the state offers in the 

competition to secure offshore wind development. In 1836, after securing independence 

from Mexico, Texas claimed the offshore boundaries observed under Spanish, then 

Mexican rule. Sam Houston, president of the new republic, successfully maintained 

sovereignty over all submerged lands in the Gulf out to 10.36 miles, or three marine 

leagues. Texas entered the Union in 1845 with its boundaries intact, and defeated an 

attempt at federal control of the tidelands in the 1950s. For this reason, the primary entity 

in Texas that an offshore wind developer must deal with is the Texas General Land 

Office. Also, development within the 10.36-mile limit offers proximity to the state's 

electrical grid to carry wind-generated power to customers. 

Texas Parks and Wildlife Department (TPWD) is the state agency that oversees fish and 

wildlife resources out to 10.36 miles offshore, including commercial and recreational 

fishing, and oyster and shrimp harvesting. TPWD provides recommendations on fish and 

wildlife resources to local, state, and federal agencies or private organizations that make 

decisions affecting those resources. 

Although wind turbine/bird collision studies seem to indicate that wind-generating 

facilities in some locations of the United States have a minor impact on birds compared 

to other sources of collision mortality, one cannot assume that similar impacts would 

occur among birds using wind-generating sites established on the LGC. Three migratory 

bird corridors converge immediately north of Corpus Christi, effectively funneling 

millions of birds along the LGC to wintering grounds in south Texas and Latin America. 

More than 200 species migrate along the lower Texas Gulf Coast annually, and several 

species on the federal threatened and endangered lists are included among these (e.g., 

golden-cheeked warbler [Dendroica chrysoparia] and black-capped vireo [Vireo 

atricapillus]). Moreover, a diverse and abundant resident bird community potentially 

composed of federally and state-listed threatened and endangered species will likely 

occur on any proposed LGC wind-generating facility site. 

Consequently, the impacts of a wind-generating facility located on the LGC could be 

different than those at different locations throughout the United States, simply because 

the abundance and diversity of birds that migrate or reside on any wind-generating 

facility site is so much greater. Moreover, the topography and vegetation communities of 

the proposed wind-generating sites in the LGC are very different from those of existing 

4
wind-generating projects, and these variables would likely influence the potential impacts 

of the proposed wind-generating facility on the bird community. Furthermore, storms that 

develop in or enter the Gulf of Mexico influence the movement patterns of migrating 

birds, generally forcing them toward the coasts. Inclement weather events also force 

migrating birds to lower altitudes, increasing the vulnerability of migrating birds to wind 

turbines. It will be very difficult to project the impacts of a wind-generating facility on 

LGC bird communities unless resident and migratory bird habitat use and movements are 

quantified prior to construction of such a facility. 

One company has recently obtained a long-term lease on a large private ranch with 

substantial Laguna Madre shoreline and has initiated the process of obtaining the federal 

and state permits necessary to begin construction of an 80- to100-turbine wind-generating 

facility. This company recognizes the potential impact that a wind-generating facility 

could have on resident and migratory birds that utilize the area encompassed by a windgenerating facility and is conducting an 8-month field evaluation to quantify the resident 

and migrant bird community, as well as identify important bird habitats on the proposed 

impact site. The company’s goal is to assess the risk of constructing a large windgenerating facility on the resident and breeding bird community on the impact site. 

B. Wind Potential in Gulf Coast/Texas 

The Panhandle contains the state's greatest expanse with high-quality winds. Wellexposed locations atop the caprock and hilltops experience particularly attractive wind 

speeds. South of Galveston, the Texas coast experiences consistent strong sea breezes 

that may prove suitable for commercial development. The mountain passes and ridgetops 

of the Trans-Pecos exhibit the highest average wind speeds in Texas. Since the wind in 

mountainous terrain can change abruptly over short distances, the best wind farm 

locations in West Texas are quite site specific. 

5
 

Figure 1. Potential wind production in Texas (1995 Texas Renewable Energy Assessment, 

Texas State Energy Conservation Office) 

The Texas map identifies three major areas with good wind power potential: the Great 

Plains, the Gulf Coast, and specific ridgetops and mountain passes throughout the TransPecos. The electric generation potential of the windy areas of Texas is summarized in 

Table 1, below. These values reflect exclusions for various technical and environmental 

constraints. The table points out that Texas contains enough class 4 resource to produce 

all of the electricity currently consumed in the state. Even when utilizing only class 5 and 

6 lands, wind power could generate a significant portion of the state's electricity. 

Table 1. Potential electricity production on windy lands in Texas 

WIND 

POWER 

CLASS 

AREA 

(km2

) 

PERCENT 

OF STATE 

LAND 

POTENTIAL 

CAPACITY 

(MW) 

POTENTIAL 

PRODUCTION 

(Billion kWh) 

% OF TEXAS 

ELECTRIC 

CONSUMPTION 

3 143,400 21.13% 396,000 860 371% 

4 29,700 4.38% 101,600 231 100% 

5 5,000 0.74% 21,600 48 21% 

6 300 0.04% 1,600 4 2% 

Total 178,400 26.29% 520,800 1,143 494% 

km2 = square kilometers

6
The potential of a location to produce energy from wind on a commercially viable scale 

is classified by “Wind Power Class,” which is based on averaged sustained wind speed: 

• Wind Power Class 1—very poor 

• Wind Power Class 2—poor 

• Wind Power Class 3—marginal (wind speed >14 mph) 

• Wind Power Class 4—good 

• Wind Power Class 5—very good 

• Wind Power Class 6—excellent (wind speed >18 mph) 

With the development of wind turbines that can operate at lower wind speeds, Wind 

Class 3 locations are now considered commercially viable. In fact, NREL is supporting 

research to develop wind turbines that would be economically viable in Class 3 wind 

regimes. 

C. Bird Movements and Behavior 

1. Bird migration along the Gulf Coast 

Radar studies have indicated that the flight pathway of the majority of trans-Gulf 

migrants in spring is directed toward the coasts of Louisiana and Texas (Gauthreaux 

1970, 1971, 1992), and thus over Gulf waters in which are located the majority of 

offshore oil and gas production facilities. Offshore platforms, which house production 

equipment and living quarters for personnel, have played a central role in the 

development of oil and gas resources in the Gulf of Mexico. The history of offshore 

platforms in the Gulf has been short but dynamic. The first offshore platform was 

installed in 1947. The first multi-platform complex was installed in 1960. By 1974, 800 

platforms had been installed in the Gulf. As the number of platforms grew, so did the 

geographic extent of their distribution offshore. Fixed platform installation depth reached 

30 m in 1955, 60 m in 1962, and 300 m in 1978. Production began in waters exceeding 

600 m in 1984, and in waters exceeding 1,500 m in 1997. The thousands of platforms 

now located on the continental shelf of the northern Gulf of Mexico make up the largest 

artificial island system in the world. 

One of the most important components of birds’ migration strategies is their use of local 

habitats for resting and refueling while en route. In light of the absence of natural islands 

or other terrestrial habitats during crossings of the Gulf of Mexico, it seems inevitable 

that the installation of thousands of artificial islands in the northern Gulf must affect 

migrants in some fashion. However, before 1998 few systematic studies had examined 

the influence of Gulf platforms on trans-Gulf migrating birds. From 1998 to 2000, 

Russell (2005) studied the ecology of trans-Gulf migration and the influence of platforms 

on migrants using a team of field biologists stationed on an array of platforms across the 

northern Gulf. 

In addition to the censuses of birds stopping over on the platforms, visual surveys of the 

airspace around platforms were used to assess the volume of flyby migration traffic and 

7
to quantify the flight behavior of trans-Gulf migrants. The researchers also compared 

their platform-based results to results of land-based radar (NEXRAD), including 10 radar 

sites that provide a nearly complete observational network around the northern Gulf 

Coast from Brownsville, Texas, to Key West, Florida. I summarize some of the findings 

of the Russell (2005) study below because of its importance in understanding specifics of 

bird migration along the lower Gulf Coast. (The Russell report presents a detailed 

presentation of data and should be reviewed for additional information.) 

Prior to this study, the conventional wisdom had been that spring trans-Gulf migration 

involves a roughly straight-line, shortest-distance flight from the Yucatan Peninsula to 

the upper Gulf Coast. Results of Russell (2005) support parts of this scenario but also 

indicate that the situation is considerably more complex. Backtracking from radar images 

and arrival times on platforms indicates that most spring migrants initiate their flights 

from the Yucatan Peninsula and/or the northern coast of the Isthmus of Tehuantepec. 

Radar and direct observational evidence indicate that most trans-Gulf migration takes 

place over the western Gulf and suggests that the migrants’ route is curvilinear and 

divergent, veering from a probable mean heading of northwest at points of origin, to 

north off the south Texas coast, to northeast off the Upper Texas Coast and Louisiana. 

Large flights are usually associated with Eastern Continental High (ECH) or Bermuda 

High (BH) synoptic weather patterns, in which winds similarly veer clockwise around the 

western Gulf. It appeared that the route of trans-Gulf migrants is influenced by the 

availability of tailwinds, with migrants attempting to minimize the time or energy 

expenditure required for crossing. This hypothesis is strengthened by the finding that 

centers of migrant offshore abundance as well as areas of eventual landfall varied in 

concert with synoptic weather. On ECH days when winds typically had a stronger 

westward component over the southern Gulf and often maintained a westward component 

over the northern Gulf, migrants were most abundant on platforms in the far western 

Gulf, and landfall was usually along the Texas coast. In contrast, on BH days, when 

winds had a weaker westerly component over the southern Gulf and usually an eastward 

component over the northern Gulf, peak offshore abundance shifted eastward and landfall 

was more likely to take place farther east along the northern Gulf Coast, occasionally as 

far as the Florida Panhandle. All available evidence indicates that the main migration 

stream is at least partially “steered” by synoptic-scale winds. 

Spring migration over the northern Gulf began between early morning and early 

afternoon, peaked 3 to 4 hours after first detection, and continued until 7 to 12 hours after 

first detection. Patterns of diel timing varied geographically and were related to weather, 

again consistent with a strong synoptic steering influence on migration routes across the 

Gulf. The bulk of spring trans-Gulf migration detected by radar occurred between March 

25 and May 24, but very large flights (>25 million migrants) occurred only in the 3-week 

period from April 22 to May 13. Waterfowl and herons peaked by early April. Shorebirds 

had widely varying migration schedules, with different species peaking as early as midMarch and as late as the end of May. Landbird migrants showed peaks throughout the 

season, but a majority of species peaked in the second half of April. Theoretical analyses 

of radar data yielded total seasonal estimates of 316 million trans-Gulf migrants in spring 

8
1998 and 147 million trans-Gulf migrants in spring 1999. Radar-observed spring 

migration was characterized by a series of pulses and tended to be “all-or-nothing”; that 

is, either significant trans-Gulf migration was evident on radar or else it was essentially 

absent. Dramatic hiatuses in radar-observed migration were always associated with 

strong cold fronts that penetrated deep into Mexico and set up persistent northerly winds 

over most of the Gulf. Conversely, radar-observed migration peaks were almost strictly 

associated with ECH and BH days. 

Fall trans-Gulf migration was more difficult to study because the extensive presence of 

aerial insects precluded quantitative interpretation of radar imagery. In addition, one of 

the two field seasons was partly compromised by prolonged absences from the platforms 

caused by tropical weather systems. Nevertheless, Russell (2005) thought that the 

heaviest trans-Gulf migration traffic in fall originates from the stretch of the northern 

Gulf Coast running eastward from Alabama. 

Southbound “fall” migrants were observed as early as May 20 and as late as January, but 

the vast majority of the migration occurred from mid-August to early November. There 

seemed to be several phases in the fall migration. During the early fall, migration by 

long-distance migrants appeared to be obligate (i.e., required) and was not strongly 

influenced by weather. Later in the fall, major trans-Gulf movements of shorter-distance 

migrants were generally associated with cold fronts and northerly winds. Direct 

observations at the eastern-most platform indicated that the direction of flight was most 

often due south but varied from south-southwest to south-southeast. As with spring, 

variation in the direction of travel was clearly influenced by wind. Russell and associates 

also detected considerable fall migration over the far western Gulf, where flight direction 

usually had a westerly component. The western-Gulf route was used by a high proportion 

of juveniles, and appeared to represent a risk-averse migration strategy favoring a shorter, 

less risky overwater flight leg at the expense of a more circuitous overall migration route. 

The researchers suspected that many of the adults traveling over the western Gulf were 

individuals that reached the northeastern Gulf Coast with inadequate fat stores for a direct 

trans-Gulf flight and worked their way westward along the coast, perhaps stopping over 

along the way. 

2. Potential environmental issues 

In specific situations, wind power developments have been shown to cause environmental 

impacts, including impacts on animal habitat and movements, noise pollution, visual 

impacts, biological concerns, bird/bat fatalities from collisions with rotating blades, and 

health concerns. Of all the potential environmental impacts, biological concerns 

regarding birds and bats have, to date, been discussed and studied the most. Various other 

issues associated with resource developments in general may also be of concern with 

wind developments; however, issues that are common to most if not all developments, 

such as soil erosion and water quality, are not addressed in this report. Morrison and 

Sinclair (2004) summarized many of the potential environmental concerns surrounding 

wind-energy development. 

 

9
3. Impacts on habitat and animal movements 

The term habitat refers to the specific configuration of environmental features (e.g., 

vegetation, rock outcrops, water) that an animal uses at any point in time. Habitat is a 

species-specific concept—every animal species uses a different combination of 

environmental features. Therefore, no specific area is “good” or “bad” habitat unless it is 

assessed in relation to a specific species. Thus, what is “good” for one species might be 

“poor” for another species. 

For wind developments, issues of habitat involve (1) outright loss because of 

development, (2) indirect impacts because of disturbance (i.e., the animal will no longer 

reside near the development), and (3) disruption in animal passage through or over the 

development because of the addition of towers and turbines. This definition also applies 

to offshore situations, and is applicable to foraging areas for birds, marine mammals, and 

fish. 

Because wind developments often stretch for many miles, the turbines, along with the 

associated infrastructure (especially roads), can impact animal movements. No 

quantitative work has been done on the impacts of wind developments on animal 

movements. It is unlikely, however, that onshore, inland wind developments will cause 

wholesale disruption in migratory movements of birds and other vertebrates. This is 

because wind developments are seldom, if ever, introduced into pristine environments. 

Migrating or dispersing animals do encounter a host of potential obstructions not 

necessarily associated with wind development, including highways, power line corridors, 

housing, farm fields and pastures, and people. Analysis of the impacts of a wind 

development on movements of terrestrial animals, therefore, would usually focus on the 

additional impacts that the wind development would have on animal movements. There 

are also numerous methods available to lessen potential impacts to animal movements 

that were developed for highways and other human developments, which could apply to 

wind developments. Such strategies would include widely spacing turbines in certain 

locations, restricting travel along roads within wind developments (e.g., for inspection 

and repair only) during specific times of year (e.g., during ungulate [i.e., large mammals 

such as deer] migration), and providing appropriate habitat between turbines to facilitate 

animal movements. 

The ground disturbance associated with placing a turbine, especially road cuts and cuts 

used for turbine pad placement, can actually attract certain species. Most notable are 

burrowing animals, such as gophers and ground squirrels. In some locations, these 

species are rare or legally protected. In most areas, the attraction of these animals to 

turbines likely enhances the area for foraging raptors, thus raising the likelihood of raptor 

collisions with rotating blades. As such, wind developments must consider the potential 

for attracting species of concern and creating conditions in which birds could be killed. 

At Altamont Pass, for example, research has shown that the abundance of rodent burrows 

is highest near turbine strings (Smallwood and Thelander 2005). 

A major concern with offshore developments is the impact that boat and air (helicopter) 

traffic to and from the wind development might have on animal behavior and movements. 

10
Here again, little is known about such impacts. The primary concern is that human 

activity in support of the development (e.g., supply delivery and maintenance crews) 

could have negative ramifications on animal behavior that extend far outside the 

boundaries of the turbines. Russell (2005) found that migrants would sometimes arrive at 

certain oil platforms shortly after nightfall and proceed to circle those platforms for 

variable periods ranging from minutes to hours. Circulations were highly variable in size 

and composition. The numbers of birds involved varied from a single individual to many 

hundreds. Although a wide variety of species was recorded in circulations, herons, 

shorebirds, swallows, and warblers were the dominant components. This behavior, if 

repeated around offshore wind turbines, could raise the risk of collision with the tower or 

the blade. Russell (2005) concluded that this circling behavior was related to attracting 

the birds to platform lights. 

Commercial turbines now commonly produce 1.5 to more than 2 megawatts (MW) of 

power, are three bladed, have a rotor-swept diameter of 70 m, and are placed on a tower 

80 m tall. Modern commercial wind turbines, therefore, have a maximum height 

measurement from ground level to the tip of the blade of 120 m (≈375’) or taller. Many 

offshore developments have proposed turbine-tower combinations that are near or exceed 

160 m (≈500’) in total height. As a result, turbines can be highly visible from many miles 

away. Larger turbines result in fewer turbines in an observer’s field of view, although the 

land area covered for a given wind farm megawatt capacity is approximately the same as 

for smaller turbines. In some locations, aircraft warning lights may be required by the 

Federal Aviation Administration (FAA), which adds another dimension to visual 

considerations. 

4. Bird fatalities at land-based sites 

Researchers have conducted a large number of avian fatality surveys at WRAs in the 

United States and Europe. In most cases, several factors have made it difficult to compare 

results from one study or one site to another. First, survey methods vary, and very few of 

these studies have been peer reviewed and published in scientific journals. Second, 

turbine designs and wind farm layouts vary considerably from site to site. Third, the wide 

climatic and topographical differences and range of bird species present in different 

locations make it extremely difficult to draw concrete conclusions from the available 

literature. Fourth, it is difficult to make statistical comparisons because the relatively low 

number of fatalities causes inadequate sample size. In addition, there was an initial focus 

on raptor fatalities, at least in part because raptors receive protection under a large suite 

of federal and state laws and because they are symbolic and have greater emotional value. 

Beginning in the late 1990s, increased work has been placed on evaluating the potential 

impacts to all bird species. A sampling bias toward raptors and other large birds also 

occurs because small birds are more difficult to detect and scavenging of small birds can 

be expected to occur more rapidly relative to larger birds. Impacts to some passerines, 

including neotropical migrants, may warrant more careful scrutiny because most of them 

are protected under the Federal Migratory Bird Treaty Act and because some are 

experiencing regional population declines. 

11
A study of golden eagle populations in the vicinity of the Altamont Pass WRA from 1994 

to 2000 reported that 52 of 257 eagles equipped with radio transmitters were killed by 

wind turbine strikes. When compared with other large WRAs, it is clear that the Altamont 

Pass supports substantially higher resident and migratory raptor populations and 

experiences substantially greater raptor fatality rates caused by collision with wind 

turbines. Although it remains inconclusive whether the eagle population in the Altamont 

region is declining due to turbine kills, these eagle fatalities may cause many direct and 

indirect impacts on the area’s bird population. Direct impacts include a decline in the 

population size and change in age structure. Indirect impacts include a reduction in the 

number of birds that are available to disperse to other regions. 

Results of numerous studies in the United States at sites outside of California have 

indicated that the rate of raptor collisions in California, particularly at the Altamont Pass 

WRA, is considerably higher than in other WRAs. Passerines composed the highest 

percentage of fatalities in the non-California studies. Reports from these studies indicate 

that the levels of fatalities are not considered significant enough to threaten local or 

regional population levels, although overall cumulative effects of human-induced bird 

fatalities are unknown. A major difference between the Altamont Pass WRA and other 

WRAs is that many other areas lack the dense populations of raptors and diverse 

topography of the Altamont Pass WRA and the large number of turbines sited. The high 

number of fatalities at the Altamont Pass WRA has created awareness of potential siting 

problems and, in some cases, more regard has been given to the level of raptor and other 

bird species use prior to construction. 

a. Body of evidence from Europe 

As reviewed below, offshore developments have been established throughout Europe, 

and there is now a body of evidence about potential ecological and human impacts from 

1-2 years of operation of the largest projects in Europe and about 280 studies of various 

types and scientific credibility. Most of these developments are small relative to onshore 

developments, although two larger projects are now operating in Denmark. 

There is a body of evidence in Europe regarding the potential environmental impacts 

from an offshore wind project because operating wind farms in the ocean have existed 

since the early 1990s. There are now over 280 studies relating to environmental and 

human effects research from offshore wind installations in Europe. There have been, 

however, concerns about the adequacy of this knowledge base as most of these projects 

had few turbines (less than 10), did not conduct rigorous BACI studies, and were not peer 

reviewed. In order to tackle this uncertainty and shape a credible story, the EU sponsored 

two major projects, Concerted Action for the Offshore Wind Energy in Europe (CAOWEE) and Concerted Action for the Deployment of Offshore Wind (COD). In 2005, 

COD compiled the available studies in a searchable electronic database and summarized 

their findings in a final report. “The COD work on the establishment of an environmental 

body of experience has brought an important overview of the present state of knowledge 

12
in this up to now unknown field” (COD 2005, 2).1

 Two Greenpeace International reports 

summarized environmental impact assessment studies in Europe prepared by Deutsches 

Windenergie Institute (2000) and Deutsche WindGuard GmbH (2005), respectively.2

 

 The major risks from offshore wind turbines to sea birds and resting birds are: 

• Permanent loss of habitat due to displacement; 

• Collisions with the turbines; and 

• Barrier effects, including fragmentation of the ecological habitat network (e.g., 

breeding or feeding areas). 

Of these, assessments suggest that collisions and disturbance have the main impacts on 

sea birds and resting birds (COD 2005, 23). Collisions of birds with wind turbines in 

offshore wind farms, in most cases, are only a minor problem (but with exceptions in 

some poorly-sited land-based facilities) (Greenpeace International 2000, section 5.3.3). 

Quantitative risks estimates for collision risks are difficult due to the facts that: 

• Impacts are highly site dependent; 

• Inadequate data exist on bird migration routes and flight behavior (Exo, Huppop, 

and Garthe, 2003, 50); 

• Impacts vary for different bird species; 

• Measurements address only found bird corpses; and 

• Results thus far are often contradictory between studies (Desholm and Kahlert 

2005). 

Still a number of studies thus far for offshore facilities suggest little or no impact on bird 

life (COD, 2001, 7-5). On the other hand, relatively high collision mortality rates have 

been recorded at poorly sited land-based wind farms in areas where a large concentration 

of birds are present, such as Altamont Pass and Tarifa (Birdlife International 2003). By 

contrast a recent study of 1.5 million migrating seabirds from Swedish wind farms in 

Kalmarsund concluded that the fatality risk to passing seabirds was only one in 100,000 

passing seabirds (Eriksson and Petersson 2005). 

In Denmark, radar studies have shown that migrating birds avoid flying through the 

Nysted wind farm. These studies reveal that 35 percent of the birds fly through the area at 

baseline, but only 9 percent after construction. Monitoring at the operating Horns Rev 

wind farm in Denmark found that, “...most bird species generally exhibit an avoidance 

reduction to the wind turbines, which reduces the probability of collisions (Elsam 

Engineering and ENERGI E2, 2005, 45). 

 

1

 See the CA-OWEE and COD reports and database at www.offshorewindenergy.org. See the summary in 

“COD, Principal Findings 2003-2005, prepared by SenterNovem in the Netherlands, as part of a series 

highlighting the potential for innovative non-nuclear energy technologies. 

2

 See “Offshore Wind: Implementing a New Powerhouse for Europe; Grid Connection, Environmental 

Impact, Assessment, Political Framework,” 4 April 2005, WindGuard GmbH Commissioned by 

Greenpeace, at http://www.greenpeace.org/international/press/reports/offshore-wind-implementing-a and 

“North Sea Offshore Wind—A Powerhouse for Europe; Technical Possibilities and Ecological 

Consideration”, 2000. 

13
Thus far, the risks of habitat loss and barrier effects for birds have not been quantitatively 

estimated. The avoidance behavior of birds is significant in these risks. Such avoidance 

behavior is species-specific and the overall availability of suitable areas is important. 

Large offshore wind farms may diminish foraging and resting conditions and so 

assessment of cumulative effects is needed. Sea birds and resting birds appear to be less 

at risk than migrating birds (COD 2005, 32), as they may adapt better to offshore wind 

farms. 

Despite the lack of evidence to suggest a major overall risk to birds, this issue remains 

high in public concern and in European priorities. It is important to note that while further 

studies are needed to better define the risks, precautionary measures to reduce and 

mitigate such risks exist. For example, careful siting of wind farms away from bird 

migratory paths, bird habitats, and large concentrations of species at higher risk is 

possible. 

From preliminary Danish monitoring results, it appears that offshore wind farm-induced 

effects are less severe than might have been anticipated. However, knowledge gaps and 

uncertainties on cumulative effects from other sea users suggests that further work and, in 

the meantime, careful assessment and monitoring, is merited. As to the impact on fish, it 

appears that no significant adverse effects from the building and operation of wind 

turbines has been demonstrated. It is generally believed that wind farm areas may have 

positive impacts as these may serve as a refugium for fish. There appears to be no 

common expert opinion on how offshore wind farms effects benthos communities 

(especially the long-term impact on composition of benthic species and communities). 

Most of the European studies focused on solitary or small groups of turbines. Therefore, 

it is difficult to compare data with U.S. studies that focus on larger groups of turbines. 

Many of the European studies were based on coastal sites where waterfowl and migratory 

bird issues were not comparable to those in the California studies. Although the fatality 

rates in Europe are often higher than those in California and the rest of the United States, 

many European scientists have not considered this impact a significant threat to bird 

populations in most of Europe because the number of deaths is small relative to the total 

number of birds using or passing through the area. Most birds killed were not raptors—

they were relatively common species of passerines and waterbirds. 

A summary of bird-wind interactions in Europe found that overall kill rate was low. It 

was noted, however, that 2 to 3% of birds passing a windfarm at rotor height were killed. 

It has been concluded that disturbance and habitat loss effects associated with wind 

developments were probably much more important than direct bird kills due to collisions. 

In Spain, however, relatively high levels of kills were sometimes evident. Research in 

Europe has indicated that individual and single rows of turbines in areas with small bird 

populations provide the best landscape for wind farms (e.g., Winkelman 1995). 

J. Winkelman conducted a series of studies examining the impacts of on-land but nearshore wind developments on birds; several of these studies are reviewed below. 

Winkelman (1994) provides an overview of research carried out in Europe with special 

14
emphasis on the results of the two most in-depth studies (Winkelman 1992 parts 1-4). 

Winkelman provides data and tables that are not available in any of the English 

summaries of these reports. Up to 1994, 14 studies have been finalized in Europe, 

covering 108 different sites. Most studies include small, solitary turbines (100 to 150 

kW). Studies on bird collisions were mostly carried out by searching for dead birds. The 

proportion of birds colliding in relation to the total number passing the wind turbines was 

studied at 13 sites. Estimates of the total number of bird deaths could only be made in 

two studies. At the 108 sites, 303 dead birds were found, of which at least 41% were 

proven collision deaths. Of 14 collisions visually observed, 43% were caused by birds 

swept down by the wake behind a rotor, 36% by a rotor, and 21% unknown. The author 

states that total numbers likely to be killed per 1,000 MW of wind power capacity are low 

relative to other human-related causes of death. Findings on disturbance and the effect of 

turbines on flight behavior, which were investigated in most studies, were summarized. 

Up to a 95% reduction in bird numbers has been shown to occur in the disturbance zones 

(250 to 500 m from the nearest turbines). From the European point of view, in most 

circumstances disturbance and habitat loss is thought to be of much more importance 

than bird mortality. New or ongoing research in Spain, The Netherlands, and Denmark 

was also mentioned. 

Winkelman (1992) presents the first of a four-part series of reports showing the results of 

a continuing study to determine the impact of an experimental wind park on birds and 

reports results of searches for birds that died or were injured by collision with turbines 

and meteorological towers from 1986 to 1991. Seventy-six injured or dead birds were 

found, representing 25 species. Of these, 36% were certainly or very probably killed as a 

result of collision with turbines, while 17% were injured. Fewer birds probably collided 

with the middle row of wind turbines. Consequently, Winkelman suggests that a cluster 

formation of turbines may cause fewer impacts than a line formation. All birds that were 

thought to be killed by turbines were found in the area behind the rotor or on the right 

front side of it. Most deaths were found after nights with both poor flight and sight 

conditions. On average, less than 0.01% of the birds passing the wind park during 

nocturnal or diurnal migration collided with an obstacle in the wind park. Lighting of 

wind turbines is believed to be harmful rather than beneficial, particularly when weather 

and visibility are bad. 

Winkelman (1985) studied the possible danger to birds of medium-sized wind turbines 

(tower height 10to30 m) situated on six small windfarms located along or near the Dutch 

coast. The main points addressed by the study were the flight behavior of birds 

approaching turbines in daylight, the number of birds killed at night, and the possible loss 

of breeding and feeding habitat around turbine sites. Diurnal migrants seemed to respond 

more to operating turbines than local birds. An average of 13% of migrating flocks and 

5% of local flights showed a change in flight behavior that could be attributed to the 

turbines. The results suggest that local birds habituate to wind turbines. Within 12 species 

groups during diurnal migration, the greatest response to operating turbines was shown in 

ducks and geese. Of the diurnal migrants, 3% of the flocks came within reach of the rotor 

and 1% showed a panic reaction. At present sites, the disturbing effect of turbines on 

breeding and feeding habitat of birds has been negligible. No collisions with turbines 

15
were recorded. However, there were no data on carcass removal by scavengers and sites 

are situated in areas of low bird life. The study concluded that the chance of collisions of 

birds with medium-sized turbines in daylight and in weather with good visibility is 

almost zero. The author advised caution that the study does not indicate the danger of 

collisions at night or in poor visibility, by large groups of turbines, and by turbines at 

sites in the open field. 

Winkelman (1990) deals with the behavior of birds approaching wind turbines during day 

and night conditions. Specific questions include how many birds pass the turbines at 

tower height and what proportion of these birds have collided with the turbines. 

Specialized equipment (search approach radar, passive image intensifiers in combination 

with infrared lights, and thermal image intensifiers) was used to determine abundance, 

behavior, and height of birds flying at night or during poor visibility. Ninety-two percent 

of birds approached the rotor without any hesitation during the day compared to 43% 

during the night. Most of them did approached the rotor with strong wing beats or a 

fluttering flight, particularly when there were head winds compared to tail winds. During 

high-use nights, 56 to70% of the birds passed at rotor height (21 to 50 m). More birds 

collided with the rotor at night and twilight than during the day. Of 51 birds recorded 

trying to cross the rotor area during twilight and total darkness, fourteen (28%) collided. 

During daylight, only one of fourteen birds (7%) collided. Bird accidents were not always 

real collisions. In 43% (6 of 14) of the nocturnal accidents observed, the birds were swept 

down through the wake behind the moving rotors during tailwinds. Half of these birds 

recovered soon after these collisions. The report also compares flight heights of birds 

during day and night conditions. Based on the number of birds passing at rotor height and 

the proportion of birds colliding, an estimated 1 out of 76 birds passing the towers at 

night was expected to collide mortally with the turbines when the park was fully 

operational. 

Exo et al. (2003) reviewed the status of offshore wind-energy developments and research 

on birds in Europe. They noted that European seas are internationally important for a 

number of breeding and resting seabird populations that are subject to special protection 

status. Moreover, every year tens of millions of birds cross the North Sea and the Baltic 

Sea on migration. The erection of offshore wind turbines may affect birds as follows: (1) 

risk of collision; (2) short-term habitat loss during construction; (3) long-term habitat loss 

due to disturbance by turbines, including disturbances from boating activities in 

connection with maintenance; (4) formation of barriers on migration routes; and (5) 

disconnection of ecological units, such as between roosting and feeding sites. These 

researchers also stated it was vital that all potential construction sites are considered as 

part of an integral assessment framework, so that cumulative effects can be fully taken 

into account. They concluded, however, that making these assessments was hindered by a 

lack of good data on migration routes and flight behavior of many of the relevant bird 

species. They added that, based on experience gained from studies at inland wind 

facilities and at the near-shore sites where environmental impact assessments are 

currently underway, marine wind farms could have a significant adverse effect on 

resident seabirds and other coastal birds as well as migrants. Moreover, the potential 

16
impacts may be considerably higher offshore than onshore. Disturbance and barrier 

effects probably constitute the highest conflict potential (Exo et al. 2003). 

b. Turbine and wind farm characteristics 

Various design features, such as perch availability, rotor diameter, rotor-swept area, rotor 

height, rotational and tip speeds, and fixed versus variable turbine speed have been 

evaluated to determine whether they contribute to bird collision risk. Although at one 

time workers suggested that lattice towers might encourage birds to perch and thus come 

into close proximity of rotating blades, recent studies have failed to confirm a correlation 

between tower type and fatality rates. 

The issue of rotor-swept-area and blade-diameter effects on avian collision risk with 

turbines is important because wind developers are in the process of repowering or 

replacing existing, less efficient turbines with a smaller number of new, larger, and more 

efficient turbines. Existing studies concerning fatalities in relationship to increased rotorswept area are inconclusive, and further research is needed. 

It has been speculated that overall bird fatalities will be higher at taller turbines because 

of an increased potential for collisions by neotropical migrant species. It is well known 

that migrating songbirds are frequently killed at tall communication towers. This was 

attributed to higher-flying, non-raptor nocturnal migrants that often constitute the greatest 

percentage of fatalities. Behavior differences among raptors indicate that there may be 

some trade-offs in benefits. For example, one species may benefit from blade tips being 

further from ground level, whereas others may be exposed to greater risk from blades that 

reach a greater overall height. Further research is needed to determine the impact that the 

newer, taller turbine towers have on bird kills. Rotor velocity and a corresponding 

increased tip speed have been correlated with fatalities. Faster turbine rotor speeds kill 

more raptors than would be expected by chance. 

c. Offshore oil platforms 

Russell (2005) documented a total of 787 cases of migrant mortality on or near oil 

platforms during the three spring seasons of study. Starvation was the most common 

cause of death (46% of deaths in which a cause was assignable), followed by collision 

(34%), and predation (14%). Among the total of 780 cases of migrant mortality 

documented on or near platforms during the two fall seasons of study, collision was the 

most common cause of death, accounting for 48% of deaths in which a cause was 

assignable. Predation was relatively more common in the fall (36% of deaths, compared 

to 14% in spring). However, starvation was uncommon in the fall, with only 76 

documented cases in the 2 years. Collision deaths revealed that most occurred very early 

in the morning with strong winds from the south, when the vanguard of northbound 

migrants actually reached platforms before the onset of daylight. In contrast to spring, 

starvation was relatively rare and collision was the most common cause of death in the 

fall. Starvation was rare in part because the platforms are much closer to points of 

departure in the fall (i.e., migrants arriving on platforms have had less time to deplete 

17
their fat stores). Collision mortality is more significant in the fall because most migrants 

in that season are aloft over the northern Gulf during hours of darkness. Based on the 

seasons with heaviest observed collision mortality (spring 1998, fall 1999), Russell 

(2005) concluded that an average Gulf platform may cause 50 deaths by collision per 

year, suggesting that the platform archipelago may cause roughly 200,000 deaths per 

year. This number may be biased low because some birds that collide with platforms 

undoubtedly fall into the sea and avoid detection. 

5. Bat fatalities 

Until recently, little research has been conducted to determine the impacts of wind farms 

on bats. A few bat carcasses were found during earlier bird fatality studies; however, 

recent surveys at some newer sites have discovered higher mortalities than reported 

previously. To better discern the level of collision impacts on bats, researchers have 

initiated studies at some of these sites. These studies include analysis of environmental 

features in and around wind farms that could attract bats, such as roosting sites, 

availability of surface water, and riparian foraging areas. 

Erickson et al. (2002) included a summary of bat fatalities at wind farms. The researchers 

found that some bat mortality can be expected at most wind plants, with a very large 

majority of the fatalities involving migratory tree and foliage roosting bats such as hoary 

and silver-haired bats in the western United States, and hoary and eastern red bats in the 

Midwest and eastern parts of the country. Bat collision mortality during the breeding 

season is virtually nonexistent, despite the fact that relatively large populations of some 

bat species have been documented in close proximity to wind plants. These data suggest 

that wind plants do not currently impact resident breeding bat populations in the United 

States. All available evidence indicates that most of the bat mortality at U.S. wind plants 

involves migrant or dispersing bats in the late summer and fall. 

Bat echolocation and collision mortality studies indicate that only a small fraction of 

detected bat passes near turbines result in collisions, and that there appears to be little 

relationship between bat activity at turbines and subsequent collision mortality (Erickson 

et al. 2002). This relationship may not exist because many of the migrant species 

involved may either not be echolocating, or they are flying too high for the bat detectors 

to record, but still may be within the zone of collision risk. One of the largest estimates of 

bat fatalities is from the wind plant at Buffalo Ridge, Minnesota. Preliminary data from 

this site collected during a 5-year study suggest that the number of bats susceptible to 

turbine collisions is large, but the observed mortality is not sufficient to cause population 

declines of potentially affected bat species, based on relatively stable fatality rates over 

time. However, the effect on migrant populations of sustained collision mortality over 

several years is not known. 

Arnett (2005) studied the relationships between bats and wind turbines at the 

Mountaineer Wind Energy Center in West Virginia, and at the Meyersdale Wind Energy 

Center in Pennsylvania. Fatality searches located a total of six species at Mountaineer and 

seven at Meyersdale during the 6-week sampling period: hoary bats, eastern red bats, 

18
eastern pipistrelles, little brown bats, silver-haired bats, big brown bats, and northern 

long-eared bats (only found at Meyersdale). Fatalities were distributed across all turbines, 

although higher-than-average numbers of bats generally were found at turbines located 

near an end or center of the string at both sites. Of the 64 turbines studied, one was 

nonoperational throughout the study period and this was the only turbine where no 

fatalities were found. Bat fatalities were not different between turbines equipped with 

FAA lights and those that were unlit at both sites. The majority of bats were killed on low 

wind nights when power production appeared insubstantial, but turbine blades were still 

moving, often times at or close to full operational speed. Fatalities tended to increase just 

before and after the passage of storm fronts. Daily searches at Mountaineer yielded an 

estimated 38 bats killed per turbine and a daily kill rate of 0.90 bats per turbine. The total 

number of bats estimated to have been killed by the 44 turbines just during this 6-week 

period was 1,364 to 1,980. At Meyersdale, an estimated 25 bats were killed per turbine 

based on daily searches, yielding a daily kill rate of 0.60 and a total of 400 to 660 bats 

killed by the 20 turbines during the 6-week study. 

D. Potential Bird-wind Interactions along the Gulf Coast 

1. Bird migration 

Texas in general is considered part of the Central Flyway. The Central Flyway merges 

toward the east with the Mississippi Flyway and is bounded to the east by the Missouri 

River. The Central Flyway runs through western Missouri, Arkansas, and Louisiana, and 

then follows the Gulf coast of Mexico southward (Figure 2). 

 

19
Figure 2. The primary routes taken by migratory birds through Texas and the lower Gulf 

Coast. Illustrator: J. Pahountis-Opacic 

When landbirds start their southward migration, there is a convergence of the lines of 

flight taken by individual birds because of the conformation of the land mass and the 

east-west restriction of habitats suitable to certain species (Lincoln et al. 1998). For 

example, the Rose-breasted Grosbeak leaves the United States through the 600-mile 

stretch from eastern Texas to Apalachicola Bay, but thereafter it crosses the Gulf of 

Mexico and enters the northern part of its winter quarters in southern Mexico (Figure 3). 

A narrowing of migratory paths is the rule for the majority of North American birds. Both 

the shape of the continent and major habitat belts tend to constrict southward movement 

so that the width of the migration route in the latitude of the Gulf of Mexico is much less 

than in the breeding range. The American Redstart represents a case of a wide migration 

route, but even in the southern United States this path is still much narrower than the 

breeding range (Figure 4). 

20
Figure 3. Distribution and migration of the Rose-breasted 

Grosbeak. Though the width of the breeding range is 

about 2,500 miles, the migratory lines converge until the 

boundaries are only about 1,000 miles apart when the 

birds leave the United States (Lincoln et al. 1998). 

21
Figure 4. Distribution and migration of the Redstart. An 

example of a wide migration route, birds of this species 

cross all parts of the Gulf of Mexico, or may travel from 

Florida to Cuba and through the Bahamas. Their route has 

an east-and-west width of more than 2,000 miles (Lincoln 

et al. 1998). 

The largest number of migrating birds cross the Gulf of Mexico from the northern Texas 

coast, eastward to the Florida panhandle (Figure 5, route 4). As evident from Figure 5, 

crossing the Gulf represents the shortest route to extreme southeast Mexico. In contrast, 

birds migrating along the LGC tend to follow the coastline because of its primary north22
south orientation, rendering crossing the Gulf relatively less important (Figure 5, route 5) 

(Lincoln et al. 1998). 

Figure 5. Primary migratory routes of birds (Lincoln et al. 1998) 

Sidney A. Gauthreaux, Jr. (Department of Biological Sciences, Clemson University, 

Clemson, South Carolina) has pioneered the use of weather surveillance radar to monitor 

bird migrations. Doppler weather surveillance radar (WSR-88D) on the Gulf coast 

provides information on the direction and speed of bird movements⎯all displayed in 

bright colorful images. When properly calibrated, the WSR-88D can be used to measure 

the density of migrating birds aloft and use the speed of movement relative to the winds 

aloft to roughly determine the types of birds involved. Based on simultaneous visual 

observations, it was found that small songbirds flew considerably slower than shorebirds 

and waterfowl. This information revealed that flight contains not only flocks of 

songbirds, but also flocks of herons, waterfowl, shorebirds, gallinules and allies, and 

occasionally raptors. By simultaneously monitoring all the WSR-88D radars along the 

northern Gulf coast, the researchers were also able to determine the spatial extent of 

trans-Gulf flights. While migrants could be detected arriving from Brownsville, Texas, to 

Mobile, Alabama, the Houston and Lake Charles radar stations recorded more arrivals 

than any other station on the northern Gulf coast. 

The Gauthreaux research program has shown that migrant birds take off 30 to 45 minutes 

after dark—an exodus event—and climb into the early evening sky. As they climb to 

altitudes sampled by the radar beam, they become "visible" as echoes in the radar image. 

For a brief period of time the locations of echoes from concentrations of migrants 

indicate the geographical locations of the stopover areas. The strength of the cluster of 

23
echoes indicates the density of birds and may indirectly indicate the quality of the habitat 

at the associated stopover area. Once images showing exodus events are summed over a 

season and imported as a data layer into a geographic information system, remote sensing 

imagery can be used to determine the topography and type of habitat in stopover areas. 

These maps show the density and direction of peak migratory movements over the radar 

stations, and in time will allow one to determine if migratory flights are decreasing, 

stable, or increasing for different regions of the country. With this initiative in place they 

can monitor the status of migration systems along the Gulf coast (and throughout the 

United States). 

The most direct route for many Neotropical and Nearctic migrants wintering in the 

Caribbean and Central and South America to breeding grounds in eastern and central 

North America is across the Gulf of Mexico. Birds must cross this ecological barrier in a 

single flight, often choosing to fly when weather conditions are most favorable for this 

long journey. Birds leave Yucatan, Central America, and Caribbean islands 30 to 45 

minutes after sunset, and they fly through the night. The distance from these departure 

sites to the U.S. Gulf coast is 400 to 600 miles; under favorable weather conditions and 

depending on the species (and thus flight speed) birds arrive from just before dawn to the 

late morning or early afternoon. If birds encounter unfavorable weather conditions, such 

as those associated with a frontal passage, their arrival can be delayed by many hours. 

Migrating birds do not fly well through heavy precipitation and will often be forced to 

land if a storm is strong enough. If the birds can detect the storm by sight, smell, sound, 

humidity, or pressure, they may fly around or away from it (summarized from 

S. Gauthreaux). 

A substantial number of raptors migrate through the LGC during fall. For example, the 

Hazel Bazemore Hawk Watch is conducted annually near Corpus Christi (Nueces 

County). The count of raptors for the 2004 season totaled 1,030,762 birds as follows by 

species: 

 1,016 Black vulture 

 17,750 Turkey vulture 

 205 Osprey 

 34 Swallow-tailed kite 

 2 White-tailed kite 

 4,440 Mississippi kite 

 3 Bald eagle 

 101 Northern harrier 

 895 Sharp-shinned hawk 

 480 Cooper's hawk 

 24 Red-shouldered hawk 

989,875 Broad-winged hawk 

 14,753 Swainson's hawk 

 178 Red-tailed hawk 

 2 Ferruginous hawk 

 19 White-tailed hawk 

24
 1 Short-tailed hawk 

 2 Zone-tailed hawk 

 23 Harris's hawk 

 1 Golden eagle 

 365 American kestrel 

 32 Merlin 

 143 Peregrine falcon 

 2 Prairie falcon 

 4 Crested caracara 

 252 Unknown accipiters 

 48 Unknown buteos 

 15 Unknown falcons 

 88 Unknown raptors 

 9 Unknown vultures 

Note that nearly 1 million broad-winged hawks were observed, along with more than 

17,000 turkey vultures; 14,000 Swainson’s hawks; and 4,000 Mississippi kites. The 

movement of raptors from areas to the north and then south into and along the Gulf Coast 

occurs along a broad front. Thus, there are millions of raptors moving through the Gulf 

Coast during fall (August through November). 

Endangered and threatened species found in Texas include the peregrine falcon, bald 

eagle, black-capped vireo, eastern brown pelican, golden-cheeked warbler, interior least 

tern, piping plover, whooping crane, Mexican long-nosed bat, Rafineaque’s big-eared 

bat, southern yellow bat, and spotted bat. Note that the whooping crane winters in an area 

centered at Aransas National Wildlife Refuge, which is located centrally along the LGC. 

E. Proposal to Develop Risk Assessments 

1. Development of a strategic plan for wind development 

The United Kingdom has completed a Strategic Environmental Assessment (SEA) for 

wind-energy development, a process that is similar to the Environmental Impact 

Assessment process in the United States. Also, other European counties have strategic 

plans in motion. For example, the potential for substantial offshore development of wind 

resources led the United Kingdom to develop a comprehensive strategy for siting wind 

farms. The United Kingdom’s Department of Trade and Industry (2002) developed a 

strategy that sets out the government’s analysis, options, and proposals for offshore 

development. The conclusion of the consultation was to launch a strategy for offshore 

wind farms that will: 

• Establish a site allocation process that promotes efficient development; 

• Use strategic environmental assessment to guide the pattern and scale of 

development; 

• Ensure proper evaluation of impacts through strategic planning and consenting 

processes; 

25
• Provide for monitoring, mitigation, and control of individual and cumulative 

impacts; 

• Deliver consistent and transparent regulatory decisions in an efficient manner. 

The program developed by the United Kingdom is proactive and considers potential 

development across a broad area. Such planning, if implemented along the Gulf Coast, 

would allow for a comprehensive analysis of wind-energy development and thus result in 

identification of specific locations that could support wind development in an 

economically viable and environmentally acceptable manner. This process also allows for 

development of a true cumulative impact assessment of likely environmental impacts, 

and leads to comprehensive mitigation as warranted. 

2. Research and monitoring 

To minimize the potential risks from wind turbines, it is important to first assess what 

those risks are. Prior to the development of the first large commercial wind farms in 

North America, protocols and methodologies for assessing risks to birds within wind 

resource areas had not been developed. Assessments of other potential environmental 

impacts, such as impacts on habitat and animal movements and visual and noise impacts, 

were minimally considered. 

During the early years of wind farm developments, specifically in California, it became 

apparent that bird collisions, especially raptors, with wind turbines were occurring. 

Approaches to assessing potential environmental impacts needed to be developed. 

3. Initial site selection and permitting 

The National Wind Coordinating Committee (NWCC), a collaborative of representatives 

from the environmental community, wind energy industry, state legislatures, state utility 

commissions, consumer advocacy offices, green power marketers, and federal and state 

governments, was established in 1994 to support the development of wind power. The 

NWCC Web site is www.nationalwind.org/. The Siting Subcommittee of the NWCC was 

formed to address wind generation siting and permitting issues. This subcommittee 

prepared a collaborative document, entitled Permitting of Wind Energy Facilities: a 

Handbook (www.nationalwind.org/publications/permit/permitting2002.pdf) to provide 

guidance in evaluating wind projects for all stakeholders. Some aspects of wind facility 

permitting closely resemble permitting considerations for any other large energy facility 

or other development project. Others are unique to wind generation facilities. Unlike 

most energy facilities, wind generation facilities tend to be located in rural or remote 

areas and are land-intrusive rather than land-intensive. Thus, they may extend over a very 

large area and have a broad area of influence, but physically occupy only a small area for 

the turbine towers and associated structures and infrastructure (e.g., roads, transmission 

lines). The rest of the land may be used for other activities. 

This NWCC handbook outlines the many factors that must be considered when 

permitting a wind generation facility, including (but not limited to) land use, noise, birds 

26
and other biological resources, visual resources, soil erosion and water quality, cultural 

resources, and socioeconomic considerations. Permitting processes that result in timely 

decisions, focus on the critical issues early, involve the public, and avoid unnecessary 

court challenges will enable wind generation to compete with other energy technologies 

and provide a diverse supply of energy. 

As summarized by the National Wind Coordinating Committee 

(www.nationalwind.org/events/offshore/2003/summary.pdf), wind power developers in 

North America are beginning to look offshore for greater wind resources and lower costs. 

As this is a new application for wind power in the United States, the NWCC noted that 

background information is needed about environmental, technical, economic, and 

political issues associated with offshore developments. Some of this information can be 

gathered from Europe as researchers there have been working on offshore wind energy 

development for the past decade. However, each situation varies and thus local factors 

need to be taken into account. 

4. Sampling protocols 

Sampling protocols and methods of quantifying bird fatalities in the field must be 

rigorous and scientifically valid. Failure to establish rigorous protocols and methods 

results in data sets that are subject to criticism and are not ideal for determining how to 

reduce wildlife fatalities in wind developments. 

The NWCC Wildlife Workgroup (formally the Avian Subcommittee) formed to address 

avian interactions with wind developments. It also identifies research needs and serves as 

an advisory group. To address differences in methodologies, lack of adequate control or 

baseline data in existing studies, and the resulting lack of interstudy comparability, the 

NWCC adopted a consensus guidebook titled Studying Wind Energy/Bird Interactions: A 

Guidance Document 

(www.nationalwind.org/publications/wildlife/avian99/Avian_booklet.pdf). The document 

provides a comprehensive guide to standardized methods and metrics to determine 

impacts to birds at existing and future wind farm sites. A stated purpose of the guide is to 

promote efficient, cost-effective study designs that will produce comparable data and 

reduce the overall need for some future studies. 

The Guidance Document identifies three levels of surveys of increasing intensity that 

should be applied to a proposed or developing wind development. Although focused on 

birds, these general guidelines can be applied to most aspects of the environment. “Site 

evaluation” or “reconnaissance” surveys are relatively nonrigorous and use primarily 

published literature and nonpublished reports, expert opinions, and other sources of 

information to make a first determination as to whether a proposed site will likely have 

environmental problems. Such reconnaissance surveys are cursory in nature but should 

help eliminate problematic sites from further consideration. If the reconnaissance survey 

indicates that the site should be suitable for development, then a “level 1” protocol is 

indicated, in which more intensive and quantitative onsite surveys occur, usually for a 

minimum of 1 year prior to a decision to proceed with development. Such level 1 surveys 

27
include onsite sampling of wildlife movements and other activities (e.g., foraging and 

nesting), quantification of the presence and abundance of sensitive species, and 

development of projections on potential bird and bat fatality levels based on risk 

assessment. If a decision is made to proceed with development after level 1 surveys have 

been evaluated, then the data set also serves as the “before” data to be compared with 

changes in environmental conditions following (“after”) development. In rare cases, the 

results of a level 1 study indicate that more intensive study is necessary, such as when the 

presence of a legally protected, threatened, or endangered species is located. 

The methodology used to conduct fatality searches will vary, dependent on the terrain 

and rigor required to adequately assess a site. Often the level of rigor is dictated by the 

budget available for the task. Ideally, the appropriate budget will be allocated to conduct 

the level of work required for the specific site under consideration. Search methods have 

been developed and have proved very successful under research studies funded by the 

Department of Energy’s National Renewable Energy Laboratory. These search methods 

have been developed for both flat and steep terrain. 

Additionally, other efforts are ongoing to increase the guidance available for placing and 

operating wind developments. For example, the U.S. Fish and Wildlife Service (USFWS) 

released a document entitled Interim Guidelines to Avoid and Minimize Wildlife Impacts 

for Wind Turbines (10 July 2003). The stated intent of the USFWS was to have experts 

on wildlife-wind turbine interactions evaluate these guidelines over a 2-year period and 

provide comment to the USFWS; a revised document would then be prepared (but is not 

available at this writing). The Wildlife Workgroup will also be developing a companion 

document to the guidance document that will focus on nocturnal species (birds and bats). 

And, several states have or are in the process of developing their own standards or 

guidelines/requirements for wind developments (e.g., Maryland, Michigan, Washington, 

Virginia, and California). 

Many European countries limited the size of initial off-shore developments so careful 

environmental analysis could be conducted before implementing full-scale projects. For 

example, the United Kingdom initially limited offshore wind farms to 30 turbines to 

reduce environmental and visual impacts, and to ease the cost of decommissioning and 

dismantling when problems arise. Now, commercial developments (over 1000 MW) are 

in operation. 

5. Risk reduction 

a. Wind farm operation 

Recognition of the potential avian fatality risk has influenced the selection criteria used in 

developing some new WRAs. Along with providing a framework for the development of 

more robust experimental field design, use of standardized protocols (as reviewed above) 

has greatly enhanced researchers’ ability to compare and analyze data among studies 

from various WRAs. 

28
Decreasing operation time of problem turbines or WRAs has been suggested as a risk 

reduction measure. Critical shutdown times could be seasonal (e.g., during migration 

periods) or based on inclement weather or nighttime periods when visibility is reduced. 

For example, permitting requirements for a new wind development in Maryland included 

the option for restricting turbine operations if bird fatalities were found to occur during 

peak migration periods. Economic consequences of any kind of adjustments to operation 

time should be considered prior to site construction so that the developer can make a 

feasibility assessment. Most of the newer wind turbines in the Altamont Pass repowering 

areas will increase operation time by as much as 55%. The effect that such an increase in 

operating time will have on bird fatalities is unknown and deserves study. As noted 

above, some European governments limit the size of wind developments to ease the 

financial ramifications of closing a development. 

Design and maintenance characteristics of road and structures may indirectly contribute 

to higher bird fatality rates by increasing prey densities. It has been suggested that 

vertical and lateral edges and other features associated with roads, turbine pads, and 

maintenance areas may create suitable burrow sites for raptor prey in the vicinity of wind 

turbines, with a corresponding increase in raptor foraging activity. Newer facilities that 

are built with larger, more-efficient turbines require fewer roads and have a greater 

amount of space between them. In addition, many of the newer facilities have 

underground distribution lines, greatly reducing the likelihood of wire collisions and 

electrocutions. Offshore developments in Europe manage the movement of maintenance 

crews to minimize disturbance to birds and other animals. 

b. Turbine characteristics and location 

Lights seem to play a key role in attracting birds, and the lighting of tall structures 

appears to contribute to avian fatalities. Illuminating other taller aerial structures to make 

them more visible to aircraft has increased bird fatalities. Migratory species generally 

migrate at night and appear to be most susceptible to collisions with lit towers on foggy, 

misty, rainy, low-cloud-ceiling nights. Passerines migrating at night during poor visibility 

conditions appear to be particularly susceptible. Solid or blinking red lights seem to 

attract birds on foggy, misty nights more than white strobes, which may flash every 1–3 

seconds. Preliminary research suggests that the longer the duration of the “off” phase, the 

less likely a light is to attract birds. The advent of turbines with longer blades that are 

mounted on tall towers could require the use of warning lights for aircraft in certain 

locations. 

Studies indicate that tower placement is a site-specific phenomenon, but several key 

conclusions have been found: (1) irregularly spaced turbines might increase fatalities 

because birds try to negotiate the apparent gaps between turbines; (2) turbines placed 

close to the edge of ridges show higher fatality rates because raptors often hover in such 

locations; and (3) turbines placed near a gully have higher fatalities because birds often 

use these locations as flight paths. 

29
Although no research has been conducted on auditory deterrents to birds approaching 

wind turbines, audible devices to scare or warn birds have been used at airports, 

television towers, utility poles, and oil spills. Most studies of auditory warning devices 

have found that birds become habituated to these devices. Birds do not hear as well as 

humans (Dooling 2002), and minor modifications to the acoustic signature of a turbine 

blade could make blades more audible to birds, while at the same time making no 

measurable contribution to overall noise level. Under certain conditions (e.g., high wind), 

birds might lose their ability to see a turbine blade before they are close enough to hear 

the blade. At present there is no research underway that tests the effects of auditory 

deterrents, and because of the low likelihood of developing a successful application, none 

is planned for the foreseeable future. 

Motion smear, which makes the blade tips of wind turbines appear transparent at high 

speeds, could be reduced under laboratory conditions. Results suggest that a single, solidblack blade paired with two white blades (inverse blade pattern) could be effective at 

reducing visual smearing of blades. However, motion smear and a very narrow blade 

profile encountered when approaching from the side could be very risky for birds. One 

potential solution is a rectangular attachment to the outer tip at right angles to the long 

axis of the blade. The visibility and practicality of these attachments have not yet been 

evaluated (Hodos 2003). 

c. Habitat management 

The density of raptors at the Altamont Pass WRA is, at least in part, a result of high prey 

availability. San Gorgonio and Tehachapi WRAs, California, have lower prey densities, 

lower raptor densities, and lower per-turbine fatality rates. Prey densities appear to be 

highest at disturbed sites such as roads and turbine pads, the latter of which would 

exacerbate collision risk. Reducing prey populations within the vicinity of wind turbines 

might reduce high-risk foraging activities for raptors. Suggested methods include countysponsored abatement programs, reduced grazing intensities, and revegetation with higherstature plants that pocket gophers and ground squirrels tend to avoid. These measures, 

however, could impact other populations, including special-status species such as the San 

Joaquin kit fox, burrowing owl, and badger. 

It has been suggested that in areas where high densities of gopher burrowing systems are 

found, controlling populations in the immediate vicinity of wind turbines could be 

effective. They cautioned, however, that small mammal abatement efforts by ranchers in 

surrounding areas could exacerbate the effect of burrow clusters in the vicinity of 

turbines by increasing the focus of raptor foraging. This effect occurs when there is rapid 

recolonization and higher-than-average densities of gophers on edges of abatement areas. 

Research would have to evaluate reduced grazing or revegetation with higher structure 

plants to determine its effects on fire management, watershed protection, and other landmanagement practices. 

Habitat modification to reduce prey densities has been discussed as a possible avian riskreduction technique. There have been some efforts to reduce ground squirrel populations 

30
in portions of the Altamont Pass WRA, but no results of the effects on reducing raptor 

mortalities have been published to date. The effects of a widespread control program 

would have to take into account the effects on other wildlife, such as protected species 

that prey on ground squirrels or depend on their burrows for nesting and cover habitat. 

Widespread use of rodenticides or other measures to remove prey may prove to be 

controversial and costly. Feasibility of more benign habitat modification measures—such 

as manipulation of annual grassland grazing practices or conversion to perennial 

grassland—may be worth studying. However, any reduction in habitat quality would 

likely cause an ultimate, although indirect, negative impact on birds. For example, 

although reducing prey in wind developments might lower bird fatalities, it could also 

result in bird starvation or fatalities in other locations. It was shown in The Netherlands 

that turbines adjacent to the Wadden Sea showed a higher rate of bird kills compared to 

turbines in upland areas. These higher kills appeared to be related to the large number of 

birds in and around the sea compared to the upland locations. Unfortunately, virtually no 

information is available on fatalities at offshore wind farms in Europe. 

d. Turbine treatments 

Effective visual treatments could provide a cost-effective method to reduce risk from 

turbines determined to cause fatalities. Laboratory and field tests of treatments that make 

turbine blades more conspicuous to raptors and other birds are needed. 

6. Research needs 

The priority research objective is to quantify seasonal occurrence, abundance, and 

location of bats and birds along the LGC. Specifically, research should focus on the 

following issues. 

• The location, magnitude, and timing of movements of raptors during fall 

migration 

o Because of the substantial numbers of raptors migrating through the LGC, 

and the known rates of raptor fatalities in wind facilities, there is potential 

for substantial raptor fatalities at new wind installations. Although “hawk 

watch” locations and data sets are available, they are few in number and 

should be substantially expanded to gain a better understanding of the 

extent of raptor migration. But with nearly 1 million broad-winged hawks 

passing by a single observation station, the potential for substantial 

seasonal fatalities exists. 

• The location, magnitude, and timing of movements of bats and birds during spring 

and fall migration 

o It appears that a substantial number of passerines and other nonraptorial 

birds move along the LGC during migration, likely staying close to the 

coastline and along the nearshore area. Such behavior could increase the 

risk for these species relative to direct flights out over the Gulf. 

• Identification of locations where rare and endangered species (bats and birds) 

occur during breeding and nonbreeding periods 

31
o A number of the raptorial species that migrate through the LGC are rare or 

threatened/endangered in Texas and other regions of the United States, 

including the peregrine falcon, Swainson’s hawk, osprey, and bald eagle. 

• Identification of any special environmental features that could concentrate bats 

and birds (e.g., roosting caves for bats, riparian areas for birds) 

o Surveys should be conducted to identify any potential bat roosts, foraging 

areas (e.g., open water), locations of concentrated bird activity (e.g., 

springs, riparian areas), and other environmental features that could 

concentrate bats and birds near proposed wind facilities. 

It is not possible to identify specific locations or species for study in the absence of 

knowledge of likely sites for wind-energy developments. Thus, wind-energy developers 

are encouraged to work closely with bat and bird ecologists in conducting initial 

screening of potential development sites. Such screenings are frequently termed 

“reconnaissance” surveys, and are designed to eliminate areas of high bat or bird use 

from being developed as wind-energy facilities. Reconnaissance surveys need to be of 

sufficient intensity and duration to adequately quantify bat and bird use of a potential 

development site during all seasons of the year. Brief visits to potential development sites 

are inadequate. In all cases, what are frequently termed “Phase I” surveys should be 

initiated at all sites likely to be developed. Phase I surveys build on reconnaissance 

surveys and incorporate more intensive study of the distribution and abundance of bats 

and birds. Phase I surveys incorporate rigorous counts of all bird species using methods 

appropriate to major bird types (e.g., songbirds, raptors, and waterfowl). Methods for 

quantifying bat use of potential wind developments are undergoing a rapid growth, and 

include radar, acoustic recordings, thermal imagery, and other techniques. The “metrics” 

document (Anderson et al. 1999) produced by the NWCC is being revised to incorporate 

many of the techniques available for bats and birds. 

F. Acknowledgments

I appreciate the suggestions and guidance provided by Karin Sinclair and Robert 

Thresher of NWCC-NREL on developing this paper. Many people provided review 

comments on earlier drafts, including Bart Ballard, Leonard Brennan, William Kuvleski, 

Ed Arnett, Bonnie Ram, and several anonymous referees. 

32
G. Literature Cited 

Anderson, R., M. Morrison, K. Sinclair and D. Strickland. 1999. Studying wind 

energy/bird interactions: a guidance document. National Wind Coordinating 

Committee/RESOLVE, Washington, D.C. 87 pp. 

Department of Trade and Industry. 2002. Future offshore: a strategic framework for the 

offshore wind industry. Department of Trade and Industry, United Kingdom. London. 

Dooling, R. 2002. Avian hearing and the avoidance of wind turbines. National 

Renewable Energy Laboratory, Golden, Colorado. NREL/TP-500-30844. June 2002. 

Erickson, W. P., G. D. Johnson, M. Dale Strickkand, D. P. Young, Jr., K. J. Serna and R. 

E. Good. 2001. Avian collisions with wind turbines: a summary of existing studies and 

comparisons to other sources of avian collision mortality in the United States. Resource 

Document, National Wind Coordinating Committee, Washington D.C. 62 pp. 

Erickson, W., G. Johnson, D. Young, D. Strickland, R.Good, M. Bourassa, K. Bay, and 

K. Sernka. 2002. Synthesis and Comparison of Baseline Avian and Bat Use, Raptor 

Nesting and Mortality Information from Proposed and Existing Wind Developments. 

Prepared by Western EcoSystems Technology, Inc. for Bonneville Power Administration. 

Cheyenne, Wyoming. 

Exo, K. M., O. Hüppop, and S. Garthe. 2003. Birds and offshore wind farms: a hot topic 

in marine ecology. Wader Study Group Bull. 100:50–53. 

Gauthreaux, S. A. Jr. 1970. Weather radar quantification of bird migration. BioScience 

20:17-20. 

Gauthreaux, S. A. Jr. 1971. A radar and direct visual study of passerine spring migration 

in southern Louisiana. Auk 88:343-365. 

Gauthreaux, S. A. Jr. 1992. The use of weather radar to monitor long-term patterns of 

trans-Gulf migration in spring. Pp. 96-100 in: J. M. Hagan, III and D. W. Johnston (eds.), 

Ecology and Conservation of Neotropical Migrant Landbirds. Smithsonian Institution 

Press, Washington, D.C. 

Hodos, W. 2003. Minimization of motion smear: reducing avian collisions with 

wind turbines. National Renewable Energy Laboratory, Golden, Colorado. NREL/SR500-33249. August 2003. 

 

Lincoln, F.C., S.R. Peterson, and J.L. Zimmerman. 1998. Migration of birds. U.S. 

Department of the Interior, U.S. Fish and Wildlife Service, Washington, D.C. Circular 

16. Jamestown, ND: Northern Prairie Wildlife Research Center Online. 

www.npwrc.usgs.gov/resource/birds/migratio/migratio.htm (Version 02APR2002). 

33
Morrison, M.L., and K. Sinclair. 2004. Wind energy technology, environmental impacts 

of. Pages 435-448 in Encyclopedia of Energy. Volume 6. Elsevier, Inc., St. Louis, MO. 

National Wind Coordinating Committee (NWCC). 2002. Permitting of wind energy 

facilities: A handbook. NWCC c/o RESOLVE, Washington, D.C. 50 pp. 

Russell, R.W. 2005. Interactions between migrating birds and offshore oil and gas 

platforms in the northern Gulf of Mexico: Final Report. U.S. Dept. of the Interior, 

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. OCS 

Study MMS 2005-009. 348 pp. 

Smallwood, K.S., and C. Thelander. 2005. Bird mortality at the Altamont Pass Wind 

Resource Area: March 1998-September 2001. National Renewable Energy Laboratory, 

Golden, Colorado. NREL/SR-500-36973. August 2005. 

Winkelman, J. E. 1985. Vogelhinder door middlegrote windturbines—ver vlieggedrag, 

slachtoffers en verstoring (Bird impact by middle-sized wind turbines—on flight 

behavior, victims, and disturbance.) Limosa 58:117-121. (In Dutch; English summary) 

Winkelman, J. E. 1990. Nachtelijke aanvaringskansen voor vogels in de Sepproefwindcentrale te Oosterbierum (Fr.) (Nocturnal collision risks for and behavior of 

birds approaching a rotor in operation in the experimental wind park near Oosterbierum, 

Friesland, The Netherlands; English summary). Rijksinstituut voor Natuurbeheer, 

Arnhem. RIN-Rapport 90/17. 

Winkelman, J. E. 1992. De invloed van de Sep-proefwindcentrale te Oosterbierum (Fr.) 

op vogels, 1. Aanvaringsslachtoffers (The impact of the Sep Wind Park near 

Oosterbierum [Fr.], The Netherlands, on birds, 1. Collision victims.) ENGLISH 

SUMMARY ONLY. Pages 69-71. DLO-Instituut voor Bos- en Natuuronderzoek, 

Arnhem, Netherlands. RIN-Rapport 92/2. 

Winkelman, J. E. 1994. Bird/wind turbine investigations in Europe. Pages 43-47 in: 

Proceedings of the National Avian-Wind Power Planning Meeting, Lakewood, Colorado, 

20-21 July 1994. Proceedings prepared by LGL Ltd., environmental research associates, 

King City, Ontario. Author's address: Birdlife/ Vogelbescherming Nederland, 

Driebergweweg, The Netherlands. 

Winkelman, J.E. 1995. Bird/wind turbine investigations in Europe. Pages 43-47 in

Proceedings of National Avian-Wind Power Planning Meeting, Lakewood, Colorado. 

National Renewable Energy Laboratory, Golden, Colorado. NREL/SP-441-7814. April 

1995. 

34
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1. REPORT DATE (DD-MM-YYYY)

June 2006 

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Subcontract report 

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22 November 2000 – 31 October 2005

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Bird Movements and Behaviors in the Gulf Coast Region: Relation 

to Potential Wind Energy Developments 

5c. PROGRAM ELEMENT NUMBER

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NREL/SR-500-39572 

5e. TASK NUMBER

WER6.3401 

6. AUTHOR(S)

M.L. Morrison 

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Department of Wildlife and Fisheries Sciences 

Texas A&M University 

College Station, TX 77843-2258 

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NREL 

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NREL Technical Monitor: Karin Sinclair 

14. ABSTRACT (Maximum 200 Words)

The purpose of this paper is to discuss the possible impacts of wind development to birds along the lower Gulf Coast, 

including both proposed near-shore and offshore developments. The report summarizes wind resources in Texas, 

discusses timing and magnitude of bird migratrion as it relates to wind development, reviews research that has been 

conducted throughout the world on near- and offshore developments, and provides recommendations for research 

that will help guide wind development that minimizes negative impacts to birds and other wildlife resources. 

15. SUBJECT TERMS

wind development; environmental impacts; offshore wind energy; birds; bats; wildlife 

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