Avian Radar Project
Making Wind Power Wildlife Friendly

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Impacts of Wind on Wildlife

How to Make Wind Power More Wildlife Friendly


Wind Power Basics

Wind TurbineWind turbines. Photo by USFWS

Wind turbines are large structures that often stand around 100 m (328 ft) tall with generally 3 turbine blades extending out 50 m (164 ft) from the central nacelle. This brings the approximate total height of the structure to 150 m (492 ft). This is on average, there are much larger turbines that extend over 200m (656 ft) in total height. These turbine blades are pushed by the wind and generate electricity, up to 8 MW for some turbines at peak performance. That is enough to power around 8,000 homes. The airspace through which the turbine blades spin is called the rotor swept zone (RSZ). The RSZ is generally the heights from 50-150 m but depends on the actual size of the turbines. Spinning turbine blades can reach speeds of almost 200 mph at the tips and the area spanned by the blades can cover an area that exceeds the size of a football field. Wind farms may have hundreds of turbines placed 0.5 - 1 km apart, potentially affecting a large area of the landscape. Wind farms are placed in the windiest area and often the areas with the highest wind speeds are used heavily by birds and bats, who

use the winds to their advantage while migrating.


Prothonotary Warbler Prothonotary warbler.

Photo by USFWS

Wind Power and Migrants

As they migrate, birds and bats can be killed by impacts with the spinning turbine blades. Estimates of bird fatalities from impacts with wind turbines range from 140,000 to 573,000 birds annually (Loss et al. 2013, Smallwood 2013). Birds killed range in size from small warblers to large eagles and vultures and includes many endangered species. In the Great Lakes, endangered species that may be threatened by wind power include the Kirtland's warbler (Steophaga kirtlandii) and the piping plover (Charadrius melodus) as well as the federally protected bald eagle (Haliaeetus leucocephalus) and golden eagle (Aquila chrysaetos). Additionally, many bird species are protected by federal law under the Migratory Bird Treaty Act (1918). Many bird fatalities occur in large events on single nights due to environmental conditions like rain or fog, often coupled with lighting on the facilities accidentally left on, or other factors.


When siting a wind energy facility, areas with high sustained speeds are usually preferred. However, these areas are also where birds and bats have evolved to migrate though, often using the high wind speeds to assist with their migration. Migrants will adjust their flight heights to match the most favorable wind speeds and directions and may wait for favorable conditions to occur before migrating at all. Favorable wind conditions may not exist everywhere and could lead to concentrating migrants in an area, such as along the shorelines of the lakes. These maps examine the current national and global wind conditions.


It is estimated that more than 600,000 bats were killed by wind turbines in 2012 (Hayes 2013, Smallwood 2013). The majority (approx. 75%) of these fatalities were in the handful of long distance migrants like the hoary bat (Lasiurus cinereus), silver-haired bat (Lasionycteris noctivagans), and the eastern red bat (Lasiurus borealis) (Kunz et al. 2007, Cryan 2011). Short distance migrants, including endangered species such as the Indiana bat (Myotis sodalis),

Indiana bat Indiana bat.

Photo by USFWS

are also impacted. Bats tend to fly at lower altitudes than birds when migrating, possibly because they feed while they are migrating. They also may be attracted to the turbines or attracted to the insects that are drawn to the turbines or turbine lighting. For these reasons, bats have tended to be affected more by wind turbines than birds have been, with a higher number of fatalities spread among a smaller number of species.


Some eastern North American bats have recently been affected by White Nose Syndrome, a fungal disease that has caused a vast reduction in hibernating bat populations. In some cases, mortality of up to 95% in hibernacula has been recorded. This has led to several species being considered for listing under the Endangered Species Act. With the threat to hibernating bats from White Nose Syndrome, and the vast majority of bats killed by wind turbines being migratory bats, bats are being threatened on two fronts. Losing this group of animals would result in large increases in crop pests and biting insects like mosquitoes that spread disease as bats eat tons of
these insects every night.


Wind Turbine

Wind turbines under construction. Photo by Dan Nolfi/USFWS

Projected Increase in Wind Power

In 2012, over 60 GW of power was generated by wind facilities across the United States. The Department of Energy is calling for an increase in wind power to represent 20% of the power generated across the United States by 2030. That represents about a five-fold increase to over 300 GW. Some individual states have even higher goals for renewable energy, such as California, Hawaii, and Colorado. An increase in bird and bat fatalities will likely accompany such an increase in wind power generation if we do not take steps to reduce the impact of wind facilities on wildlife (Loss et al. 2013). These fatalities combined with increasing habitat loss, disease, and climate change may put many more species at risk of extinction than we already have listed under the Endangered Species Act. Gaining the benefits of reduced greenhouse gases from the renewable energy source of wind does not mean that turbines are entirely environmentally friendly. However we now have the opportunity proactively to reduce the impact that turbines will have on wildlife for present and future generations as we pursue cleaner energy sources. A map of over 47,000 onshore wind turbine sites in the U.S. (as of July, 2013) is available from USGS, including details on the height and type of turbines.


Ways to Reduce Impact on Wildlife

Studying Wildlife

USFWS Personnel with Acoustic Monitor. Photo by Andrew Horton/USFWS

Many wind facilities have very low impacts to birds and bats, but there are some that can have very high fatality rates. Determining what factors are different between areas with high fatality rates and low fatality rates can help us to install wind facilities in areas where they will have the least impact. One way to try and determine if an area may have a high risk to birds and bats is to study how many are migrating through an area before the turbines are built. If there are high numbers in an area, that would seem to indicate a higher potential risk of fatalities. One of the main goals of the Avian Radar Project is to find these areas that have high concentrations of migrants and inform the wind industry of the risks of building in those areas. By informing decisions about the impact to wildlife a wind farm might have in an area before turbines are built, a great deal of time, money, and lives of wildlife can be saved.


In some cases, and for wind facilities that are already built, placing turbines in another area may not be feasible. In that case, there are methods that can be used to reduce the impact of a wind farm on migrants. One example would be to turn off the turbines during the entire migration season. Migrants are usually moving through for over two months each spring and fall, so this may be too long of a period to be acceptable to the wind facility operator.


Studying Wildlife

USFWS Personnel Conducting Bird Survey. Photo by Becky Horton/USFWS

Another option is to use wind cut-in speeds. This is a wind speed above which the turbine is operational and below which it is stopped. Our study has shown that when the wind speed is above 6.9 m/s (~15 mph), over 99% of bat activity has stopped in some locations. This allows for the wind facility to generate power at times when bats are likely not flying. Additional research is being looked into with a temperature cut-in level, where below a certain temperature bats are not likely to be active. Other research is looking into the use of deterrents which might be useful for mitigating new and existing wind facilities.


By using some of these methods, impacts to migrants can be reduced and we can still achieve the benefits of generating power from the wind. By combining the migration season dates with the cut-in speeds in some cases, the reduction in mortality of bats can be over 90% with a loss in power output only around 1% (Arnett et al. 2011).


For birds, limiting lighting on and around wind turbines and buildings seems to be helpful for reducing fatalities. Following the USFWS Voluntary Land-based Wind Energy Guidelines may help to prevent large-scale fatalities in birds.

Last updated: February 19, 2014