Comprehensive Assessment of Wind Turbine Effects on At-Risk Bird Populations

Derek Power – Building Construction Technology

Lily Coughlin – Animal Science

Josh Cardin – Planet Soil & Insect Sciences

Wind power is one of the fastest growing branches of the energy industry and is a crucial part of our world’s plan for renewable energy. Wind farms are an incredibly sustainable and clean fuel source. Wind energy does not pollute the air like power plants that rely on combustion of fossil fuels, such as coal or natural gas. Wind energy is also categorized as a form of solar energy so as long as the sun keeps shining and the wind keeps blowing, the energy produced can be harnessed to send power across the grid. In addition to being sustainable and clean, wind farms benefit the economy as well. The cost of generating wind energy is similar to that of fossil fuels (Fehrenbacher, 2015). The industry also creates jobs, and in many cases the farms can be built on existing ranches or farms (“Advantages and Challenges,” 2013). According to the Wind Vision Report, wind has the potential to support more than 600,000 jobs in manufacturing, installation, maintenance, and supporting services by 2050 (“Advantages and Challenges,” 2013).

Despite the many benefits of wind farms, people often argue against their development by claiming that turbines have a detrimental effect on bird populations. The opponents of wind energy claim that birds are being struck by the propellers and populations are declining as a result. There are organizations dedicated to slowing down the development of wind energy as a renewable form of energy due to the alleged impacts on bird populations, such as Save the Eagles International. The organization’s website shows graphic images of dead eagles, reportedly after being struck by the propellers of wind turbines. And while those claims certainly are valid, all current scientific literature shows that while wind turbines certainly do contribute to mortality rates of bird populations, it is statistically insignificant compared to other anthropogenic causes. Zimmerling et al. (2013) found that other industrial structures, including residential houses, skyscrapers, power lines, cars, and even domestic house cats are a major cause of mortality to birds and dramatically outweigh mortality caused by wind turbines. Erickson et al. (2014) found that wind turbines estimated to cause upwards of 368,000 bird deaths annually in the United States by while 3-6 billion birds die from other anthropogenic causes. A website called shows an estimate of 2.4 billion deaths by cats and 400,000 by turbines. Also from Erickson’s et al. (2014) research, only .016% of bird species of conservation concern were affected. Longcore et al. (2013) lead research on birds that collided into communication towers at 107 different locations throughout central and eastern North America. With 239 species making up the quarter million bird fatalities, 97% were passerines, consisting of over half being warblers (Erickson’s et al. 2014; Longcore et al., 2013).

Despite available literature supporting the idea that bird populations are not significantly affected by wind turbines (De Lucas et al., 2004), there is no reliable method of predicting impacts of wind farms on bird populations prior to construction, and no reliable method of assessing impacts after construction has been completed. The overall impact of wind turbines on bird species is inconsistent between studies. Many wind farms are required to perform pre-construction assessments to predict the impact on birds in the area, but many of these studies do not include effects on important bird species. Post-construction assessments on the actual impact of birds are not required for all wind farms in the United States, which means that the impacts on bird populations is completely unknown in these cases. Impact studies use different methods for testing in both pre- and post-construction assessments. This leaves the potential for significant impacts to certain species.

A major issue with assessing impact on bird populations is the lack of consistency in how studies are conducted. Johnston et al. (2014) performed their study by observing birds from boats and from offshore platforms, and identifying the heights at which they flew through photographs and trigonometry. Zimmerling et al. (2013) determined impacts on birds based on reports filed by local government agencies and the wind developers themselves. Grodsky et al. (2013) searched on foot at a wind farm for carcasses of dead birds to indicate mortality. De Lucas et al. (2004) and Garvin et al. (2011) both had researchers stationed along transect lines using binoculars to observe flight behavior and record abundance of birds in areas where wind farms were going to be built. All of these methods have their own shortcomings and in turn have a wide window of opportunity for error. In addition, there are many other aspects of conducting studies that can vary. The length of study, the time of year the study is conducted and observer effort are all things that vary significantly between studies. All of these variables combined make predicting impacts of wind turbine farms challenging, as well as assessing impacts after construction has been completed.

Certain bird species are typically more at-risk than others. At-risk species could be defined as endangered or threatened species, as well as long-lived species. Endangered and threatened species are those that are protected under the Convention on the International Trade of Endangered Species (CITES) and are thus protected under the Endangered Species Act. These are international agreements that protect certain species whose populations have declined or are at-risk of declining to the point of extinction. Habitat loss can also contribute to a species being protected by CITES. Long-lived species are another concern because of their specific life-history traits that include reaching sexual maturity at older ages, infrequent or inconsistent breeding periods, and longer pregnancies. Long-lived species have very slow population growth rates, so losing even a few individuals can detrimentally affect the population (“Birds”). Due to the potential for bird mortality caused by wind farms, the United States should implement mandatory pre- and post-construction assessments to more accurately determine the impact upon at-risk species.

To properly assess potential impacts on at-risk bird species from wind turbines, the United States needs to require developers to conduct pre-construction surveys of the proposed land to predict effects. These pre-construction assessments will first determine what species utilize the particular area and specify what species are considered to be at-risk (i.e. protected under Endangered Species Act or long-lived species). Once the species are identified by U.S. Fish and Wildlife Services as birds of conservation concern, studies should be carried out to determine how each of those species utilizes the habitat, such as breeding habitat, feeding, nesting, or migration routes. If it is determined that the particular area is vital habitat for any at-risk species, construction should not be permitted and a new site should be identified. If the area is important habitat for nesting or breeding exclusively, timing of construction should be taken into consideration so that these natural activities will not be disrupted. However, if it is predicted that at-risk species will not be affected, construction can continue.

Currently, Europe has mandatory Early Impact Assessments (EIA) to determine the effects on the environment. The reports suggests how to reduce environmental impacts, and also provide insight on public approval of the project and are mandatory by the EIA Directive according to the European Commission. While this is a good base for assessing environmental effects, more specific assessments that determine impacts on birds should be carried out. Experts Ferrer, de Lucas, Janns, Casado, Munoz, Bechard, and Calabuig (2012) believe these assessments are not as effective as intended to be, because each wind farm location and the surrounding bird populations are extremely variable.The United States should use Europe’s EIA as a template for creating a program which will determine wind farm impacts on birds, then further expanding the program to include recent/future technological advances to conduct post-construction surveys as well.

Once construction is completed and the wind farm is operating, post-construction assessments should be done to compare the predictions from pre-construction surveys to post-construction impacts, which will assess actual impact on bird species. If the pre-construction assessments either under- or over-estimated impacts, then pre-construction survey methods should be adjusted in order to get a more accurate prediction. If the post-construction impact assessments show that there are no significant effects on at-risk species, then the wind farm will be deemed a success. However, if mortality is significantly affected by the wind farms then the wind farm must temporarily close until a solution can be reached. There is some research into methods of mitigating effects on bird species, such as radar detecting incoming birds and shutting down turbines (Zimmerling et al., 2013), so if a solution similar to that can be reached the decreases the impact on birds that would be ideal. In addition to decreasing impacts on at-risk species, researching mitigation strategies to decrease effects on bird populations will further our understanding of wind turbines. However if a solution cannot be found and the at-risk populations are negatively affected, the wind farm will need to close. All research suggests that mortality is not significantly affected, so this is highly unlikely. These assessments will allow researchers to more accurately and completely determine effects of wind turbines on bird populations, and will ease the public’s resistance towards investing in wind energy due to potential bird mortality.

The current literature shows that wind farms do not pose a significant threat to any bird species studied (Grodsky et al., 2004). Garvin, Jennelle, Drake and Grodsky (2013) determined that wind farms did not significantly decrease available habitat in areas where an EIA has approved construction. This means that wherever there was an early impact assessment done, that there was no reduction in habitable land availability for at-risk species. Not only have all studies shown that wind farms do not significantly affect bird populations, some species adapted to their altered habitat and are using the areas to their advantage. Raptors have been observed to alter flight behavior by changing direction or height after detecting presence of a wind farm (De Lucas et al., 2004). Scientists in Canada have observed the pink-footed goose nesting and feeding directly under a wind turbine (Zimmerling et al., 2013). The impact of wind farms on birds is so insignificant, if the amount of wind turbines in the United States doubled, the mortality caused by collisions and habitat loss still would not significantly affect birds (Zimmerling et al., 2013). Although the number of wind farms does not have a significant effect on bird populations, the impact can vary depending on the design of the turbines. One study found that wind farms with fewer, larger turbines have less of an effect on bird populations than wind farms with many small turbines (Johnston et al., 2014). De Lucas et al. (2004) determined that taller turbines inhibit bird flight paths and cause a negative impact called the “barrier effect”. Their study found that using shorter turbines can reduce the barrier effect and therefore reduce negative impacts on birds (De Lucas et al. 2004). In addition, having certain crops around the wind turbines can maintain presence of bird species. For example, if there are hedges near a wind farm it will increase food availability for granivores and therefore will increase their presence (Devereux et al., 2008).

Birds are an extremely important part of the ecosystems of which they reside in. Disrupting a population in terms of their mortality rate, habitat availability, and nesting or feeding behaviour not only has negative effects on that particular species but also has cascading effects throughout every trophic level within that ecosystem. A delicate balance exists within natural systems and skewing that in any manner has serious consequences for every other species, whether direct or indirect. In addition, at-risk species in this context includes long-lived species. Larger birds often have life history traits associated with being long-lived, which typically includes raptors and other birds of prey. These species are of particular importance because they commonly are found at the top of the trophic pyramid in any ecosystem in which they are found. As a result, they regulate all species below them. If their populations are disrupted, this has significant cascading effects throughout the entire trophic pyramid within the ecosystem.

While it is true that birds face mortality as a result of wind farm construction, the impact on mortality rates is highly insignificant in comparison to other anthropogenic sources of mortality. Despite current literature supporting these claims, the extent to which at-risk species are impacted at wind farm sites is still largely unknown. There are currently no government requirements to conduct pre- and post-construction assessments at proposed wind farm sites to predict the impact on bird populations or to assess effects after the wind farm has opened. The United States must require pre- and post-construction impact assessments be carried out at wind farm sites. This is necessary in order to protect at-risk species, defined as long-lived or protected under the Endangered Species Act. Without this, the actual impact that wind farms have on birds is largely unknown. The knowledge that accurate information could bring to the renewable energy industry would allow wind farm companies to better protect the species surrounding their facilities and would increase public support, if the public knew that birds were not significantly affected by their presence. This would have an extremely positive impact not only on the birds but on the renewable energy sector and our planet as a whole.



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Devereux, C. L., Denny, M. J. H., & Whittingham, M. J. (2008). Minimal effects of wind turbines on the distribution of wintering farmland birds. Journal of Applied Ecology, 45(6), 1689-1694. doi:10.1111/j.1365-2664.2008.01560.x


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Longcore, T., Rich, C., Mineau, P., Macdonald, B., Bert, D.G., Sullivan, L.M., Mutrie, E., Gathreaux, S.A., Avery, M.L., Crawford, R.L., Manville, A.M., Travis, E.R., & Drake, D. (2013). Avian mortality at communication towers in the United States and Canada: which species, how many, and where? Biological Conservation, 158, 410-419.


Zimmerling, J. R., Pomeroy, A.C., d’Entremont, M.V., & Francis, C.M. (2013). Canadian estimate of bird mortality due to collisions and direct habitat loss associated with wind turbine developments. Avian Conservation and Ecology 8(2), doi:10.5751/ACE-00609-080210




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