While the wind energy industry continues to develop, wind turbines themselves grow as well. Today, wind turbines can stand between 200 and 260 feet tall, as opposed to the earlier models that were between 60 and 80 feet tall. This drastic change in size has resulted in a higher influence on the surrounding bat and avian species, as well as their habitats. The blades of a wind turbine typically spin at a rate of 132 to 182 miles per hour, which produces significant alterations to the surrounding air and wind conditions. Not only do the overall size of a turbine and the speed of its blades produce risks for birds and bats, but the speed at which the turbines spin is also highly influential.
As part of a general analysis of the interactions between wind turbines and bat and avian species, the National Wind Coordinating Collaborative (NWCC) produced a document that addressed general questions and concerns relating to these interactions. The NWCC is a group of stakeholders that was formed in 1994 with the goal of promoting “environmentally, economically, and politically sustainable” projects within the wind energy sector. Their document was published in the spring of 2010, and is entitled “Wind Turbine Interactions with Birds, Bats and their Habitats: A Summary of Research Results and Priority Questions”.
Observations and analyses of wind energy projects across North America are incorporated in this document. Discussions on key impacts to both species and their habitats are addressed, as well as the current research results and the gaps that remain in understanding the interactions between wind energy and bat and avian species.
The document presents its findings in a three-tiered outline, and our discussion of the document will follow suit. The tiers are outlined and discussed below.
“What Studies Have Shown”
Research findings that provide a picture on what developers and researchers currently know about the interactions between wind energy and bat and avian species are presented in this section. These findings are a conglomeration of research methods and protocols from studies across North America. The extent of analysis for such studies has improved drastically since the original fact sheet that was published by the NWCC in 2004.
The first issue addressed is the direct and indirect effects on mortality rates. The document shows that mortality rates of raptors at wind turbine sites averages between 4 and 14 individuals per turbine per year. This is argued to be insignificant, especially in comparison to the increased bat mortality rates. Most bat fatalities are recorded during the spring and fall migration seasons. However, further research on bat population distributions and migration patterns are required to further understand the extent of the effects on bat species. It should be noted that the differences amongst regional conditions produces a high variability of mortality rates. Detailed graphs of these variations are found on page 3 of the fact sheet.
Songbirds are of high concern, as roughly three quarters of the total bird fatalities accounted for at wind turbines. Although fatalities are substantially lower than other anthropogenic threats to songbirds (vehicles, infrastructure, pesticides, etc), fatalities from turbines are likely to increase as wind turbines continue to be developed.
The Federal Aviation Association (FAA) regulations on the lights used to illuminate wind turbines are not found to increase mortality rates for either bat or avian species.
For raptors, the best way to reduce direct impacts is to place wind turbines away from areas that raptors use. Such areas would include cliffs and ridges. Simply moving turbines away from these sites would avoid significant raptor fatalities.
“What is Less Understood”
The NWCC addresses a critical issue within wind energy projects: the current methods of using pre-construction research to predict post-construction fatalities are currently insufficient. The results of post-construction monitoring infrequently reflect the pre-construction predictions. These differences require a refurbishment of the way that we use pre-construction research to predict future fatalities.
Although the following observations have been argued to be true, they have yet to be concretely proven. It has been argued that placing turbines farther away from prey populations will result in fewer raptor fatalities, as there will be a reduction in raptor use. Furthermore, use of larger turbines results in smaller wind energy developments and may reduce raptor collisions. In addition, although little research exists on coastal wind energy developments, current research argues that waterbird and waterfowl fatalities are relatively low.
In regards to bat species, the following observations suggest specific impacts but are still loosely understood. For example, the influence of weather patterns is considered to be a strong factor in influencing bat mortality, however, further research is required. Current research shows that adult male bats may be at a particularly higher risk than other bats. Although this interaction is poorly understood, it is currently argued that late summer/early fall breeding patterns may entice male bats to congregate around wind turbines with the intent of attracting females.
“Areas Where Little Is Known”
The biggest uncertainty concerning wind energy is the extent to which it will expand. As the industry continues to grow and more and more wind projects are developed, there will be a growing need for continued research. Because we cannot predict the extent to which wind energy will expand, our understanding of its future effects is impossible to comprehend.
The differences amongst habitat types confound our understanding of favorable development sites. Current research suggests that agricultural sites produce lower migrant songbird fatalities than forested sites. However, this correlation remains unclear.
Barotrauma, a condition that results in internal injuries from sudden changes in air pressure, is still poorly understood as it relates to bats. Because wind turbine blades spin at a high rate of speed, wind vortices are created in their wake and create air pressure changes. These changes produce barotraumas for bats and could be a significant factor in the increased mortality rates. However, current studies are struggling to assess the extent of barotraumas on bats.
Furthermore, it still remains unclear on how topography and other geographical factors affect bat mortality rates. Developing a better understanding of how different habitats produce different interactions between bats and wind turbines could result in methods to place wind turbines out of range of high bat-use areas. In addition, there is a need to understand whether or not bats are attracted to wind turbines, as it is currently assumed that bats congregate around turbines. This possible attraction could be due to a higher concentration of insects, sounds produced by turbines, as well as the bats intents to use turbines as roosting sites.
In conclusion, it is impossible to predict how wildlife will adapt to large wind turbines being placed in their habitats. The ability for wildlife to adjust to new influences in their environment is referred to as habituation. Researchers are currently unsure how species will habituate to wind farms, though it is presumed that wildlife will adapt to at least some extent.
All information and references included in this summary are adapted from what is provided in the NWCC’s “Wind Turbine Interactions with Birds, Bats and their Habitats: A Summary of Research Results and Priority Questions”. Any references are references to the work of the respective authors.
National Wind Coordinating Collaborative (2010, Spring). Wind Turbine Interactions with Birds, Bats and Their Habitats: A Summary of Research Results and Priority Questions. Retrieved from:
https://www.nationalwind.org/assets/publications/Birds_and_Bats_Fact_Sheet_.pdf
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