|Fig. 1: This is part of the Tomamae wind farm used to study bird fatalities in the northern Hokkaido region. (Source: Wikimedia Commons)|
Although renewable energy sources such as wind turbines produce significant benefits towards the environment, their perception as environmentally friendly unfortunately hides the negative attributes that come with these machines. In particular, wind turbines have been noted as being significant disturbances towards their areas bird and bat populations, as rotor blade and power line collisions have resulted in a reduction in certain species of wildlife.  A typical 200 kW wind turbine has a tower height of 37.5 m, and a width of 25 m due to the rotor blade diameter, however wind turbines recently can produce much more than 200 kW of average power and exceed 80 m in height.  Combine that with the fact that these wind farms have many turbines spread across large sections of open plains, marshland, and ocean, and the result is an area of land that creates many possibilities for bird-machine collisions. Therefore, in order to fully understand the impact the scale of which wind energy has on wildlife, we will observe both a small study on bird fatalities in Hokkaido, Japan, as well as a larger estimation survey on wildlife fatalities from wind energy across the entire United States.
Researchers over the course of 17 months studied 42 wind turbines in a region of northern Hokkaido, as shown in Fig. 1. This wind farm produces roughly 52.8 MW of average power, which has significantly benefitted the community of Tomamae, however the area is known for its various airborne wildlife and birds of prey, including gulls, eagles, auklets, kites, and thrushes.  The results of the study showed that topography and vegetation had a tangible correlation towards the amount of bird deaths over those 17 months. In particular, coastal cliff regions accounted for a majority of the fatalities, producing roughly 20.1 bird deaths annually per MW of average power.  Furthermore, towers that were located in areas of woodland and bamboo forests saw much less deaths when compared to towers located in open plains. For example, a woodland turbine produced 0.32 deaths per year, while an open plains turbine produced 1 death per year.  Overall, the wind farm was calculated to kill 116.1 birds annually, which is fairly significant given the small size of the farm itself, a roughly 2000 m × 2000 m space. 
Smallwood conducted a study to determine a reasonable estimate for bird fatalities from all wind farms and turbines in the United States on an annual basis.  The study involved monitoring fatality reports at wind farms across certain regions of the country, adjusting that value based on the number of fatalities that go unreported, then establishing an estimator paired with three adjustment factors to determine a general value for the multiple of bird deaths/MW of average wind power.  The results indicated that Smallwood's estimates on bird fatalities came in at roughly 615,000 - 888,000 bats and 573,000 birds annually from a total of 51,370 MW of average wind power across United States as of 2013.  This estimate was nearly 20x larger than estimates from previous studies, indicating a severe miscalculation towards the effects of wind turbines on wildlife. Smallwood noted that there were significant discrepancies in terms of the fatality reporting at certain wind farms, as some deaths had not been calculated due to the method of reporting (human vs. dog retrieval systems).  Overall, this study shows the sheer magnitude of the problem, and the previous lack of proper estimates to accurately portray the effect these wind farms have on the birds and bats.
These two studies were different in location and magnitude, however both provided valuable insights towards the relationship between wind energy and the local wildlife. Although further studies are necessary, there is general consensus amongst the researching community that factors such as location, topography, and density of turbines has certain effects on the frequency of wildlife fatalities on these wind farms.  In order to prevent these deaths from increasing, it is in the best interest for all new wind projects and their developers to conduct preliminary studies to determine an optimal configuration of turbines to maximize energy output while minimizing future fatalities.
© Charles Skolds. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 J. Kellett, "The Environmental Impact of Wind Energy Developments," Town Plann. Rev. 61, 139 (1990).
 M. Kitano and S. Shiraki, "Estimation of Bird Fatalities at Wind Farms With Complex Topography and Vegetation in Hokkaido, Japan," Wildlife Soc. Bull. 37, 41 (2013).
 K. S. Smallwood, "Comparing Bird and Bat Fatality-Rate Estimates Among North American Wind-Energy Projects." Wildlife Soc. Bull. 37, 19 (2013).