AVIAN AND BAT MORTALITY
ENVIRONMENTAL AND WILDLIFE IMPACT
LOSS OF FARMLAND
As an emerging industry, questions and concerns often arise surrounding proposed and operating wind energy projects.
This information is designed to give answers to common concerns and frequently asked questions. Facts and figures from
independent sources were used to support the information.
AVIAN AND BAT MORTALITY
Proper studies and precautions minimize the impact wind energy projects have on birds and other wildlife.
It is estimated that for every 10,000 birds killed by all human activity, less than one death is caused by wind turbines. In fact, a study by
the National Research Council (NRC 2007) concluded that current wind energy generation is responsible for 0.003% of human-caused
avian mortality. The numbers are expected to stay relatively low as wind energy starts playing a more significant role in total energy
production. However, it is important that proper precautions continue to be taken in siting and design and that sitespecific environmental
examinations be conducted to assess future impacts. In the 1980’s, an extensive number of unforeseen raptor deaths occurred in
Altamont Pass, California, due to poor siting, lack of pre-construction studies and the use of wind turbine technology that did not
incorporate the modern designs of today.
The Union of Concerned Scientists reported in 2004 that bird fatalities most often occur at older turbines that have fast-moving blades
and lattice tower structures that proved to be an attractive nesting and perching spot for birds. The study states, “Fortunately, significant
progress has been made in reducing bird fatalities. Newer turbines typically feature slower-moving blades and tubular steel towers that
reduce opportunities for perching and nesting. These turbines are also much larger than earlier models, allowing wind developers to
use fewer, more dispersed turbines at a given site. Developers are also more conscious now of how their choice of site for a new wind
farm can minimize its impact on local and migratory bird populations. Even if wind power supplied all of the United States’ energy needs,
wind turbines would constitute only a small fraction of the estimated 200 million to 500 million annual bird fatalities attributable to human
activity (e.g., vehicles, buildings and windows, power lines, communication towers, airplanes, house cats).” The National Audubon
Society has also issued a statement supporting properly sited wind power as a clean energy source that reduces the threat of global
In the recent past, much focus has been geared toward bat mortality at wind energy project sites. Prior to 2003, bat fatalities at wind
projects were thought to generally be low. However, in 2003 post-construction avian studies at a wind project in West Virginia discovered
bat fatalities in numbers much larger than previously known. Since then, bat fatalities have been documented at higher than expected
rates at many other locations across the US. In response to the issue, AWEA, Bat Conservation International, the U.S. Fish and Wildlife
Services and the U.S. Department of Energy’s National Renewable Energy Laboratory founded a new organization, the Bats & Wind
Energy Cooperative (BWEC), in late 2003. In addition to the founding organizations, BWEC is also funded by a diversity of partners
who are focused on finding good site screening tools and testing minimization and mitigation measures that can reduce a wind project’s
impact to bats.
Despite the minimal impact wind development has on bird and bat populations in most areas, the industry takes the potential impact
seriously. Special initiatives and preconstruction environmental surveys, including avian and bat studies, are now common practice
throughout the industry.
i. The Union of Concerned Scientists (UCS) is the leading science-based nonprofit working for a healthy environment and a safer world.
UCS combines independent scientific research and citizen action to develop innovative, practical solutions and to secure responsible
changes in government policy, corporate practices and consumer choices.
ii. The National Audubon Society is an environmental nonprofit. Audubon’s mission is to conserve and restore natural ecosystems,
focusing on birds and other wildlife and their habitats for the benefit of humanity and the earth’s biological diversity.