Bats and Wind Energy Development

Bat fatalities at wind energy facilities are a growing concern, particularly since bats have low reproductive rates and populations are slow to recover from long-term, large-scale impacts. Although bat carcasses have been reported underneath wind turbines since the early 1970’s, it was nearly 30 years before turbine-related bat fatalities received much attention. Over the past decade, our understanding of how and why bats interact with wind turbines has increased, with most data coming from the United States, Canada, and Europe. Yet, many questions remain unanswered even in these well-studied regions, and almost no data are available from the rest of the world.

It is possible to sustainably generate electricity from wind resources, but resolving concerns over bat mortalities requires engagement from all stakeholders involved including the wind industry, government agencies and the conservation community. The Bats and Wind Energy Cooperative (BWEC), which began in 2004, is an example of diverse organizations working together to identify priorities, conduct research, provide credible recommendations to reduce risk to bats, and support long-term responsible wind energy development. One of the BWEC’s strengths is its ability to facilitate open dialogue among stakeholders. Beginning with this post, we would like to stimulate conversations among the international community on this issue.

In the United States and Canada, 23 species have had fatal interactions with wind turbines; nearly 78% of fatalities come from 3 species which are commonly referred to as migratory tree bats. However, other species including the Brazilian free-tailed bat and little brown bat can account for a large proportion of fatalities at some sites. At least 27 species across Europe have been reported, with migratory and non-migratory species frequently killed in northern and southern Europe, respectively. Species in the genera Pipistrellus and Nyctalus are the most commonly killed bats across the continent.

We know very little about the species composition of fatalities elsewhere in the world. This may be due in part to the limited wind energy development in certain regions such as Africa. China, however, is the world leader in installed wind energy capacity and has yet to provide data on turbine-related bat fatalities. Few studies have been conducted in the tropics; recent reports from Latin America suggest that species not represented in temperate regions are affected and the species, genera, and family diversity of fatalities can be high.

Our lack of understanding of the extent and magnitude of this issue is related to the paucity of bat population and behavior data, and the dearth of publicly available studies. The former is a result of the cryptic nature of bats and the difficulty in studying small, nocturnal, flying animals. The latter is a human-induced problem caused by a lack of consistency in monitoring protocols and fatality estimation, few long-term and broad-scale studies, and access to data. These deficiencies make it difficult to quantify the potential population-level impacts of wind turbines on bats. Unfortunately, these challenges are prevalent across the globe and are even experienced in countries with a long history of studying the issue (e.g., the United States and Europe). The behavior and mortality of bats at wind facilities are among the best studied sources of anthropogenic impact on bats.

There are no easy answers, but there are steps we can take to better understand the impacts of wind turbines on bats, and develop and implement ecologically sound and economically feasible solutions:

  1.  Guidelines for monitoring are necessary to accurately and precisely quantify the impact of wind turbines on bats and determine the potential risk at a site or in a region. Consistent methodologies also allow for greater comparability among wind energy facilities.
  2. Disseminating results from studies is critical. The lack of available data inhibits our understanding of the issue that would benefit all stakeholders. Initiatives such as IEA Wind’s Task 34 and tools such as WREN Hub and Tethys can play an especially important role in disseminating integral information and research to the international wind energy community. WREN and Tethys are implemented by Pacific Northwest National Laboratory (PNNL), the National Renewable Energy Laboratory (NREL), and the US Department of Energy (DOE).
  3. Finally, strategies to reduce the impact to bats should be anticipated and implemented when necessary. For example, feathering turbine blades (i.e., adjusting the angle of the blade parallel to the wind or turning the nacelle out of the wind to slow blade rotation) below the manufacturer’s cut-in speed should be considered as a viable minimization approach for wind energy facilities in order to reduce bat fatalities. Feathering turbine blades and other strategies may also be considered as potential best management practices for all facilities moving forward. This action has been proven to reduce bat fatalities and has little to no impact on energy production.

Because the complexity of bats and wind turbine interactions cannot be described within a few paragraphs, BWEC would like to invite you to join the online forum below on this Tethys page. We welcome your contributions, reflecting your experience and knowledge so we can all benefit from lessons learned and work together to protect bats and generate renewable energy.

Cris Hein, Ph.D.
Director, Bats and Wind Energy for Bat Conservation International
Program Coordinator for the Bats and Wind Energy Cooperative



On 3 September 2015, the American Wind Energy Association (AWEA) announced the first industry-wide best management practice for wildlife, aimed at reducing bat fatalities. The new protocol is voluntary, but has been endorsed by 17 wind industry companies operating the vast majority of facilities across the U.S. It also has been hailed by Bat Conservation International and other conservation organizations.

The management practice involves limiting the rotation of turbine blades during the fall bat migration under low wind speed conditions, when little to no electricity is generated. This operational change, often called feathering, stems from more than a decade of collaborative research, including work by the Bats and Wind Energy Cooperative, an alliance of industry, academia, state and federal agencies, and the conservation community.

When monitoring bats at proposed and operational wind energy facilities first began, it became clear that higher bat activity and fatality rates were negatively related to wind speed. Using this information, researchers from Europe, Canada, and the United States demonstrated significant reductions in bat fatalities at turbines that were feathered below the manufacturer’s cut-in speed or below higher cut-in speeds. Often called operational minimization, this strategy is the only proven method of reducing bat fatalities at wind turbines.

AWEA’s announcement represents a significant step toward bat conservation in the U.S., with the potential of reducing thousands of wind turbine-caused bat fatalities. Additional research is needed to determine how effective this strategy is in other parts of the world with different assemblages of bat species. Moreover, optimizing this practice and developing alternative impact reduction strategies will ensure bats are protected and promote the responsible development of wind energy.


Questions for the Community:

  1. What specific topics are of interest to the community? (i.e., what should we focus on with subsequent posts?)

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Submitted by Ian M Davies on Fri, 07/24/2015 - 22:28


There are some suggestions that effects on bats can occur at offshore wind farms, affecting bats on migration across small to moderate stretches of sea. Do you think these are actually or potentially significant risks to the populations concerned?

There is growing evidence of bats migrating offshore, both from Europe and N. America. There are several published articles documenting these movements. Whether it has significant impacts on populations, likely depends on the species of bat and the location of the facility/facilities. The difficulty is in assessing the impact as there is no known way to document fatalities offshore as there is on land. Although there are several groups looking into integrated detection systems using cameras/acoustics/strike indicators, etc. These show promise but will need to be calibrated on land. I encourage anyone else who knows more about bats/offshore wind energy to chime in!

Submitted by Mike Johnson on Tue, 07/28/2015 - 04:09


Regarding the use of best management practices (BMP), I'm curious if there are any data on the effects of lighting at wind turbines and bat mortality. My town has had two, land-based wind turbines in operation for about 5 years, and they were reporting about 12 bat mortalities/year for the first 2 years. They turned off the spotlights that were directed upwards and towards the turbine towers and to my knowledge have not had any reported bat mortalities since. The hypothesis was the lights were attracting flying insects. Are you aware of any data on this phenomenon?

It depends on the type of lighting. There has been no evidence that turbines with FAA lights have a significantly higher impact on fatality compared to unlit turbines. In fact, a recent publication by Bennett and Hale showed that red FAA lights may have fewer fatalities of red bats than unlit turbines. However, this is a different type of lighting than what you mention. Lights emanating from the ground have frequently caused problems for both birds and bats. This type of lighting can attract insects, which then attract bats. I believe there are publication of bats foraging around streetlights. I am not aware of any publication that documents higher fatality of bats at turbines with ground-based lighting. It is highly recommended for both bats and birds that lights at the base of turbines or at buildings near turbines reduce or eliminate any permanent lighting and only use hooded lights that are motion sensitive and will turn off after a short period of time. There are BMPs in the USFWS Land-based Wind Energy Guidelines for the proper use of lighting. Anyone with additional insights, please weigh in!