The production of wind energy is responsible for a phenomenon that could cause an imbalance to biodiversity: the death of thousands of bats across the world. Global data suggest that they are the vertebrates with the most documented fatalities in wind farms. It is estimated that a total of 780,000 deaths occur each year in the USA, Germany, Canada, and the UK. For every megawatt (MW) of installed capacity in the USA and Central Europe, 6 and 7 bats die each year, respectively — in Latin America, the numbers range from 2 to 57 bats per MW per year.
These data, from international research, were brought together in an article in the journal BioScience, coauthored by researchers from Brazil and eight other countries. Published in April in the Forum section, which covers syntheses of knowledge about certain topics with an emphasis on conservation and management, the document discusses the interaction of these animals with the turbines and suggests measures for reducing this mortality, such as reducing the speed of the blades during times when the animals are most active. It also proposes uniformity in legislation across countries.
“In Brazil, where data are still scarce, we have an estimate restricted to one wind farm in Rio Grande do Norte, of two dead bats per MW per year,” says biologist Enrico Bernard, of the Federal University of Pernambuco (UFPE), coauthor of the article. The data, however, cannot be generalized to the entire country, as local conditions affect the number of deaths at each wind farm. The survey was the result of the PhD research of biologist Marília de Barros, defended in 2019 at UFPE under the supervision of Enrico Bernard. It is estimated that 160 bats die each year in this wind farm alone.
The bats die from colliding with the wind turbines or by barotrauma, internal hemorrhaging in the lungs caused by sudden pressure changes around the turbines. In the article, the researchers report declining populations in Central Europe for species with high risk of collision, such as the common noctule bat (Nyctalus noctula). “As a wind farm has an operational lifespan of 20 to 25 years, the cumulative impacts can lead to the local extinction of populations,” observes Bernard.
This type of energy is growing across the globe: in 2023, a further 117 gigawatts (GW) were installed, 50% more compared to 2022, according to the report “Global Wind Report 2024,” from the Global Wind Energy Council (GWEC). According to the Brazilian Association of Wind Energy (ABEEólica), Brazil has 11,000 wind turbines installed in over a thousand wind farms and 31 GW of capacity.
“This is called a green dilemma, in which the generation and the expansion of a renewable energy can cause impacts on biodiversity,” says Bernard. There are also problems with birds and insects that collide with the blades, and the impacts on people, including the discomfort caused by the noise of the turbines.
Enrico Bernard explains that there is no consensus about why the blades attract certain species of bats. The evidence, especially in countries with a temperate climate, indicates that insectivores are the most affected by collisions and barotrauma due to flying at higher altitudes. In Brazil, frugivores, which feed on fruits and spread seeds, are also affected. The animals also suffer from the loss of habitats due to deforestation for the creation of new wind farms, or stop visiting an area as a result of the operation of the turbines.
Bats of the Molossus NUB and Artibeus planirostris species were found dead in a wind farm in the city of João Câmara, in the state of Rio Grande do SulGaitan Carlos | Thibaud Aronson
To reduce the problem
The group suggests that countries adopt measures to mitigate the damages on three levels: local, operational, and regulatory. The first step would be to avoid building wind farms in ecologically important areas for bats and in biodiversity hotspots. These include stretches of migratory routes or close to caves known to be shelters for these animals, as well as the edges of forests and bodies of water. The recommendation is that the turbines remain at least 500 meters from such areas.
At the operational level, the researchers recommend that wind farms restrict operations during periods of high bat activity, adopting curtailment, reducing the speed of the blades during times and periods when the animals are more active. According to data cited in an article about wind farms in the Northern hemisphere, a 10% reduction in rotation speed at these times would avoid up to 80% of the deaths, with a 3% loss in production.
At the regulatory level, the group proposes global guidelines for the protection of these mammals in wind farms and stricter licensing that requires monitoring and public data on mortality.
“This has been a major issue in Brazil. Our main gap is the lack of information about mortality,” says Bernard. By email, ABEEólica informed Pesquisa FAPESP that these data are kept by the environmental licensing agencies. “They are not confidential, and are made public in accordance with each institution’s information policy,” informed the association. “It is also worth highlighting that many licensing agencies already provide information and studies on their websites. Anyone who requires information about an environmental process can access it.”
Bernard, however, reports that access is difficult. “The data from studies and environmental impact reports should be public. But the companies often do not publish them and getting them from the environmental agencies is a struggle,” says the researcher, who produced a technical study in 2019 with Barros analyzing the quality of licensing in 13 states, considering impacts on bats.
For electrical engineer Luiz Carlos Pereira da Silva, of the University of Campinas (UNICAMP), who did not participate in the studies, the international group’s warning reinforces the importance of establishing monitoring programs with accessible data after the concession of licenses. “Thus, it is possible to develop strategies for mitigation and operation that minimize the deaths of these animals,” says the coordinator of the São Paulo Center for Energy Transition Studies (CPTEN), one of the Science Centers for Development supported by FAPESP.
Ecologist Ludmilla Aguiar, of the University of Brasília (UnB), who also did not participate in the work, highlights the need to advance research into mortality and about the national bat fauna itself in order to adapt the suggested measures to the country’s reality. “In the Northern Hemisphere, they are more active in the summer. Here, they are active all year round,” she observes. She stresses that the problem goes beyond the environmental issue. “If thousands of them die in the turbines, it harms our biggest product, which is agriculture. They are predators of agricultural pests.” Aguiar led a study published in the journal PLOS ONE in October 2022, which estimated that insectivorous species could prevent the loss of US$391 million per corn harvest in Brazil.
Scientific articles
VOIGT, C. C. et. al. Towards solving the global green-green dilemma between wind energy production and bat conservation. BioScience. apr. 2024.
BARROS, M. A. S & BERNARD, E. “Licenciamento ambiental de parques eólicos no Brasil: Qualidade das diretrizes estaduais para avaliação de impacto sobre morcegos.” In: Artigos trabalhos técnicos. São Paulo: GWEC/Grupo Canalenergia/ABEEólica, Brazil Windpower. pp. 504–23. 2019.
AGUIAR, M. S. et al. Going out for dinner ‒ The consumption of agriculture pests by bats in urban areas. PLOS ONE. oct. 2021.
