Wind turbines have long garnered scrutiny for killing birds that fly into their spinning blades or tall towers. Much of the data about bird deaths at wind facilities in the United States comes from studies published in 2013 and 2014. Those studies gave a wide range for the number of birds that die in wind turbine collisions each year: from 140,000 up to 679,000.1 The numbers are likely to be higher today, because many more wind farms have been built in the past decade.2
Those numbers are not insignificant, but they represent a tiny fraction of the birds killed annually in other ways, like flying into buildings or caught by prowling house cats, which past studies have estimated kill up to 988 million3 and 4 billion4 birds each year, respectively. Other studies have shown that many more birds—between 12 and 64 million each year—are killed in the U.S. by power lines, which connect wind and other types of energy facilities to people who use the electricity.5
Other sources of electricity are also more lethal for birds than wind energy. A 2012 study found that wind projects kill 0.269 birds per gigawatt-hour of electricity produced, compared to 5.18 birds killed per gigawatt-hour of electricity from fossil fuel projects.6 That’s in part due to collisions with equipment (wind turbines aren’t the only energy infrastructure birds can fly into), but mostly because of the environmental impact of fossil fuels. Coal mining has torn down forests and destroyed habitat, and burning coal produces air pollution tied to acid rain and mercury contamination, which scientists have linked to bird health impacts like birth defects. But when it comes to bird deaths, the most significant impact from fossil fuels is their contribution to climate change, which scientists expect will be extremely dangerous for birds. The National Audubon Society estimates that about two-thirds of bird species in North America are at increased risk of extinction due to rising temperatures and changes to the habitat where they live.7
“When assessing electricity generation technologies, it’s important to evaluate against baseline generation alternatives, because electricity generation is a requirement of modern society,” says Michael Howland, MIT professor of civil and environmental engineering. “Fossil fuels contribute to climate change, increased air pollution, and negative impacts on human and animal health, including birds, among other issues. Wind energy is an electricity generation technology that significantly reduces such environmental and health impacts.”
Still, scientists and conservationists are actively working to minimize bird interactions at wind facilities. “Environmental impact studies” are conducted before the construction of large infrastructure projects, including wind farms, and are meant to ensure projects are not sited in locations that pose a risk to protected species. Researchers are still trying to understand all of the reasons why birds may crash into turbines, such as poor visibility or migration patterns.8 Some conservation biologists are studying how specific species and migration routes are affected by wind facilities, and if wind farms built in certain places may have an outsized impact on vulnerable bird populations.
There are also ways to build safer wind farms for birds. Before construction, wind companies survey sites, and can place fewer turbines in areas most important for habitat, or leave those areas alone entirely. Scientists have found that painting one blade of a turbine black, which can increase visibility, can reduce bird fatalities by more than 70 percent.9 And some wind companies are experimenting with using artificial intelligence to sense a bird’s approach, powering turbines down to avoid collisions.10
Thank you to Julie Grant of Rowland Heights, California, for the question. You can submit your own question to Ask MIT Climate here.
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Numerous studies have demonstrated that both humans and wildlife will suffer greatly as a result of climate change. The development of renewable energy is a vital part of the shift away from fossil fuels, which will clean our air and reverse the effects of climate change. Regretfully, we have also discovered that the development of wind energy has a significant detrimental effect on birds.
But just how many birds are killed by wind turbines?
There are many different responses to this question that can be found through a Google search, with the difference between the smallest and largest estimates being almost five times.
Actually, a lot has happened in the wind energy industry since these estimates were last updated, which was quite some time ago. Therefore, we believed it was time to carefully review the data and determine what a current estimate might entail.
The best estimates of the number of birds killed by wind turbines in the U.S. each year are based on a trio of studies published in 2013 and 2014, all reporting on data from 2012. Each study was unique in its methods, resulting in varying estimates. (There is actually a fourth paper just to compare their methods.) The results from these studies are provided in the table below.
| Study | Year Published | Average Bird Fatalities/Year | Minimum – Maximum/Year |
| Loss and others | 2013 | 234,000 | 140,000 – 328,000 |
| Smallwood | 2013 | 573,093 | 467,097 – 679,089 |
| Erickson and others | 2014 | 291,000 | 214,000 – 368,000 |
Instead of delving too far into the hypothetical to determine which study is the most accurate, let’s take the mean of these studies’ findings. This provides us with an estimate of the number of birds killed by wind turbines in the United S. in 2012.
Its important to consider that wind energy capacity has grown considerably since then. The study by Loss and others reported that there were 44,577 turbines in operation in 2012, while the U.S. Wind Turbine Database indicates that there are 65,548 today — an increase of 47 percent. Adjusting for this industry growth, we can project that approximately 538,000 wind turbine-caused bird deaths occur in the U.S. each year.
However, projecting mortality based on energy produced is more frequently used because it accounts for the size of turbines in addition to their numbers. The American Wind Energy Association reports that there were 60,067 megawatts (MW) of wind energy capacity in the U.S. in 2012, versus 111,808 as of this writing in 2021 — an 86-percent increase. Taking this change into account, it can be projected that approximately 681,000 birds are currently killed by wind turbines in the U.S. each year.
These estimates probably don’t reflect the full scope of the issue because a large number of bird deaths go unreported by humans.
Consider that small songbirds are the most abundant birds in the U.S., and are the most frequently killed by turbines. A study published in March 2020 found that dogs located 1.6 and 2.7 times as many small bird fatalities as human monitors did at two wind sites in California. This was true even after attempting to correct for searcher detection error, which is a standard practice for such studies.
The Erickson study reported that 62. Small birds made up 5% of the birds in their data set. Taking 62. 5% of the 681,000 annual mortality estimate that was computed earlier, and modifying this using the 1 6- and 2. seven-fold multipliers from the study on dog searches (plus the additional 37 5 percent of birds returning in), which adds up to 936,000 and 1 4 million birds according to data from the two locations. Averaging the two, this would suggest that 1. In the United States, wind turbines kill 17 million birds annually.
Apart from the previously mentioned bird fatalities, wind power projects also result in significant indirect effects that need to be taken into account.
For instance, a lot of wind farms need to build new powerlines since they are situated far from the current power grid, which is another reason why birds die.
In a 2014 study, researchers estimated that 25.5 million birds are killed each year due to collisions with powerlines, and another 5.6 million are killed by electrocutions. Therefore, powerlines built exclusively to connect new wind facilities to the existing energy grid result in additional bird mortalities that should be factored in to the total toll in birds associated with wind energy development.
Wind facilities also require relatively large areas of land. Facility development can fragment or otherwise alter habitat in ways that make it unsuitable for species that have historically been present. For example, a study at wind facilities in the Dakotas found displacement effects for seven of nine grassland bird species after one year. While these effects have been documented in various studies, they have yet to be broadly quantified.
When the aforementioned information is taken into account, it is evident that current estimates of the cost of wind energy development on birds are limited in scope and do not fully account for the industry’s effects.
Because the estimates above are based on studies that were derived from an incomplete data set, it should be noted that they are not perfect.
Although the majority of wind farms must carry out bird surveys in order to provide information for project planning and post-construction studies on bird mortality, these facilities are regrettably not always required to share the results of their surveys, and many businesses keep the data confidential. Public access to these data would improve understanding of bird mortality and allow for more customized conservation recommendations.
Equally important, we need to take into account the species that wind turbines are negatively affecting. Certain species are more vulnerable to wind turbine collisions than others, and because they reproduce more slowly, the losses they sustain may have a greater impact on their populations. This includes some of our rarest and most iconic species, like Marbled Murrelets and California Condors, which are in danger of colliding with wind turbines. Others, like Whooping Cranes, are losing their natural habitat due to the development of wind energy.
As previously mentioned, our estimates show that the annual loss of birds to the United S. at least 500,000 wind turbines; a similarly conservative estimate would place that figure closer to 700,000 birds. One could argue that the figure is higher than one million. And for all the previously mentioned reasons, these are probably all underestimates.
Whatever the details, given the numerous other threats to birds on the landscape and the significant declines in bird populations that we have already witnessed, this is far too many.
The answer to this paradox is bird-smart wind energy. How can we combat climate change while installing more wind turbines and endangering birds at the same time? The first steps in developing smart wind energy are gathering quality data and choosing a location that keeps birds out of high-risk areas. Then, feasible actions can be taken to further reduce risks, and effects must always be countered by effective on-the-ground mitigation strategies.
For more than ten years, American Bird Conservancy has worked to reduce the effects that wind energy development has on birds. We can realize the benefits of renewable energy while safeguarding our vulnerable bird populations if we make sure that this development is done correctly.
| Joel Merriman is American Bird Conservancys Bird-Smart Wind Energy Campaign Director. |
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