Environment | Wind Turbines



Bird and bat mortality facts by wind turbines

Wind is one of the cleanest means of harnessing energy. Unlike traditional energy sources, wind power is free of pollutants such as particulate matter, methane, mercury, sulfur dioxide, and nitrogen oxides. There is no fuel required for mining or drilling, billions of gallons of water are not consumed during operation, and small amounts of waste are produced. As the global demand for sustainable energy increases, thousands of wind turbines are installed every year.

Unfortunately, then, wind energy has its own dark side: Thousands of birds and bats are killed each year by wind turbines. Causes of death include collision, pressure trauma, and internal injuries due to exposure to rapid pressure changes near the posterior edges of the moving blade.

The US Fish and Wildlife Service estimates that between 140,000 and 500,000 bird deaths occur on wind farms each year. The most important threat is large, threatened bird species of high conservation value such as golden eagles, bald eagles, burrowing owls, red-tailed hawks, Swanson hawks, peregrine falcons, prairie hawks, American hawks and white-tailed kites. And because large birds have much lower reproduction rates than young birds (golden eagles, for example, have one or two chicks per brood less than once a year), their death has a much greater impact on the total number of species.

Wind turbines have also been found to be one of the main causes of mass bats deaths, with some studies indicating that deaths reach 888,000 bats annually.

« Unprecedented numbers of migratory bats were found dead under wind turbines on an industrial scale during late summer and fall in both North America and Europe, » says Paul Crean, a research biologist at the US Geological Survey. « There are no other well-documented threats to migratory tree bat populations that are causing mortality of a similar magnitude to those observed in wind turbines. »

Paul Crean

The importance of saving bats

Bats may not be a favorite of many people, but they play an important role in the planet’s ecosystems. Not only do aerial mammals consume hordes of pest insects, but they also play an effective role in pollinating flowers and spreading seeds to replenish rainforests.

In North America, tree bats make up about 75 percent of the bat species affected by turbines, and floating bats make up half of all deaths. According to the journal Biological Conservation, the floating bat population could be at risk of extinction due to deaths from wind turbines. Like large birds, bats are long-lived mammals with low reproductive capacity, and require a high percentage of adult survival to maintain a population. And widespread bat deaths in wind turbines (literally) could reduce the number of bats by up to 90 percent in the next 50 years.

Unlike previous years, wind energy companies are now responsible for completing environmental impact assessments(EIAs) prior to installing wind turbines in the region. Bird migration routes are avoided, and vegetation surveys are conducted under the turbines to ensure that there are no preferred food sources for migratory birds. In Spain, some wind energy companies shut down wind farms when large numbers of migratory birds approached.

A 2019 study published in the Journal of Environmental Management describes mitigation measures that involve plowing the topsoil around the base of the wind turbines making the area less attractive to beams due to the resulting reduction of prey around the turbines. The results were a 75-100 percent reduction in collisions over two years.

More recently, Norwegian scientists discovered that coating one of the three blades on a wind turbine black reduces bird deaths by 72 percent.

The Norwegian Institute for Nature Research conducted this research over a decade from 2006 to 2016 at the Smøla wind farm on a bird-rich island off the western coast of Norway. In 2013, there were four single-blade turbines painted black, and bird deaths were recorded in the years before and after the paint job. The resulting data showed a significant reduction in the annual mortality rate for the coated turbines relative to the control (i.e., uncoated) turbines.

read : Why wind turbines are white?

The scientists behind the study have a theory as to why birds are so vulnerable to flight to the rotating turbine blades and why a single black blade helps them perceive wind turbines as an obstacle.

“For humans, birds have a narrow microscope [using both eyes to focus on a single object] the frontal field of view and potentially monoculars [using each eye separately]. Facing each other of their heads] to detect predators, birds [of the same type] and prey. ”Within the supposed open airspace, birds may not always see obstacles in front of them, which increases the risk of collision. To reduce susceptibility to collision, providing « passive » visual cues may enhance the visibility of rotor blades, allowing birds to take evasive action in a timely manner. « 

In other words, birds may perceive the rotating white blades to be a « moving space » rather than as a moving object like the camouflaging effect that humans see when they rapidly wave their hand before their eyes. Once the blade is painted black, the birds correctly distinguish movement patterns as a moving object.

In order to develop practical solutions to reduce bat deaths around wind turbines, it is necessary to understand the causes of collisions. While aggregation prevails during migration as the most common source of mortality, several studies indicate that bats may be attracted to turbines out of curiosity, misunderstanding, or as potential opportunities to feed, live and mate.

read also Wind Turbines kill Birds and Bat

A Deterrent system could save bats

Promisingly, then, researchers at Texas State University and Bat Conservation International have found an innovative solution to dissuading bats from entering wind turbine airspace: a bat deterrent system that disrupts the bats’ ultrasound echolocation capabilities. The bats make a high-frequency call that reflects on things, including their prey. They rely on echo to determine the distance and direction of their prey, enabling them to move around and search for food in the dark.

Bat deterrent

The bat deterrent system, manufactured by NRG Systems, uses an array of amplifiers to produce an ultrasonic sound field at 20-50kHz, the same range of natural echolocation frequencies as bats. This interferes with their ability to receive and interpret their echolocation sounds and creates an airspace that is difficult to navigate, forcing the bats to surrender and leave the area. Data collected over two years show that NRG bat deterrent technology reduced bat mortality by 54 percent, with particularly positive results for Brazilian freestyle bats and bats.

Interestingly, the idea is based on echolocation in nature. Some tiger butterflies protect themselves from becoming bat food by emitting clicks that interfere with echolocation of bats.

The technology won ‘t harm the bats

And if environmentalists are concerned, the technology will also not push bats away from their natural habitats. The bat deterrence system only covers the turbine sweep area of ​​the rotor, so bats feeding below this level are completely unaffected. Moreover, there is no risk of getting used to as the speakers lose their effectiveness as bats get used to them (as the idea of ​​a bird sitting on a scarecrow). Rather than simply disturbing or frightening bats, technology undermines the echolocation capabilities that bats rely on most.

« One of the challenges is the physics of sound propagation at high frequencies, » says Aaron Corcoran, associate professor at Wake Forest University. Ultrasound weakens very quickly in air.

Aaron Corcoran,

The lower frequencies are more likely to dissipate than the higher ones, which leads to a species-specific response as the technology works best to protect bats that locate the echo at the lower end of the ultrasound spectrum.

Bat-repelling whistling wind turbines

Another innovative approach to preventing bat death in wind turbines involves the use of 3D-printed echolocation whistles similar to a bat’s throat. These lightweight whistles can be installed on the turbine blades to passively generate ultrasonic sounds as warning signals from bats without the need for a power source.

By making a noise that bats can easily recognize at distances of more than 100 meters, the whistles give the bats more time to change their flight path and avoid collision with the turbine rotor blades. The project is led by researchers at Texas A&M University and the University of Massachusetts Amherst and is funded in part by the US Department of Energy in an effort to protect wildlife on wind farms.

Without exaggeration and fallacies, the effect of wind energy on bird numbers is relatively small.

If we look at the bigger picture, the effect of wind energy on bird numbers is relatively small when compared to other bird deaths associated with humans. Several studies may show that much more bird deaths are caused by collisions with buildings (676 million), vehicles (214 million), and power lines (32 million) in the United States. (It should be borne in mind, however, that birds killed by wind turbines have historically had a higher protection value than birds killed by non-wind sources.)

Even with its relatively low impacts, the wind industry holds itself to a higher level and does more to mitigate wildlife damage than any other energy industry. Wind energy developers continually assess the risks to birds prior to identifying project sites, and adjusting the wind farm design, turbine site, and project operations to minimize potential harm. The wind industry follows onshore wind power guidelines from the U.S. Fish and Wildlife Service and as a result, more than 90 percent of U.S. wind farms have no vulture deaths.

In 2008, the US wind industry collaborated with national-level conservation organizations such as the National Audubon Society and the National Wildlife Federation to establish the American Wind and Wildlife Institute, which addresses wind and wildlife concerns. The organization has published briefs on bat protection, for example with proposals to implement downsizing (deliberate stopping of turbine blades) when wind speeds are low in order to reduce bat deaths by 50 percent.

In the end, it is climate change that is causing the greatest threat to wildlife. According to the United Nations, climate change may contribute to the extinction of 20-30 percent of all species by 2030. Renewable wind energy can play a major role in replacing energy sources that contribute to high carbon emissions, and it has been shown to outweigh its impact on birds and bats. .

read also: A major risk of electrical lines on birds

« To say that wind energy can only be environmentally friendly if there are no effects like saying that medicine can only be effective if it has no side effects, » says John Anderson, director of positioning policy at the American Wind Energy Association. « At some point, we need to put the benefits and risks into context. »

John Anderson

Why Should You Care?

Bats play a critical role in the environment. They are the number-one predator of night-flying insects. Their value to U.S. agriculture has been estimated in a recent study at $23 billion annually.

How You Can Help

You can help save bats by donating to The Nature Conservancy in Tennessee to support white-nose syndrome research for an effective treatment.

Help Save Bats

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