CASPER, Wyo. — Wind turbines are sometimes cited as a risk to birds.
While about 140,000-500,000 birds die from collisions with turbines each year in the United States, those numbers are dwarfed by the amount of birds dying from a variety of other human-related factors.
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- 365-988 million birds die from crashing into windows of buildings each year
- 89-340 million birds die from collisions with vehicles each year
- 8-57 million birds die from collisions with electric utility lines each year
- 900,000 to 14 million migratory birds die from electrocutions on distribution lines each year
- 6.6 million birds die in collisions with communications towers each year
- 500,000 to 1 million birds are killed in oil pits or evaporation ponds each year
While wind turbine collisions may account for a relatively small number of bird deaths when compared with these other causes, that number is expected to increase.
“Renewable energy sources such as wind energy are increasingly being relied upon to help meet nationwide energy demands,” USFWS says. “The Department of Energy (DOE) has a stated goal of wind energy sources contributing 20 percent of the nation’s total energy need by 2030.”
“As wind energy capacity increases under the DOE’s mandate (a six-fold increase from current levels), statistical models predict that mean bird deaths resulting in collisions with turbines could reach 1.4 million birds/year.”
The placement of turbines plays a role in the impact of collisions with birds.
“The risk of a bird collision with a wind turbine is influenced based on facility location (including turbine placement), turbine design, and how birds move across the landscape,” USFWS says. “Available data indicate that some regions are higher risk than others.”
Data from different regions suggest that:
- 7.85 birds per turbine are killed each year in California
- 6.86 birds per turbine are killed each year in the American east
- 4.72 birds per turbine are killed each year in the American west
- 2.92 birds per turbine are killed each year in the Great Plains
Turbines near migratory routes or along rivers, ridgelines or near coastlines may increase the threat to birds due to their increased prevalence in such areas.
The behavior patterns of different birds also influences the risk posed by turbines.
“Birds in soaring flight are unable to maneuver well and may be unable to avoid the turbine if soaring within the rotor swept zone,” USFWS says. “Birds that move during the daytime fly at lower heights and may be at higher risk of flying into the rotor swept zone than birds flying at night.”
“Birds that have lower flight heights and can congregate near summits and steep slopes or open habitats (areas where turbine placement is common) while searching for food, increasing their risk of collision with turbines.”
More than 200 species of birds have been documented as dying from collisions with turbines.
“Passerines (i.e., songbirds) are most commonly reported, followed by raptors that hunt by day such as hawks, eagles and falcons,” USFWS says. “Although fatality rates for raptors may be lower compared to passerines, raptors are especially vulnerable to collisions due to their flight behaviors.”
“Given the life history traits of raptors (i.e., long-lived and low reproductive rates) their populations are more at risk of decline from the number of different sources of impacts that affect these species on a daily basis.”
Taller turbines may pose a greater risk to birds since “the blades reach higher into the average “flight zone” of nocturnal migrating birds.”
“Therefore, with the expected development of taller turbines, increased bird collisions are likely,” USFWS says. “Additionally, data suggest that bird collisions may increase with tall structures that are greater than 350 feet above ground level.”
Tower design is also a factor.
“Older style turbines were made with lattice towers, which compared to monopole designs have an increased risk of causing bird/turbine collisions,” USFWS adds.
While lighting turbines has been suggested as a means to prevent some collisions, “one study found no difference in bird impacts between lit and unlit turbines, suggesting that lighting may not be the driving factor behind bird/turbine collisions.”
“Reducing the quality of habitat and removing carrion may reduce the attraction of local individuals from the wind facility and lower exposure risk, but this may not reduce the risk to birds migrating during the day and night,” USFWS says. “Ensuring proper siting of wind facilities is the first step in minimizing bird/turbine collision risk.”
“The Service is exploring a standard, scientifically supported method for proper siting.”