Wind turbines should be built at least 12 miles away from Great Lakes shorelines in order to protect the stopover habitats of migrating birds, according to a new analysis of flocks picked up on weather radar systems.
“This is much farther than has been considered before when making recommendations about siting wind turbines to avoid such bird concentrations,” says study team member Jeff Buler, a wildlife ecologist at the University of Delaware in Newark. Currently, the U.S. Fish and Wildlife Service suggests an exclusion zone of 3 miles, while the Nature Conservancy recommends 5 miles.
“The fine granularity and broad extent of weather surveillance radar observations made this discovery possible,” Buler says.
Buler and his collaborators analyzed data from seven weather radar stations collected over four years during the spring (early April through mid-June) and autumn (mid-August through end of October) migration seasons – 4,256 nights’ worth of radar data overall.
The Great Lakes region of the United States is “is a globally important bird area with significant current wind development that is projected to continue,” says study team member Emily Cohen, an ecologist at the University of Maryland Center for Environmental Science. Millions of migratory birds pass through the region every year.
Migrating birds tend to fly at night, and mostly stay far above wind turbines. But when they land to rest and refuel or take off to resume their migration, they pass through altitudes where they could collide with a turbine or its rotating blades, known as the rotor-swept zone. Wind energy installations can also destroy stopover habitat, and their presence nearby can alter birds’ behavior.
Nearly one-quarter of the migrating birds picked up on the seven radars stopped to rest somewhere along the shorelines of the Great Lakes, and one-third passed through the rotor-swept zone somewhere in the region, the researchers report in the journal Conservation Letters.
The locations where birds take off and land are both predictable and patchy, opening up the possibility of protecting birds by keeping wind turbines away from their favorite stopover spots. The percentage of birds both stopping over and passing through the rotor-swept zone is highest in northern Michigan and lowest in the southern part of the Great Lakes region. The researchers also identified smaller hotspots of potential risk throughout the region.
The risk to birds from wind turbines varies seasonally – for example, migrants are especially concentrated along the southern shoreline of Lake Michigan in spring but the northeastern shoreline in autumn. The risk also varies by time of day, with the greatest proportion of birds passing through the rotor-swept zone just before sunrise. These findings suggest that operators could further reduce the risk to migrating birds by turning off turbines at dawn and dusk, especially at times of peak migration.
Building wind turbines at least 12 miles from Great Lakes shorelines would keep them out of 50% of stopover habitat in the Great Lakes region. The current 3-mile and 5-mile thresholds capture only 8% and 19% of stopover habitat, respectively.
Although climate change may alter wind and migration patterns somewhat, “the general pattern of land birds concentrating along the edges of large water bodies like the Great Lakes or along ocean coastlines seems likely to remain robust,” says Buler, as will the dawn and dusk timing of landing and takeoff. So the study’s findings are likely to remain relevant over time.
And its methods are applicable to other areas as well. Another study by many of the same researchers found that roughly 50% of migrating birds that pass over the U.S. Gulf of Mexico coastline stop to rest and refuel there. “The good news here is that weather radar data are standardized, collected nearly continuously, and are archived and available, making data-driven bird-friendly wind development possible across much of the U.S.,” Cohen says.
Source: Cohen E.B. et al. “Using weather radar to help minimize wind energy impacts on nocturnally migrating birds.” Conservation Letters 2022.
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