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March 31, 2021

CORVALLIS, ORE. – Reduction in wildlife mortality rates is sometimes cited as a potential benefit to the replacement of older, smaller turbines by larger, next generation turbines. In contrast, others have expressed concern that newer, larger turbines may actually increase bird and bat deaths.

Two people kneeling to collect a carcass
Scientists collect carcasses at a wind energy facility to estimate total wildlife mortality at a site. (Public domain.)

A new USGS-led study suggests that the relative amount of energy produced by turbines in a given location, rather than simply their size, determines the rate of wildlife deaths. The study was published in the Journal of Applied Ecology on March 31.

Repowering is the replacement of smaller and tightly spaced turbines that each have a lower power capacity with fewer, larger, higher power-capacity turbines installed farther apart to generate similar or greater electrical energy output within the same area.

As capacity, size and the number of turbines have grown globally, so has the need for reliable information regarding bird and bat fatalities caused by collision with rotating turbine blades, as well as ways to lessen such adverse impacts on wildlife. In this and other research, USGS scientists are studying the effects of energy infrastructure on wildlife and are working to develop technical and management options that can reduce risks to wildlife.

“Facility and turbine location, as well as the amount of energy production, are likely stronger determinants of wildlife deaths than the size of turbines installed,” said Manuela Huso, a USGS research statistician and the lead author of the report. “Our study indicates that simply replacing older and smaller wind turbines with newer and larger machines generating the same amount of energy has little effect on the rate of wildlife mortality. Additional, carefully designed studies are needed, however, to confirm these results.”

Person with a dog on a leash near wind turbines
Dog-handler teams with high detection rates searched for carcasses to provide estimates of total wildlife mortality at a site. (Courtesy of Rogue Detection Teams)

The field data were collected from May 2018 to April 2019 at the San Gorgonio Pass Wind Resource Area north of Palm Springs, California. This area was specifically chosen for the study because it includes turbines of a wide range of sizes in a confined area within which weather, wind, and bird and bat movements are similar for all turbines.

This study is the first to incorporate turbine operations, not just turbine size and location, in comparing rates of wildlife mortality among turbines at wind energy facilities, said Huso.

Using the amount of energy produced as the metric by which to represent turbine operations is particularly relevant to repowering projects in which old turbines are decommissioned and replaced with fewer but larger modern turbines. Wildlife deaths remained relatively constant per each unit of energy produced by turbines under similar environmental conditions regardless of the turbines’ sizes.

Huso emphasized that these results do not suggest that the number of deaths per each unit of energy produced will be the same in different locations. Environmental conditions and the way birds and bats use airspace may vary widely among locations, geographic regions and sites.

The study was funded by the Bureau of Land Management (BLM). Authors of the study are from the USGS, BLM and Rogue Detection Teams.

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