Altamont Pass in California is one of the world’s largest wind farms — and most notorious among bird lovers. Much of the anxiety around wind turbines and raptor collisions comes from the large number of eagle fatalities reported from this single cluster of wind farms east of the Bay Area.
In 2005, the wind farms’ operator sought to reduce bird deaths by replacing 126 turbines with 26 larger ones that rotated more slowly and that were spaced farther apart. Over the next few years, bird collisions with the newer turbines were 66 percent lower compared to the older turbines.
But there was an unexpected side effect: bat fatalities were 800 percent higher on the newer, larger turbines.
When it comes to preventing wildlife fatalities at wind farms, scientists are learning that bats are indeed a whole different animal than large birds.
Strategies that have worked for minimizing bird collisions have been ineffective, or in some cases counterproductive, for bats, which play a critical role in plants pollination and provide billions of dollars worth of free pest control to the nation’s agricultural industry.
A fatal attraction?
Laura Ellison is an ecologist with the U.S. Geological Survey in Fort Collins, Colorado, who has spent the last 20 years studying bats and other small mammals. Last month she presented on the bat and wind farm issue at the North America Congress for Conservation Biology.
“The newer, larger turbines seem to be worse for bats,” Ellison said in an interview in late July. Researchers are just scratching the surface in understanding why that is.
A few theories exist for why bats and blade collisions occur. One is that bats just happen to be in the wrong place at the wrong time, but there’s also evidence that bats, particularly tree bats, are actually attracted to wind turbines.
“Video recordings are showing that bats are just going towards these turbines. They see this tall structure on the landscape, and they’re very curious,” Ellison said.
They might be scoping turbines out as potential roosting sites, or maybe as places to meet a mate. Another hypothesis speculates that insects gather more densely around turbines.
The attraction theories might explain why siting decisions haven’t seemed to have worked in preventing bat collisions. With birds, building farms away from prime habitat or migration flyways is promoted as the best way to prevent collisions, but that hasn’t worked for bats.
“There doesn’t really seem to be a pattern,” Ellison said. Wind farms have been built in areas with little bat activity, but after construction they experience scores of bat deaths.
More research needs to be done on siting issues, she said.