Wind turbines kill a lot of birds, particularly eagles and other raptors. The exact number is unknown, because many of the world’s wind farms don’t monitor bird deaths. One mitigation idea to reduce these numbers—and assuage a political argument against wind turbines—is gaining traction: Paint one turbine blade black. Ecologist Roel May spoke with IEEE Spectrum about his 11-year study to reduce raptor deaths, and his surprise at the lukewarm reactions from wind-turbine engineers.
Roel May
Roel May is a senior research scientist focusing on renewable energy impacts and mitigation at the Norwegian Institute for Nature Research (NINA) in Trondheim, Norway.
How bad are wind turbines for birds?
Roel May: It depends a lot on where you put the turbines, and whether there’s breeding or foraging areas nearby, and the species of birds. If you put wind turbines smack in the middle of a vulnerable population, the effect can be quite large. That’s what happened in Norway on the island of Smøla, which is a hot spot for white-tailed eagles. That’s where we did our study.
Why are eagles susceptible to wind turbines?
May: Raptor species like eagles are very good at flying, but they don’t look straight ahead; they look down at the ground for prey. They like to use updrafts to soar, but updrafts are common near ridges where wind conditions are good for turbines. So that’s a bad combination.
Does the wind-turbine type make a difference?
May: Larger turbines kill more birds because their blades take up more area. But where wind turbines are smaller, there’s often more of them, so those wind farms may end up killing more birds than farms with fewer, larger turbines, at least onshore. Offshore wind farms are harder to study: You can’t count the exact number of birds that die because you can’t find them; they fall into the sea and they’re gone. Some researchers are trying to record collisions with bird radarcameras, and other systems.
You found that painting one blade black resulted in a 70 percent decline in bird deaths. Should all wind farms be doing this?
May: Our study is something that should be repeated in other places because there are likely site-specific and species-specific effects. A group in the Netherlands painted blades and hasn’t seen a clear effect. So we need more studies. There’s one study going in South Africa where they painted a blade redand some others that arestarting in WyomingItaly, and Spain. The United Kingdom is planninga pilot project for offshore turbines. But these studies are hard to do because the operator has to get exemptions from regulations to paint the blades and hire certified painters who can rappel up and down. And it takes a lot of time. We collected data on eagles in Smøla for seven years before the blades were painted. After we painted, we spent four more years studying the effects.
How did engineers respond to your study?
May: A lot of people from turbine manufacturers asked if I had considered the technical implications of this. I hadn’t, because I’m an ecologist, not an engineer. Apparently black blades will heat up more than white blades, which may cause structural effects. And the black paint is made with carbon, which could affect the turbine’s performance when hit by lightning. Engineers don’t like that. So we need to overcome these disciplinary silos and work together to develop functional mitigation measures.
This article appears in the June 2025 print issue as “Roel May.”
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