Fatal attraction: migratory bats are lured to wind turbine blades

Wind turbines are important for global energy production because of their low greenhouse gas emissions. However, for unknown reasons, many migratory bats are colliding with the wind turbine blades, leading to mass die-offs. As vision plays an important role for bats as they fly, often allowing them to avoid obstacles, one thought is that bats are visually attracted to wind turbines, causing them to mistakenly fly towards and fatally collide with the fast-moving blades. This idea led independent researcher Kristin Jonasson (USA) and researchers from the University of Colorado Colorado Springs, the National Renewable Energy Laboratory and the USDA Forest Service Pacific Southwest Research Station (all in the USA) to determine whether two of the most common migratory bat species affected by wind turbines in North America – hoary bats (Lasiurus cinereus) and silver-haired bats (Lasionycteris noctivagans) – were visually attracted to light reflecting off wind turbine blades.Between 15 September and 13 October 2024, the team caught 242 hoary and 154 silver-haired bats in Humboldt Redwoods State Park (CA, USA). They then transported the bats in cloth bags a short distance to a location where they had built a large Y-shaped structure, known as a Y-maze, for the bats to fly through. At the end of one of the two arms, the researchers placed an industry standard, glossy, white-painted decommissioned wind turbine blade illuminated by a light replicating moonlight. At the end of the other arm, the researchers placed a matte black-painted decommissioned wind turbine blade illuminated with replicated moonlight or an unlit matte black-painted decommissioned wind turbine blade, or they removed the wind turbine blade entirely and left the arm dark and empty. The researchers then released the bats individually into the maze, filming the animals as they flew through the structure and selected one arm of the maze or the other, while also recording their echolocation clicks, to find out whether the bats are attracted to the simulated moonlight reflecting off the white or the black wind turbine blades.The researchers found that both species flew through the arm of the Y-maze with the illuminated white-painted wind turbine blade twice as often as the arm with the matte black-painted wind turbine blade (lit or unlit) or with no wind turbine blade. From this, they concluded that bats are likely attracted to the simulated moonlight reflected from the wind turbine blade. Additionally, the bats chose the white-painted wind turbine arm more often than the dark empty maze arm (97% of hoary bats and 74% of silver-haired bats), suggesting that these bats prioritize vision over echolocation as they navigate through the air, even though all of the bats were confirmed to be echolocating while they were flying.Overall, Jonasson and colleagues have successfully shown that two North American migratory species of bats are visually attracted to moonlight that reflects off wind turbine blades. A future step in protecting these bats is to make sustainable changes to wind turbines, so they can continue generating electricity while ensuring that bats are not in peril from their fast-moving blades.