Efficacy of Painting Wind Turbine Blades as a Mitigation Measure to Reduce Bird Collisions in a Mediterranean Wind Farm.

One of the most notable impacts of wind energy is bird mortality due to collisions with wind turbines, making it necessary to adopt measures to prevent or mitigate this impact. In recent years, studies have been carried out to test the efficacy of painting wind turbine blades to increase their visibility and forewarn birds, thus preventing collisions. To corroborate these studies in other site- and species-specific settings, we report on a long-term experiment (2012-2024) performed at the El Ruedo wind farm in Cadiz, Spain. One of three rotor blades was painted black at four of the 20 wind turbines, underneath which daily fatality searches were performed both before (9.5 years) and after (3.5 years) treatment. This Before-After-Control-Impact experiment resulted in a significant reduction in bird fatality rates of 74% at the painted turbines relative to unpainted control turbines. The treatment had the largest effect in reducing passerine fatalities as well as large waterbirds, but less so for birds of prey. To which extent local abundance, flight activity or visual fields affect the measure's efficacy remains as yet unclear. As this mitigation measure has now been shown to be functional at sites spanning a wide latitudinal range, it is paramount to overcome implementation hurdles and evaluate other site- and species-specific conditions.