Investigating the “Lake Effect” Influence on Avian Behavior From California’s Utility-Scale Photovoltaic Solar Facilities

This project examined the so-called lake effect hypothesis that utility-scale solar facilities attract birds by simulating the visual cues birds use to locate water bodies. The study followed three interrelated themes matching the process by which birds could be attracted to solar facilities from: 1) detection by birds of an attractive cue such as polarized light that results in, 2) a corresponding adjustment in flight behavior toward a solar facility that, 3) leads to arrival and interaction of birds at solar facilities, potentially resulting in bird fatalities. Results of field experiments demonstrate that birds can see polarized light in the visible range and use it to make foraging decisions and locate water bodies. Results of solar-panel imaging studies show that both thin-film and polycrystalline panel types polarize reflected sunlight consistent with reflections from water bodies. Animals in flight show strong evidence of descent but not reorientation toward solar facilities, consistent with attraction from a solar cue. Bird fatalities were detected at photovoltaic solar facilities in Southern California more frequently than in surrounding areas. Attraction of aquatic habitat birds to photovoltaic solar facilities is likely a nuanced process; however, such facilities are unlikely to provide the cues of a lake to all aquatic habitat birds at all times. Results from this research are largely consistent with a lake effect hypothesis and could be influential in identifying approaches for reducing impacts on birds (for example, panel technologies that disrupt polarized light transmission). Demon-strating that such solutions can be effective at decreasing avian mortality could lower the regulatory costs of solar energy build-out and production, to the benefit of both California’s ambitious clean-energy mandates and the state’s ratepayers.