Assessment of Diurnal Wind Turbine Collision Risk for Grassland Birds on the Southern Great Plains

Abstract

AbstractWind energy is one of the fastest growing renewable energy sources in the United States and has the potential to reduce the use of traditional nonrenewable energy. However, there is concern for potential short- and long-term influences on wildlife populations, such as bird collisions with turbine blades, habitat loss, habitat fragmentation, and habitat avoidance. Bird flight heights are indicative of collision risks, but knowledge of their distributions is limited. Our goal was to examine the diurnal flight heights of bird species to assess which are at greatest risk of collision with wind turbine blades. During October 2008–August 2009, we estimated the flight heights of 66 bird species at a planned wind energy facility on the southern Great Plains. Flight heights were estimated by measuring angle of incline with a clinometer and ground distance with a laser rangefinder. Previous work has been limited to flight height measurements categorized to site-specific rotor swept zone (RSZ) specifications that has resulted in limited applicability to other wind turbine RSZ specifications. Our research is distinctive because it provides more resolution in flight height estimates than those categorized into bins and allows application to wind turbines with different RSZs. We found that the flight heights of six bird species varied among seasons, indicating their risk of collision changed throughout the year. Observations indicated that the average flight heights of 28 bird species were within the potential RSZ (32–124 m above ground level) at our study site and that two species exhibited mean flight heights above the RSZ. Fifteen of those species were wetland-associated species, 7 were raptor or vulture species, and 6 were listed as species of greatest conservation need by Texas Parks and Wildlife Department. We observed 14 bird species (1 vulture, 2 raptors, 7 wetland-associated species, and 4 passerines or other species) with greater than 25% of their observed flight heights within the RSZ. Our results indicate that raptors and wetland-associated species are the avian groups at greatest risk of collision with wind turbines due to their diurnal flight heights. However, the resolution of our data will allow assessment of which bird species are at greatest risk of collision for various wind turbine specifications. This information can help guide site assessment and placement for wind energy facilities across the southern Great Plains and help mitigate potential collision impacts on bird species.