Effects of wind turbine noise on the surrounding soundscape in the context of greater-prairie chicken courtship vocalizations

Abstract

The development of wind energy facilities in grasslands has increased in recent years. We assessed sound levels near a 36-turbine wind energy facility in a contiguous grassland in Brown County, Nebraska, USA, using a grid sampling design. Greater prairie-chickens (Tympanuchus cupido pinnatus), a bird species of special conservation concern, occupy the landscape near the wind facility. We evaluated the variation in wind turbine noise in the landscape at 296 Hz, the average peak frequency of the critically important courtship (‘boom’) vocalization of male prairie-chickens. The levels of ambient sounds were affected by ordinal day (β = −0.0752, SE = 0.0073) and wind speed (β = 1.1679, SE = 0.0419). Sound levels (dB) at the wind facility were affected by distance to the nearest turbine (β = 0.6917, SE = 0.0111). Sound levels increased during the breeding season (ordinal day: β = 0.0166, SE = 0.0028), during the day (time of day: β = 0.0035, SE = 0.0015), and at higher wind speeds (β = 1.1929, SE = 0.0261). Sound levels were higher downwind from the facility (wind direction: β = 0.9914, SE = 0.1691) and at sites that were within the viewshed of turbines (topography: β = 0.3819, SE = 0.0824). At 100 m from the turbines, under average temporal, landscape, and wind conditions, wind turbine noise at 296 Hz was 25 dB above the ambient sound level. At 500 m from the turbines, wind turbine noise at 296 Hz was 16 dB above the ambient sound level. Our results demonstrate the variation of wind turbine noise in the soundscape and suggest a protocol for evaluating effects of wind turbine sound on sound-sensitive wildlife.