By Edward J. Raynor, Larkin A. Powell, and Jennifer A. Smith
Linked paper: Anthropogenic noise does not surpass land cover in explaining habitat selection of Greater Prairie-Chicken (Tympanuchus cupido) by E.J. Raynor, J. Olney Harrison, C.E. Whalen, J.A. Smith, W.H. Schacht, A.J. Tyre, J.F. Benson, M. Bomberger Brown, and L.A. Powell, The Condor: Ornithological Applications.
Imagine living in a grassland landscape with an almost constant low-frequency hum from spinning wind turbine blades. The humming is distracting, so what do you do? You could move to a quieter area where the turbine noise would be less disturbing. But our research shows that if you’re a Greater Prairie-Chicken, one of North America’s most threatened grassland birds, you’re more likely to stay put.
Our research team previously reported that sites within one kilometer of wind turbines had higher-than-expected background noise due to the turbines’ proximity. However, we also found that sound levels (i.e. the amount of noise) from wind turbines can be affected by wind direction, wind speed, topography, and many other factors. Such factors are important for determining how far male Greater Prairie-Chicken vocalizations carry.
We had already found that prairie-chickens did not select nest sites based on the straight-line distance to the nearest wind turbine. However, that study didn’t address all the nuanced mechanisms that could influence prairie-chickens’ space use and site selection. Here, we used a mechanistic approach to model the spread of noise from wind turbines and used the output to evaluate the effect of noise on site selection by prairie-chickens. Even with this approach, noise levels did not affect prairie-chicken habitat selection during the breeding season.
Why did Greater Prairie-Chickens appear to ignore wind turbine noise? In other studies, Greater Sage-Grouse have responded to noise from natural gas drilling and roads with elevated stress levels and declines in male attendance at leks exposed to noise playback. However, it’s possible that wind turbines simply aren’t loud enough to be meaningful to a prairie-chicken in the course of its daily decisions. In addition, Greater Prairie-Chickens are ground-dwelling birds that forage on seeds and insects on or near the ground. The sound levels from wind turbines are lessened closer to the ground, so prairie-chickens are likely not exposed to the full noise levels emitted by the turbines.
A study in Kansas using a before/after experiment found that Greater Prairie-Chickens avoided areas near wind turbines and doubled the size of their home range after wind energy facility construction. However, our research was conducted at least eight years after the construction of the wind energy facility. The average lifespan of a Greater Prairie-Chicken is roughly two years, so at least four generations of Greater Prairie-Chickens have existed on this landscape since the construction of the wind energy facility at our site. Therefore, this population of Greater Prairie-Chickens may have adjusted to the presence of wind turbine noise over time. In addition, our research occurred in a rangeland system with a road density at a level one-third that of the study site in Kansas. It’s possibly that when grasslands are already fragmented, the addition of a wind turbine facility may be enough to cause birds to avoid the area.
So if prairie-chickens at our site aren’t choosing where to spend their time based on wind turbine noise, what factors do they care about? Our findings show that the presence of trees and row crops in the prairie-chickens’ breeding habitat in the Nebraska Sandhills overrides the effects of wind turbines. Previous work on this species in southern Nebraska and elsewhere in the Great Plains has documented avoidance of wooded areas, and our work adds to the evidence that this species avoids patches of trees in a contiguous grassland. This finding is a cause for conservation concern, because woody encroachment is a growing threat throughout the present-day range of the Greater Prairie-Chicken.
Our study is the first to show that noise levels can be mapped and used in a similar manner to spatial assessments of the effects of predator density or other measures of predation risk commonly used in resource selection studies. We hope that our research provides the impetus for further understanding of acoustic habitat selection and serves as a stepping stone for managing grassland environments exposed to acoustic disturbances and woody encroachment.