Pre-wind energy development assessment of the avian community in the Central Texas Panhandle

Wind energy development is a fast growing renewable energy source. It has the potential to reduce some of our dependence on fossil-fuels. Despite the many benefits of wind power, there are some concerns regarding the environmental impact of wind turbines, such as habitat loss, habitat disturbance, soil disturbance and possible erosion, vegetation loss, promotion of invasive species, noise pollution, and collision-related avian mortality. The impacts of wind energy development on wildlife can be both direct and indirect. Bird and bat collisions with turbines and other infrastructure are possible direct hazards. Habitat loss, habitat fragmentation, avoidance of structures and other behavioral changes, and increased predation because of increased perching and nesting structures for raptors are some of the potential indirect hazards.

Wind farms likely have varying risks and different magnitudes of hazards depending on placement of the facility, topography, weather, wildlife habitat needs, and wildlife migration patterns. Improvements in wind farm placement and new repellant technologies may help reduce mortality at wind facilities. These wildlife impact issues along with the great potential for wind energy development in the Great Plains has increased the need for pre-construction assessments and mitigation to lessen the potential impacts of wind energy development. My intent was to gain a better understanding of grassland bird communities in the Texas Panhandle. I examined avian flight heights to identify possible species at greater risk of collisions with wind turbines and I examined avian diversity and density patterns through the year. Understanding differences in avian diversity between vegetation types will help wildlife managers and wind energy developers identify areas that may be important to avian conservation. I compared the effectiveness of point-counts and line-transects to help researchers plan avian surveys for future pre-construction assessments.

During October 2008–August 2009, I recorded flight heights of 65 species at a future wind farm in the Texas High Plains. I observed average flight heights of 29 species were within the potential rotor swept zone (RSZ; 32–124 m). Of those species, 6 were listed as species of concern for the Texas High Plains region by Texas Parks and Wildlife Department. I found that the species (n = 14) with >25% of observed flight heights within the RSZ were composed of 21% raptors/vultures, 50% wetland associated species, and 29% passerine/other species. As indicated by flight heights, I found raptor and waterfowl groups were at greatest risk of collision with wind turbines in the central Texas Panhandle. Turbine placement should be avoided in areas with high concentrations of trees which provide nesting habitat for many raptor species. Turbine placement should also be avoided in areas of high raptor prey densities where raptors may concentrate to feed. For wetland associated species I recommend that turbine placement should be avoided near playa wetlands where these species concentrate to feed, roost, and nest.

I stratified our sites into 5 vegetation types (agriculture, breaks, plateau grasslands, playa wetlands, and prairie dog (Cynomys ludovicianus) towns). I calculated Shannon and Simpson’s diversity indices for each site, vegetation type, and season. I found the breaks vegetation type (H’ = 2.96; DS = 0.8907), closest to historic native grassland, had the highest avian diversity and plateau grasslands, primarily non-native, had the lowest avian diversity (H’ = 2.19; DS = 0.7404). I detected the most avian species (n = 95) in agriculture but the lack of nesting habitat in agriculture may reduce its importance to conservation of native grassland birds. I observed moderate avian diversity at playa wetlands and prairie dog towns. Diversity indices, often considered indicative of ecosystem health, are an important component in the assessment of placement of wind facilities. Based on diversity, I recommend wind energy developers avoid construction of wind energy facilities on the breaks, playa wetlands, and prairie dog towns vegetation types. Breaks, playa wetlands, and prairie dog town vegetation types provide habitat to unique segments of the avian community in this region such as declining grassland and shorebird populations.

I estimated density using Program Distance 6.0 for 32 of the 163 species observed. While line-transects took more effort they resulted in a greater number of species detected (23 species with point-counts and 29 species with line-transects). This is likely because more area was covered and birds flushed as observers walked along the line. However, differences between survey techniques depended on season and species. For example, non-breeding season sparrows were detected better with line-transects, likely due to flushing of secretive birds. On the other hand, if surveying breeding season sparrows, either survey technique worked well. I recommend line-transect surveys be used when surveying grassland species and non-breeding season surveys. I recommend point-count surveys when survey effort is limited. Potential impacts on wildlife can be reduced during the development phase of a wind facility by relying on pre-construction site assessments. These assessments need to include proper survey techniques for habitats, species, and seasons of studying, along with species occupancy, species density, animal movement through and within a site, and other behaviors of affected avian species. In the Central Panhandle of Texas I recommend placement of wind turbines be avoided near playa wetlands and raptor nesting areas and focused more in agricultural areas. Also, during non-breeding season surveys or when surveying grassland birds the better survey technique is line-transects. More pre-construction research into avain behaviors that may put at greater risk of collision with wind turbines and more specific habitat uses may be helpful in refining the placement of wind turbine placement.