Gregory D. Johnson

Ecological impacts of wind energy development on bats: questions, research needs, and hypotheses

At a time of growing concern over the rising costs and long-term environmental impacts of the use of fossil fuels and nuclear energy, wind energy has become an increasingly important sector of the electrical power industry, largely because it has been promoted as being emission-free and is supported by government subsidies and tax credits. However, large numbers of bats are killed at utility-scale wind energy facilities, especially along forested ridgetops in the eastern United States. These fatalities raise important concerns about cumulative impacts of proposed wind energy development on bat populations. This paper summarizes evidence of bat fatalities at wind energy facilities in the US, makes projections of cumulative fatalities of bats in the Mid-Atlantic Highlands, identifies research needs, and proposes hypotheses to better inform researchers, developers, decision makers, and other stakeholders, and to help minimize adverse effects of wind energy development.

Patterns of Bat Fatalities at Wind Energy Facilities in North America

Abstract Wind has become one of the fastest growing sources of renewable energy worldwide, but widespread and often extensive fatalities of bats have increased concern regarding the impacts of wind energy development on bats and other wildlife. We synthesized available information on patterns of bat fatalities from a review of 21 postconstruction fatality studies conducted at 19 facilities in 5 United States regions and one Canadian province. Dominance of migratory, foliage- and tree-roosting lasiurine species (e.g., hoary bat [Lasiurus cinereus]) killed by turbines was consistent among studies. Bat fatalities, although highly variable and periodic, consistently peaked in late summer and fall, coinciding with migration of lasiurines and other species. A notable exception was documented fatalities of pregnant female Brazilian free-tailed bats (Tadarida brasiliensis) in May and June at a facility in Oklahoma, USA, and female silver-haired bats (Lasionycteris noctivagans) during spring in Tennessee, USA, and Alberta, Canada. Most studies reported that fatalities were distributed randomly across turbines at a site, although the highest number of fatalities was often found near the end of turbine strings. Two studies conducted simultaneously in the same region documented similar timing of fatalities between sites, which suggests broader patterns of collisions dictated by weather, prey abundance, or other factors. None of the studies found differences in bat fatalities between turbines equipped with lighting required by the Federal Aviation Administration and turbines that were unlit. All studies that addressed relationships between bat fatalities and weather patterns found that most bats were killed on nights with low wind speed (<6 m/sec) and that fatalities increased immediately before and after passage of storm fronts. Weather patterns may be predictors of bat activity and fatality; thus, mitigation efforts that focus on these high-risk periods could reduce bat fatality substantially. We caution that estimates of bat fatality are conditioned by length of study and search interval and that they are biased in relation to how searcher efficiency, scavenger removal, and habitat differences were or were not accounted for. Our review will assist managers, biologists, and decision-makers with understanding unifying and unique patterns of bat fatality, biases, and limitations of existing efforts, and it will aid in designing future research needed to develop mitigation strategies for minimizing or eliminating bat fatality at wind facilities.

Avian Collisions with Wind Turbines: A Summary of Existing Studies and Comparisons to Other Sources of Avian Collision Mortality in the United States

It has been estimated that from 100 million to well over 1 billion birds are killed annually in the United States due to collisions with human-made structures, including vehicles, buildings and windows, powerlines, communication towers, and wind turbines. Although wind energy is generally considered environmentally friendly (because it generates electricity without emitting air pollutants or greenhouse gases), the potential for avian fatalities has delayed and even significantly contributed to blocking the development of some windplants in the U.S. Given the importance of developing a viable renewable source of energy, the objective of this paper is to put the issue of avian mortality associated with windpower into perspective with other sources of avian collision mortality across the U.S. The purpose of this paper is to provide a detailed summary of the mortality data collected at windplants and put avian collision mortality associated with windpower development into perspective with other significant sources of avian collision mortality across the United States. We provide a summary of data collected at many of the U.S. windplants and provide annual bird fatality estimates and projections for all wind turbines in the U.S. For comparison, we also review studies of avian collision mortality from other major human-made structures and report annual bird fatality estimates for these sources. Other sources also significantly contribute to overall avian mortality. For example, the National Audubon Society estimates avian mortality due to house cats at 100 million birds per year. Pesticide use, oil spills, disease, etc., are other significant sources of unintended avian mortality. Due to funding constraints, the scope of this paper is limited to examining only avian mortality resulting from collisions with human-made obstacles.

Mortality of Bats at a Large-scale Wind Power Development at Buffalo Ridge, Minnesota

Abstract In 1994 a major wind power development project was initiated in southwest Minnesota that may eventually produce 425 megawatts (MW) of electricity. The wind plant currently consists of 3 phases that total 354 turbines capable of generating 236 MW. During a study conducted from 1996–1999 to assess effects of wind power development on wildlife, 184 bat collision fatalities were documented within the wind plant. Hoary bats (Lasiurus cinereus) and eastern red bats (L. borealis) comprised most of the fatalities. After correcting bat fatality estimates for searcher efficiency and scavenger removal rates, we estimated that the number of bat fatalities per turbine ranged from 0.07 per y at the Phase 1 wind plant to 2.04 per y at the Phase 3 wind plant. The timing of mortalities, and other factors, suggest that most mortality involves migrant rather than resident breeding bats.

Bat activity, composition, and collision mortality at a large wind plant in Minnesota

Abstract We examined bat activity levels, species composition, and collision mortality at a large wind plant in southwest Minnesota from 15 June-15 September, 2001 and 2002. We found 151 bat casualties, most of which were hoary bats (Lasiurus cinereus). We recorded 3,718 bat passes at bat foraging and roosting areas within 3.6 km of the wind plant (x̄ = 48/detector-night) and 452 bat passes at wind turbines (x̄ = 1.9/detector-night). Peak bat activity at turbines followed the same trend as bat mortality and occurred from mid-July through the end of August. Based on the timing of fall bat migration, we believe that most bat mortality involved migrating bats. There was no significant relationship between bat activity at turbines or the number of fatalities and presence of lights on turbines. We captured 103 bats comprised of 5 species in mist nets. Big brown bats (Eptesicus fuscus) comprised most of the captures. Our study indicated that there were relatively large breeding populations of bats near the wind plant when collision mortality was low to nonexistent. Future research should concentrate on determining causes of bat collisions and methods to reduce or mitigate the mortality.

QUANTIFYING IMPACTS TO RIPARIAN WETLANDS ASSOCIATED WITH REDUCED FLOWS ALONG THE GREYBULL RIVER, WYOMING

Reductions in river flows associated with hydrologic changes from diversions may reduce water elevations and impact hydrology of riparian wetlands. The U.S. Army Corps of Engineers and other federal agencies currently do not have appropriate tools to evaluate effects of hydrologic changes on wetlands. We describe use of HEC-RAS modeling to predict and quantify wetland impacts along 10 km of the Greybull River, Wyoming, USA following a proposed 28,313 L/sec diversion for a new off-channel reservoir. Riparian wetlands were delineated and mapped on aerial photographs and topographic maps. A water-surface-profile model of the river was developed using the HEC-RAS model. Floodplain boundaries with and without the diversion were plotted to the same scale and overlaid on the wetland maps to estimate area of wetlands that would not be flooded under the reduced flow model. The model predicted that total area flooded under the 28,313 L/sec diversion in the reach analyzed would be reduced from 167.2 to 149.7 ha and that approximately 0.47 ha of wetland would be impacted by the diversion. We believe that the procedure we used is a valid method to quantify effects of diversion on riparian wetlands and that this procedure should be further evaluated as a method to assess wetland impacts on similar projects.

Assessing river habitat selection by waterfowl wintering in the South Platte River, Colorado

We assessed river habitat selection of waterfowl wintering in the South Platte River below the Metro Wastewater Reclamation District treatment plant in Adams County, Colorado to determine potential impacts of proposed river channel modifications. Daily mean number of waterfowl was 711 per km of river over the study area, and 19 species of waterfowl were observed. We describe use of a resource selection model to evaluate whether a habitat type is selected more than expected based on its availability. Habitat selection indices indicated that Canada geese (Branta canadensis) used all habitats in proportion to their availability. Dabbling ducks selected large pools, secondary channels, riffles and sandbars, avoided smaller pools and islands, and used runs in proportion to their availability. Diving ducks selected large pools, small pools, and runs; they avoided secondary channels, riffles, sandbars, and islands. Due to different habitat preferences between diving and dabbling ducks, changes that alter river habitat structure may favor some species and not benefit others. The optimum way to maintain diversity and abundance of waterfowl wintering in the South Platte River is to maintain a variety of habitat types.