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

Article excerpt

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.


Wind has been used to commercially produce energy in North America since the early 1970s [American Wind Energy Association (AWEA), 1995]. Recent advances in wind turbine technologies have reduced costs associated with wind power production (Hansen et al., 1992), and wind power produced in the United States in 2001 was comparable in price to conventional power produced using natural gas [American Wind Energy Association (AWEA), 2001]. Commercial wind plants have been constructed in 26 states (Anderson et al., 1999; AWEA, 2002). Although generally considered environmentally friendly, wind power has been associated with the deaths of birds colliding with turbines and other wind plant structures, especially in California. As a result of these concerns, state and federal agencies require monitoring of many new wind development areas to assess the extent of and potential for avian mortality from collision with turbines.

In 1999 development of a 354-turbine wind plant was completed on Buffalo Ridge in southwestern Minnesota (Fig. 1). Avian monitoring studies were initiated during completion of the first 73 turbine phase of the facility in 1994. An unexpected outcome of these monitoring studies was the discovery of 13 bat fatalities near turbines during the first 2 y of operation (Osborn et al., 1996). We conducted additional monitoring studies at the expanded wind plant from 1996-1999. Although our study was designed primarily to assess effects of wind power development on birds, data collected during fatality searches also allowed us to address wind power impacts on bats. Our objectives were to estimate the number of bal mortalities attributable to collisions with wind turbines for the entire Buffalo Ridge wind plant, to determine the species and groups at highest risk and to determine what factors might be related to the collision mortality.


The study area was comprised of a large portion of Buffalo Ridge, a 100-km-long segment of the Bemis Moraine located in southwest Minnesota and northeast South Dakota (Fig. 1). Buffalo Ridge is located in the Coteau des Prairies, a major physiographic landform consisting of terminal moraines and stream-dissected lands (Coffin and Pfannmuller, 1988). The ridge runs diagonally from southeast to northwest and separates the Missouri and Mississippi river watersheds. Elevations range from 546 m to 610 m above sea level. Vegetation types consist primarily of corn, soybeans, small grains and hay; pasture; and Conservation Reserve Program (CRP) grasslands. Less prevalent vegetation types include deciduous woodlots associated with farmsteads, wooded ravines and wetlands. Vegetation, including vertical density and vegetation height, has previously been described for cropland, pasture and CRP habitats in the Buffalo Ridge study area (Leddy, 1996).

The wind plant currently consists of three major phases of development (Fig. 1). Phase 1, constructed in 1994, consists of 73 turbines and related facilities, including distribution lines, meteorological towers, communication systems, transformers, substations, roads and operations and maintenance facilities. …