Bird Flight Characteristics near Wind Turbines in Minnesota
Osborn, Robert G., Dieter, Charles D., Higgens, Kenneth F., Usgaard, Robert E., The American Midland Naturalist
ABSTRACT.-During 1994-1995, we saw 70 species of birds on the Buffalo Ridge Wind Resource Area. In both years bird abundance peaked in spring. Red-winged blackbirds (Agelaius phoeniceus), mallards (Anas platyrhynchos), common grackles ( Qiscalus quiscula), and barn swallows (Hirundo rustica) were the species most commonly seen. Most birds (82-84%) flew above or below the height range of wind turbine blades (22-55 m). The Buffalo Ridge Wind Resource Area poses little threat to resident or migrating birds at its current operating level.
Recent improvements in wind turbine technologies have reduced the costs associated with wind power production, and have increased interest in the use of wind energy as an alternative energy source. However, a problem associated with wind power development has been bird mortality from collisions with wind turbines (McCrary et al., 1986; Howell and Noone, 1992; Orloff and Flannery, 1992).
Although the reasons that birds collide with wind turbines are not well understood, several factors have been identified (Nelson and Curry, 1995). Many of these factors, such as storm fronts (which increase a bird's rate of travel) and fog (which reduces visibility) are uncontrollable. Others factors, such as topography, surrounding land use, and the presence of dense breeding or wintering avian populations are partially controllable or avoidable through habitat manipulation or presite reconnaissance. However, even a well-sited facility may be the occasion of some bird mortality. As a result, most research has focused on finding ways to decrease the likelihood of bird/turbine collisions.
Bird collisions with wind turbines are rare and few have been witnessed (Nelson and Curry, 1995). Birds can detect the presence of wind turbines and generally avoid them. However, some birds become habituated to wind turbines and readily fly through strings of nonoperational turbines or use wind turbines as perching sites (Nelson and Curry, 1995). Therefore, wind power companies, utility companies, and state and federal natural resource agencies have modified structural characteristics of wind turbines to reduce their attractiveness to birds, to increase their visibility to birds and to make them more difficult for perching or nesting. For example, replacing lattice frame towers with tubular towers has been used successfully to reduce perching and nesting sites. Currently, tests are being conducted to determine if painting turbine blades with different colors or patterns might reduce the frequency of collisions with turbines.
In the autumn of 1993, a site in southwestern Minnesota, known as Buffalo Ridge, was selected as the location of Minnesota's first windplant. A preconstruction reconnaissance of the Buffalo Ridge site concluded that the impact of the windplant on birds would likely be minimal, but that the vulnerability of each species would be directly related to abundance and flight patterns (Nelson, 1993).
In April 1994, near the completion of the first phase (25 megawatts) of a proposed 425megawatt facility, KENETECH Windpower contracted with South Dakota State University and the South Dakota Cooperative Fish and Wildlife Research Unit to conduct avian research on the Buffalo Ridge Wind Resource Area (WRA) near Lake Benton, Minnesota. One purpose of this research was to monitor the seasonal movements, relative abundance and activity patterns of birds in relation to wind turbines; another was to document the behavior and activity of individuals or groups of birds to determine which species may be most susceptible to collisions with wind turbines.
Study area.-Buffalo Ridge is located in southwestern Minnesota and is a 100-km segment of the Bemis Moraine that runs NW to SE, separating the Missouri River and Mississippi River watersheds. It is located in the Coteau des Prairies physiographic region and consists of terminal moraines and stream-dissected upland prairie and prairie wetlands (Coffin and Pfannmuller,1988). …