Post-construction monitoring studies at several dozen wind-energy facilities across the U.S. have provided a general picture of direct impacts to bird and bats: passerines are the bird group most commonly found as collision-related fatalities; tree-dwelling bats (genus Lasiurus and Lasionycteris) are the most common bat fatalities. However, as post-construction data from additional wind-energy facilities become available, some initial hypotheses about the potential for wind-energy impacts to birds and bats have been contradicted. For example, projects in West Virginia, Pennsylvania, and Tennessee had bat fatalities that were exceptionally high compared to projects in other parts of North America (Arnett et al. 2008). It was believed that the location of the projects on forested ridgetops was a main reason that bat fatalities were highest at these wind projects (e.g., Kunz et al. 2007), but recent results from Alberta, Canada, and Wisconsin indicate that bat fatality rates can also be high at projects located in flatter areas used for cultivated agriculture and lacking the continuous tree cover notable on eastern forested ridges.
Publicly-available post-construction wind-energy impacts data are summarized from 19 studies at 16 wind-energy projects in the U.S. that use wind turbines of modern design. Publicly available data come from sources such as journal articles, documents released as part of permitting processes, or information posted on non-password-protected websites. Other wind projects may have had data collected, but if those data are not available in a public forum, they will not be discussed here. Most publicly-available studies are from grasslands and agricultural lands in the arid west. Post-construction monitoring results from other parts of the U.S. such as the wooded ridges along the eastern seaboard may be less relevant to Minnesota since they generally are located where topography, climate, vegetation, and wildlife use are different, but some projects from the eastern states will be reviewed in this document because they are the only wind-energy impact studies in landscapes dominated by forests, or where lakes or wetlands are abundant.
The Minnesota Department of Natural Resources (MDNR) and the U.S. Forest Service have developed an Ecological Classification System (ECS) for ecological mapping and landscape classification in Minnesota (http://www.dnr.state.mn.us/ecs/index.html). Ecological land classifications are used to identify, describe, and map progressively smaller areas of land with increasingly uniform ecological features. The system uses associations of biotic and environmental factors, including climate, geology, topography, soils, hydrology, and vegetation. ECS mapping enables resource managers to consider ecological patterns for areas of varying scale and identify areas with similar management opportunities or constraints relative to that scale. Map units for six of these levels occur in Minnesota (Provinces, Sections, Subsections, Land Type Associations, Land Types, and Land Type Phases). Four Provinces occur in Minnesota (Prairie parkland, Tallgrass aspen parklands, Eastern broadleaf forest, and Laurentian mixed forest; Figure 2) and are considered in this report.
The Province for which there are the most post-construction impact studies in comparable habitat is Prairie Parkland, with a relatively arid climate and landcover dominated by grassland and cultivated agriculture. Most wind-energy development in Minnesota has taken place in the Prairie Parkland Province, though this is changing as more projects are considered in other Provinces. Many wind-energy impact studies may also be applicable, in terms of landcover, to the Tallgrass aspen parklands Province since the climate is arid, and cold, dry winters coupled with spring wildfires prevent woody vegetation from becoming dense. However, the Tallgrass aspen parklands have more open woodlands and wetlands than most of the landscapes where wind-energy projects are currently operating.
The Eastern broadleaf forest Province extends from the southeast corner of Minnesota up to the center of the state and is a transition zone between the prairies to the west and the wetter mixed forests of the northeast. Presettlement vegetation was a mixture of forests, woodlands, and patches of fire-maintained prairie, but much of the Province has been converted to cultivated agriculture or human development. The Laurentian mixed forest Province covers a large portion of Minnesota in the north and east. It is characterized by coniferous forests, mixed forests, lakes, and coniferous bogs and swamps. There are few studies of wind-energy development impacts in landtypes similar to the Eastern broadleaf and Laurentian mixed forest Provinces; some published studies in forested areas are available from New York and Pennsylvania.
Studies of direct and indirect bird and bat impacts due to wind energy facilities are described in this document, and then related to Minnesota by ecological Province. The commercial-scale facilities summarized in this report (Table 1, Table 2) use turbines with capacities ranging from 0.3 to 2.0 MW, have turbines mounted on tubular towers that do not provide perching spots for birds, and have electrical collection lines buried to reduce electrocution risk for birds. The 0.3-MW turbines that were constructed in 1994 at Buffalo Ridge, MN, are much smaller in terms of height and capacity than turbines typically built in 2010, which have taller towers and capacity of 1.5-2.5 MW. Results from the Buffalo Ridge studies are outdated and may not be relevant due to changes in turbine size; however, the Buffalo Ridge studies remain the most rigorous evaluations of wind-energy impacts in the region.