The main concern regarding the impact of wind turbines on birds and bats is mortality caused by collisions with rotating turbine blades.  To a lesser extent there is also some concern about habitat fragmentation caused by the placement of turbines.  This is a less controversial issue however, because it can be controlled by careful placement of turbines.  Avian and bat impacts with blades are more difficult to predict and control however, therefore most research has focused on mortality caused by collisions.

There have been several studies conducted in North America and in Western Europe that have researched the impacts of turbines on avian populations. Unfortunately, because such studies require large time commitments the results are limited. In addition, because the results are highly dependent upon the environmental conditions at each location, they are difficult to apply over large regions. Therefore, the variances in the results of the studies make it difficult to draw conclusions about the impact of turbines.

One of the most notable avian impact studies was conducted in the Altamont Pass region of California between March 1998 and December 2000. During the period of study the region contained over 5,400 operating wind turbines. Over 400 avian deaths were reported in the study, with over 50% classified as raptors such as eagles and hawks. The large number of deaths sparked some concerns within the wind energy community, which was further heightened by the fact that many of the raptors were protected under California law.

Since the Altamont study, improvements in turbine technology as well as additional research have helped to dispel some of the initial concerns about avian impact. One of the improvements has included an a switch from lattice to tubular tower design. The original lattice structures caused increases in bird deaths because birds used the rungs of the structures for resting and nesting.  Because high concentrations of birds were drawn to the structures, more birds were struck by the rotating blades. Changes to the tubular tower design have decreased the amount of birds drawn to the structures and thus have reduced mortality. 

In addition to changes in tower design, slower rotor speeds and changes in tower lights have helped to reduce avian and bat mortality in some turbine studies. In November 2004 the National Wind Coordinating Committee (NWCC) analyzed a number of these national turbine studies in an effort to consolidate the results for various regions of the United States . The findings conclude that turbines are responsible for some avian and bat deaths, although the specific impact is highly dependant on the environment in question and the size and type of turbine. The results show that the average bird mortality rate is 2.3 birds/turbine/year and the average bat mortality rate is 3.4 bats/turbine/year. For comparison, house cats alone are responsible for the death of 1 billion birds each year in the U.S.   This is approximately 10% of the human-related bird deaths each year. 

In addition to the number of birds killed per turbine, the study found that both migrating and resident birds and bats are affected by turbines. It also appears that songbirds are less affected than other bird varieties and that the number of raptors affected is unusually high in the Altamont study. The amount of research on bat populations to date has been limited so the study draws few specific conclusions about bat impact.

Because the amount of research conducted is still very limited (though ongoing), the U.S. Fish and Wildlife Service issued some interim guidelines in 2003 that can minimize turbine impacts on wildlife, specifically birds and bats. Some of the recommendations include:

•  Avoid placing turbines near migratory pathways or known habitats with high concentrations

•  Avoid siting turbines near cliffs and ridges that can attract raptors

•  Avoid areas that may contain species of protected birds and bats

•  Minimize infrastructure and avoid fragmenting tracts of wildlife habitat

•  Use tubular rather than lattice towers, and minimize use of guy wires

•  Towers taller than 199 ft. should use only white lights at night and should use the lowest intensity and lowest intermittency lights possible

•  Turbines should be monitored for 3 years for impacts on birds and bats

•  Turbines should be turned off to accommodate peak migratory concentrations of birds when possible

The Upper Peninsula is home to various bat species that reside in many of the historic mines in the area. In addition, the U.P.’s forested environment makes it an ideal habitat for a variety of bird species, including several threatened species such as the Bald Eagle and Kirtland’s Warbler. Specifically, Michigan hosts approximately 175 songbird species throughout the year. In addition, the Upper Peninsula hosts approximately 20 species of raptors. Of the songbirds and raptors in Michigan , 95% are migratory which means that they either reside in the state for only a portion of each year or use the state as a flyway during the migratory season. These migratory species are especially important because they are the most susceptible to collisions with turbines.

Various areas in the U.P. are used by birds during their migratory flights, but one especially important area is located near Brockway Mtn. in the Keweenaw Peninsula . This region is globally important because over 40,000 migratory raptors fly through the area each spring. The majority of the migration occurs during late April and early May. The birds tend to fly on the inland ridges of the peninsula because they prefer to avoid open waters. In addition, the majority of these raptors are daytime migrants. Because the area hosts a large concentration of birds, special care should be taken when placing turbines in the area. One possibility that could help to reduce the impact on the birds may include turning off any turbines in late spring when the peak migration occurs. To help ensure a minimum impact on the birds, research should be conducted before siting turbines in the Western U.P.

The NWCC study mentioned above involved four studies conducted throughout the upper Midwest including parts of Minnesota and Wisconsin , although no specific research was performed in Michigan . The study found that the average bird mortality rate for the upper Midwest is 2.7 birds/turbine/year, which is slightly higher than the national average. The study found no impact on raptors in the region. The mortality rate of bats for the area was found to be 1.7 bats/turbine/year, which is only half of the national average. It is important to note that this data is generalized for the Midwest , including Michigan . Therefore before siting any turbines in Michigan and the Upper Peninsula , research should be conducted in the specific area.

For more information about the bird and bat species in Michigan go to the Michigan Department of Natural Resources (DNR) website.

Information about the status of various bird and bat species in Michigan can be found through the Michigan Natural Features Inventory , which lists the current status of species by county. In addition the Michigan DNR website provides an interactive mapping tool that allows the user to conduct an endangered species assessment to find unique natural features and listed species within each region of the state.

Wind Power in the Western Upper Peninsula