Bats and Wind Energy—A literature synthesis and annotated bibliography
This document, prepared in cooperation with the U.S. Fish and Wildlife Service, provides a current review of bat mortality due to wind turbines. The executive summary is shown below. The full report can be accessed by selecting the link at the bottom of the page.
Turbines have been used to harness energy from wind for hundreds of years (Gipe, 2004). However, with growing concerns about climate change, wind energy has only recently entered the mainstream of global electricity production. In 2010, the global installed capacity for wind energy reached 196,630 Megawatt (MW), which represents approximately 2.5 percent of the total global energy consumption (World Wind Energy Report, 2010). In the United States, the total utility-scale wind power capacity through the 3rd quarter of 2011 totaled 43,461 MW and this represents more than 20 percent of the world's installed wind power (American Wind Energy Association, 2012). In 2011, the electricity produced from wind energy in the United States amounted to 120 Terawatt-hours (thousand MW) or 2.9 percent of total global electricity demands (U.S. Energy Information Administration, 2012). Canada is the ninth largest producer of wind energy in the world with current installed capacity at 4,862 MW, representing about 2.1 percent of Canada's total electricity demand (Canadian Wind Energy Association, 2012).
Since early on in the development of wind-energy production, concerns have arisen about the potential impacts of turbines to wildlife; these concerns have especially focused on the mortality of birds. Early styles of turbines appeared to pose a greater risk to birds in terms of collision mortality than more modern turbines do (Erickson and others, 2002; Young and others, 2003). Early turbines were smaller, had a higher blade-rotation rate, and had a lower energy output. This resulted in more turbines being needed for significant electricity production, thereby increasing the chances of birds encountering turbines (Curry and Kerlinger, 2000; Erickson and others, 2002; Howell, 1995). The lattice towers of smaller turbines also provided birds with perching opportunities, which was thought to further increase mortality (Kerlinger, 2002; Orloff and Flannery, 1992; Osborn and others, 1998). Structural changes and improved turbine design have been instrumental in reducing mortality in birds (Johnson and others, 2002; Smallwood and Karas, 2009). For example, during a study at the Altamont Pass Wind Resource Area in California, it was found that when comparing the concurrently operating old-generation, smaller turbines during 2005-2007, adjusted fatality rates in the newer, larger, and taller turbines were 66 percent lower for all birds combined.
Despite the improvements to turbines that have resulted in reduced mortality of birds, there is clear evidence that bat mortality at wind turbines is of far greater conservation concern. Larger and taller turbines actually seem to be causing increased fatalities of bats (Barclay and others, 2007). Bats of certain species are dying by the thousands at turbines across North America, and the species consistently affected tend to be those that rely on trees as roosts and most migrate long distances (Cryan and Barclay, 2009). Bat mortality at wind-energy facilities was first documented in Australia, where 22 white-striped mastiff-bats (Tadarida australis) were found at the base of turbines over 4-year (yr) period (Hall and Richards, 1972). In 1999, 45 dead bats were found at a wind energy facility in Carbon County, Wyoming; 10 dead bats were found at a wind energy facility in Umatilla County, Oregon; and 34 dead bats were found within a wind energy facility in Wisconsin (Keeley and others, 2001). Small numbers of dead bats have also been found at wind-energy facilities in California (Orloff and Flannery, 1992; Howell, 1997; Anderson and others, 2000; Thelander and Rugge, 2000). Turbine-related bat mortalities are now affecting nearly a quarter of all bat species occurring in the United States and Canada. Most documented bat mortality at wind-energy facilities has occurred in late summer and early fall and has involved tree bats, with hoary bats (Lasiurus cinereus) being the most prevalent among fatalities.
Populations of bats are difficult to monitor (O'Shea and others, 2003). Because of this, there is insufficient information on the population status of the 45 species of bats in the United States, especially for migratory foliage- and tree-roosting bats (O'Shea and others, 2003). With this lack of understanding of total population sizes, demographics, and impacts of fatalities from wind turbines on the viability of affected bat populations, it is currently not possible to determine the influence of any single source of mortality or of any effects of mitigation strategies on these bat populations. In addition to the direct effects of wind-energy development on bat mortality, indirect effects may occur as well. Bats have low reproductive rates and generally give birth to a single individual once a year. This results in bat populations growing slowly and an inability to quickly rebound after rapid declines in population size. Bat populations therefore rely on high adult survival rates to compensate for low reproductive rates and prevent declines. Therefore, substantial cumulative impacts of wind-energy development on certain bat species, especially tree-roosting bats, are expected, and these populations would be slow to recover from any population declines (Barclay and Harder, 2003).
Numerous research opportunities exist that pertain to issues such as: (1) identifying the best and worst placement of sites for turbines and (2) mitigation strategies that would minimize impacts to wildlife (birds and bats). Unfortunately, to date, very little research of this type has appeared in the peer-reviewed scientific literature; much of the information exists in the form of unpublished reports and other forms of gray literature. This literature synthesis and annotated bibliography focuses on refereed journal publications and theses about bats and wind-energy development in North America (United States and Canada). Thirty-six publications and eight theses were found, and their key findings were summarized. These publications date from 1996 through 2011, with the bulk of publications appearing from 2007 to present, reflecting the relatively recent conservation concerns about bats and wind energy.
The idea for this Open-File Report formed while organizing a joint U.S. Fish and Wildlife Service/U.S. Geological Survey "Bats and Wind Energy Workshop," on January 25-26, 2012. The purposes of the workshop were to develop a list of research priorities to support decision making concerning bats with respect to siting and operations of wind-energy facilities across the United States. This document was intended to provide background information for the workshop participants on what has been published on bats and wind-energy issues in North America (United States and Canada).