Advances in wind turbine technology and increased interest in renewable energy sources have led to a rapid expansion of the wind energy industry in the United States. A wind turbine is a device that converts kinetic energy from the wind (also called wind energy) into mechanical energy. This process produces wind power. If the mechanical energy is used to produce electricity, the device may be called a wind turbine or wind power plant.
Wind turbines are manufactured in a wide range of vertical and horizontal axis types. The smallest turbines are used for applications such as charging batteries or for auxiliary power on boats. Large grid-connected arrays of turbines are becoming an increasingly important source of wind power-produced commercial electricity.
Studies have documented that wind energy facilities kill birds and bats. Mortality rates vary among facilities and across regions. Studies indicate that relatively low raptor fatality rates are found at most modern wind energy developments with the exception of some facilities in California and Wyoming. Turbine-related bat deaths have been reported at each wind facility, and studies generally indicate lower bat fatality rates at facilities in the West than in the East. There is still much uncertainty regarding geographic distribution and causes of bat fatalities.
Most birds killed at wind turbines are song birds. Migratory songbirds often migrate during the night at altitudes generally above rotor swept areas when weather conditions are favorable. Risk may be greatest during take-off and landing where wind facilities abut stopover sites. Studies have indicated that the level of bird use at the site and the behavior of the birds at the site are important factors to consider when assessing potential risk. For example, raptor fatalities appear to increase as raptor abundance increases. Certain species – including red-tailed hawks (Buteo jamaicensis) and golden eagles (Aquila chrysaetos) – that forage for prey in close proximity to turbines appear to have increased fatalities, while others like common ravens appear to avoid collisions with turbines.
All studies of bat impacts have demonstrated that fatalities peak in late summer and early fall, coinciding with the migration of many species. Bat fatalities also occur during spring migration for some species at some facilities. Several species of bats are vulnerable to collisions with turbines. Three migratory tree-roosting species seem to be particularly vulnerable: the hoary bat (Lasiurus cinereus), Eastern red bat (Lasiurus borealis), and silver-haired bat (Lasionycteris noctivagans).
There is also evidence that ground nesting birds, such as prairie-chickens and sage grouse, may avoid areas with wind turbines. It is believed that they avoid structures that could be used as perches for predators such as raptors. Turbine strings or arrays may also affect the habitat, causing the birds to search for less disturbed habitat. This can disrupt their breeding and nesting behaviors, resulting in fewer chicks surviving to adulthood.
Get information on efforts to reduce impacts of wind facilities on birds and bats.
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Download the Land-based Wind Energy Guidelines.
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