Mortality Threats to Birds - Wind Turbines

Background

Wind energy is one of the lowest-priced renewable energy technologies available today, costing between 4 and 6 cents per kilowatt-hour, depending upon the wind resource and project financing of the particular project. Wind power is also the fastest growing of the renewable energy technologies. Global capacity increased from 2,500 MW in 1992 to just over 40,000 MW at the end of 2003 - an annual growth rate of near 30%. Airflows can be used to run wind turbines and some are capable of producing 5 MW of power. Turbines with rated output of 1.5-3 MW have become the most common for commercial use. The power output of a turbine is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically.

Globally, the long-term technical potential of wind energy is believed to be 40 times the current electricity demand. To realize this potential could require large amounts of land to be utilized for wind turbines, particularly in windy areas. Offshore sites experience mean wind speeds that are ~90% greater than those on land, and so could contribute substantially more energy. This number could also increase with higher altitude ground-based or airborne wind turbines.

Impact on Birds

Wind energy production affect birds primarily through direct mortality from collisions with the turbine blades, towers, power lines, or with other related structures, and electrocution on power lines. Secondary impacts on birds also includes avoidance of the wind turbines and habitat surrounding them and impacts resulting from the affects on bird habitats from the turbines’ footprint, roads, power lines, and auxiliary buildings.

Recent U.S. studies indicate that bird mortality at wind turbine projects varies from less than one bird/turbine/year to as high as 7.5 birds/per turbine/year. This means that between 10,000 and 40,000 birds may be killed each year at wind farms across the country - about 80% of which are songbirds, and 10% may be birds of prey. While not a large figure, local or regional impacts may be significant, and the rate of increase in turbine construction has conservationists concerned that new generators be built to standards that minimize the potential for bird kills. Bats are also subject to high mortality at wind farms frequently at considerably higher rates than birds.

The Solution

The increasing number of proposals for new projects has stimulated discussion on the need for proper siting, operation, and monitoring guidelines or regulations to prevent, or at least keep to a minimum, avian and bat mortality.

Very careful consideration must be given to each site for wind turbine projects. Each state should adopt guidelines or regulations to assure the prevention or minimization of avian impacts from new wind turbine construction and operation (see guidelines for Kansas and Washington). Comprehensive voluntary guidelines for siting, operating, and preventing/minimizing avian and other wildlife impacts have been issued by the U.S. Fish and Wildlife Service.

Before construction of new wind farms, detailed studies should be conducted to assess the potential impact on birds, bats, and other wildlife. Sites known to be used by birds and bats listed under the Endangered Species Act should be avoided if the construction and operation of wind plants might adversely affect these species, as should locating turbines in known local bird migration pathways, in areas where birds are highly concentrated, or in areas or landscape features known to attract large numbers of raptors.

Further Resources

American Bird Conservancy's policy statement on birds and wind turbines.

U.S. Fish and Wildlife Service Guidelines for the siting and construction of wind turbines

Washington State guidelines for the siting and construction of wind turbines

Siting Guidelines for Windpower Projects in Kansas

Documented wind turbine studies by West Inc

The National Wind Coordinating Committee

U.S. Fish and Wildlife Division of Habitat and Resource Conservation

National Wind Technology Center