Birds, Bats and Natural Habitats

Wind power is widely regarded as a key part of an environmentally sustainable, low-carbon energy future because it is fully renewable and involves near-zero emissions of greenhouse gases. Over the past 20 years, wind power has become the world’s fastest-growing source of electricity.

However, as with all large-scale sources of power generation, wind energy poses its own particular set of environmental challenges. For example, the inevitable visual impacts of large turbines across the landscape are widely recognized and sometimes controversial.

Less widely recognized, but potentially significant, are the adverse impacts that wind power facilities (turbines, new transmission lines, and access roads) can have on biodiversity.

Biodiversity Impacts

Even though wind power development overall might benefit biodiversity by reducing greenhouse gas emissions (thus potentially mitigating global climate change), land-based wind power facilities located in sensitive areas often harm birds, bats, and/or natural habitats.

Birds are killed by collisions with wind turbines as well as with the barely visible guy wires around meteorological towers. Although modern large turbine blades appear to be moving rather slowly when viewed from a distance, the blade tip speed is actually very fast (up to 270 km/hour), so the birds are struck by surprise. For certain species groups, such as large birds of prey, wind turbine mortality could become significant from a conservation standpoint. For example, the 2002-05 installation of 68 wind turbines on the Smola archipelago, Norway (previously designated as an Important Bird Area), caused the breeding population of white-tailed eagles (Haliaeetus albicilla) to collapse, declining from about 19 eagle pairs to only one.

For some scarce, open-country species such as North American prairie grouse, the main conservation threat posed by wind projects is not collisions but rather displacement from their habitat, because the birds instinctively stay far away from wind turbines, transmission towers, and any other tall structures.

Bats tend to be killed by wind turbines at significantly higher rates than birds. The higher mortality for bats is because (a) bats appear to be attracted to rotating wind turbines, rather than simply encountering them by chance and (b) bats can be killed just by closely approaching an operating turbine without even touching it, due to lung damage from rapid decompression. Because bats have low reproductive rates, populations are potentially vulnerable to the added mortality from wind turbines.

Natural habitats can be lost or fragmented when they are cleared to establish wind power facilities, sometimes with significant risks to biodiversity. For example, wooded mountain ridge-tops (particularly in the tropics) often harbor unique plant and animal species, due in part to their wind-swept microclimate. Long rows of turbines with interconnecting roads along such ridge-tops can disproportionately affect scarce, highly localized species. Constructing access roads to previously remote wind farm sites can also lead to the loss or degradation of natural habitats, either (a) directly, through road construction and resulting erosion or (b) indirectly, through increased land clearing, wood cutting, hunting, or other human activities facilitated by the improved access.

Reducing Biodiversity Risks

Various options exist to minimize the adverse biodiversity impacts from wind power. Among the most important of these are project site selection, post-construction monitoring, and (under special circumstances) operational curtailment.

As with other infrastructure development, project site selection is generally the most important tool available for making wind power safer for biodiversity. Where multiple, feasible choices exist for wind power expansion, locating projects away from the most sensitive sites need not reduce overall power generation.

From a biodiversity standpoint, the higher-risk sites for locating wind farms tend to be existing or proposed protected areas, critical natural habitats (including Important Bird Areas), wildlife migration corridors, forests and woodlands, wetlands, shorelines, small islands, native grasslands or shrub-steppes, and sites near caves. Conversely, lower-risk sites tend to have low bird and bat numbers (year-round) and do not harbor species or ecosystems of conservation concern; they include many cultivated lands, non-native pastures, and deserts (away from coastlines and oases).

Once the general site for a new wind farm has been selected, adjusting the location of turbine rows—or even individual turbines—can sometimes minimize biodiversity impacts without significantly compromising power generation or other objectives.

Post-construction monitoring of bird and bat mortality is an essential part of proper environmental management for any wind power project. Monitoring is indispensable for (a) knowing whether or not a significant bird or bat mortality problem exists at any given wind farm, (b) predicting the impacts of scaling up development within a particular wind resource area, (c) supporting adaptive management of wind farm operation to reduce bird or bat mortality, and (d) advancing scientific knowledge. Such monitoring, which involves searching for bird and bat carcasses around turbines, towers, and transmission lines, should be carried out during the first two or so years of wind farm operation and continued if significant mortality is found.

Operational curtailment refers to selected, short-term periods when turbine rotor blades are intentionally kept from rotating. For bats, the most cost-effective type of operational curtailment appears to be a modest increase in cut-in speed, the lowest wind speed at which the rotor blades spin and generate electricity for the grid. Recent, cutting- edge research at wind farms in Canada, Germany, and the United States shows that increasing the cut-in speed from the usual 3.5-4.0 meters/second to about 6 m/s reduces bat mortality by 50-75 percent, while reducing power generation by only about 1 percent. Bats fly around mostly at low wind speeds and mainly at night (and, at higher latitudes, during only part of the year).

For migratory birds, the most useful form of operational curtailment may be short-term shutdowns, in which the rotor blades do not turn during peak migration events. These shutdowns can be cost-effective in preventing large-scale mortality of migratory birds, when species pass through the wind farm area for only a few days or weeks per year. Shutdowns can be scheduled in advance on a precautionary basis to coincide with expected dates of peak bird passage. They can also be on-demand in real time, if radar and/ or human spotters show sizable flocks headed toward the wind farm. This approach has been effectively demonstrated at the World Bank-supported Wind Umbrella (La Venta II) Project in southern Mexico.

New Report—Greening the Wind

A recent World Bank study examined the environmental and social implications of rapidly scaling up wind power development. The study’s technical report, Greening the Wind: Environmental and Social Considerations for Wind Power Development, identifies good practices for managing the biodiversity and other environmental and social issues associated with wind power development and offers practical advice on how best to address these issues in project planning, construction, and operation.

The World Bank Group will continue to collaborate with our clients and development partners in supporting wind power in ways that effectively address environmental and social concerns, thereby optimizing the sustainable development benefits of this renewable energy technology.