Clean-energy wind farms are cropping up rapidly in the United States on rising concerns about greenhouse gas carbon dioxide emissions and flat output of natural gas, which fires most of the power plants built since the 1990s. US wind power is expected to increase by 26 percent in installed generation this year, after similar growth last year.

A study by the National Academy of Sciences released late this week found that wind energy could reduce the energy sector's carbon dioxide emissions by 4.5 percent by 2020.

But federal and state governments should take environmental impacts of wind energy more seriously as part of the planning, locating and regulating turbines, it said.

It said the percentage of birds killed by collisions with the towers and spinning blades of turbines were few compared with kills from vehicles and buildings. But wind turbines could begin to threaten local populations of some bat and bird species, especially along migration corridors, if wind power grows rapidly over the next 20 years, it said.

Audubon supports wind power, believing it reduces global-warming pollution and that any climate change resulting from fossil fuel emissions would kill more birds than wind turbines would. The group cautions, however, that industry-wide safeguards should be developed to minimize bird harm.

The American Wind Energy Association said the industry funds wildlife research through agreements with conservation groups and urged the National Academies to study all energy sources for impacts on wildlife.

REMEMBER ALTAMONT

A wind farm went up at the Altamont Pass Wind Resource Area in California in the 1980s that has killed birds of prey like golden eagles, whose populations are still recovering from use of the now-banned pesticide DDT.

"It's kind of raptor heaven and there's a big wind farm in the middle of it," said Audubon's Daulton. "From our standpoint, the site is particularly bad."

Texas tops the country in installed wind-power capacity where in some areas its power can be cheaper than that from fossil fuel sources. It is also home to the Gulf Coast region, a major flyway for migration of tropical birds.

"I don't envision these wind turbines being like a giant weed eater chopping birds to bits," said Clifford Shackelford, an ornithologist at the Texas Parks and Wildlife Department.

He said bird kills could peak, however, during spring migrations when cool fronts from the North bring late-night storms. "Like any airline, bad weather at night makes it hard for birds to fly, and they use the lights on turbines as beacons in bad weather." He said several species of tanagers, grosbeaks and other birds could suffer, without planning. Turbines more than 200 feet high (61 meters) are often lit so airlines avoid them.