TAZEWELL, Va. — Wind turbines offer a clean energy source, but they share the air with birds, bats and other fliers that may have problems coping with what is — to them — a new and unexpected obstacle.

Dominion and BP Wind Energy North America, Inc. have proposed building a large windmill project along East River Mountain near Bluefield, Va. Aside from questions about potential noise and impact on property values, some members of the public have had questions about how the structures — up to 400 feet tall — would affect the many birds and other flying creatures found in the region.

Wendy Perrone, executive director of the Three Rivers Avian Center in Brooks, W.Va., said Friday that she had not seen all the details about the project, but there are some concerns.

“The mountain range is a migration route used for many decades and centuries....from butterflies to bats up to and including eagles,” she said.

Windmill projects have a potential for killing bats. Why this happens is not yet clear, Perrone said.

“Bats are really seemingly killed in massive numbers,” she said.

There are theories about why bats die near windmills. Some studies show bats going behind windmill blades and getting caught up in their wake. A drop in air pressure caused by the blades’ passage may give bats a decompression problem similar to “the bends” experienced by scuba divers, Perrone said.

“The question is finding a solution. Everybody is pushing to find out why this is happening,” she said.

The journal “New Scientist,” an online publication, recently published an article about the bat and windmill connection.

“It’s fascinating sort of stuff,” Perrone said. “It’s very hard at times to come up with an absolutely perfect energy solution.”

How windmills could impact birds is another question.

“There’s a lot of that (information,) she said. “All you have to do is go to Google and you’ll be inundated. Some of them (problems) have been figured out and improved on.”

Early wind turbine designs had lattice towers which provided plenty of roosts for birds; raptors using them as perches to watch for prey could fly off and be struck the blades. Modern designs address that issue, but there are others to consider, Perrone said. If bats can be affected by windmills, there may be ways native birds could be affected, too.

The center’s directors have agreed that energy needs must be addressed.

“We know the nation’s energy needs are not going to be met wholly with reductions in use, so we support developing and using renewable energy sources such as wind, solar, geothermal and others with the caveat that any negative impact be fully addressed and minimized,” Perrone said.

One possible way to minimize potential impact is to turn off windmill blades during peak migrations, she said. This shutdown would be only for a brief period.

“Two or three days, tops,” Perrone said. “In the grand scheme of things it’s not a big change. It could save a lot of birds and bats.”

Another issue is the windmills’ lighting. Migrating birds that rely on stars could be drawn toward the towers.

“That is easily remedied by turning the lights off,” Perrone said. If lights are needed so the towers won’t be an obstacle to aircraft, red lights — which do not affect birds as much — could be used instead of white lights.

The region is “a very rich area for birds,” Perrone said. Both bald eagles and golden eagles have been sighted in places like East River Mountain.

“Eagles, osprey, harriers, a whole slew of raptors and a whole slew of song birds,” she said.

— Contact Greg Jordan at gjordan@bdtonline.com