BANGOR (AP) – The possibility that the 400-foot-high turbines of the state’s first wind farm could kill birds and bats has stalled the project in central Aroostook County.

Maine Audubon last week appealed the state Department of Environmental Protection’s approval of the plan by Evergreen Wind Power LLC to construct 33 turbines atop Mars Hill Mountain.

Maine Audubon has expressed concern that the 50-megawatt project, which can provide clean, renewable power to 25,000 homes, could be harmful to migrating birds.

“We’re excited about the potential for wind power in the state – the majority of wind farms don’t cause problems. But when they do, they cause big problems,” said Jody Jones, a wildlife biologist with Maine Audubon.

Wind currents that make mountainous areas good wind resources also serve as highways for most migratory birds. Thermal updrafts, particularly on the northwest side of small mountains, are used by hunting raptors, like hawks and eagles, that glide on the winds.

Biologists don’t know that Mars Hill Mountain is in a migratory corridor. Most scientists assume that birds migrating through New England probably follow the coastline, far east of Mars Hill, but the research has never been done.

“We just don’t know what’s happening in the interior of Maine,” Jones said.

General surveys conducted by local birders indicate that more than 70 species of birds, including federally protected bald eagles and state-protected golden eagles and peregrine falcons, have been seen near Mars Hill Mountain.

Federal biologists were concerned enough about the potential risk in Mars Hill to propose at least three full years of pre-construction study before the turbines are constructed, according to a letter from Gordon Russell, supervisor at the U.S. Fish and Wildlife field office in Old Town.

“In the absence of adequate pre-construction data on migratory bird usage of the airspace at the proposed turbine site, Evergreen Windpower proceeds with this project at its own risk,” the letter reads. “There is a liability there,” Russell said.

The turbines in Mars Hill simply pose the lowest possible risk to birds because of their slowly rotating blades and streamlined design, the project’s supporters said.

“These are not bird-killers,” said Pete Didisheim of the Natural Resources Council of Maine, a wind power advocate.

Evergreen has promised to do what it can to reduce the risk. But over the past five years, a new controversy has emerged as biologists realized that bats were also being killed by turbines.

“We don’t know exactly what’s happening with bats. They’re flying around and they’re coming too close, and they’re getting whacked,” said Richard Hoppe, a state wildlife biologist based in Aroostook County.

Northern Maine may have as many as five resident bat species, and information about their lives is even harder to come by than bird data.

Peter Gish of UPC Wind Partners, Evergreen’s parent company, said Audubon is calling for an “unfair standard” for wind turbines as compared to other types of development.

“This is already a developed site, with a ski area, and ATV trails, and six cell towers – some taller than the turbines are going to be,” Gish said. “There is no evidence whatsoever that this is a migratory bird path.”

The state Department of Inland Fisheries & Wildlife had recommended further study before allowing the turbines to be built.

Ultimately, the state agreed to the project in exchange for Evergreen’s promise to do after-the-fact studies for one year and to address any problems with solutions like shutting down turbines during sensitive times or adjusting lighting.