Whooping cranes, one of the world's rarest birds, have waged a valiant battle against extinction. But federal officials warn of a new potential threat to the endangered whoopers: wind farms.

Down to as few as 16 in 1941, the gargantuan birds that migrate 2,400 miles each fall from Canada to Texas, thanks to conservation efforts, now number about 266.

But because wind energy, one of the fastest growing sources of renewable energy, has gained such traction, whooping cranes could again be at risk - from either crashing into the towering wind turbines and transmission lines or because of habitat lost to the wind farms.

"Basically you can overlay the strongest, best areas for wind turbine development with the whooping crane migration corridor," said Tom Stehn, whooping crane coordinator for the U.S. Fish and Wildlife Service.

The service estimates as many as 40,000 turbines will be put up in the U.S. section of the whooping cranes' 200-mile wide corridor, which runs roughly from the Northwest Territories in Canada through the Dakotas, Nebraska, Kansas, Oklahoma and Texas.

"Even if they avoid killing the cranes, the wind farms would be taking hundreds of square miles of migration stopover habitat away from the cranes," Stehn said.

The American Wind Energy Association, which says the industry grew in the U.S. by 45 percent in 2007, also says its 1,400 member companies don't want their turbines, power lines, transmission towers and roadways to hurt the cranes, which are protected by the Endangered Species Act and the Migratory Bird Treaty.

"We would hate to see any collisions with whooping cranes," said Laurie Jodziewicz, AWEA's manager of siting policy. "It would be very distressing for everybody."

But Jodziewicz said the wind industry, which is now in 34 states and provided about 1 percent of the nation's energy last year, will continue to grow in the crane's migration corridor and should not be subject to regulations that don't apply to other industries.

"It's a very windy area," she said of the migration corridor. "We certainly want to work toward minimizing impacts, but there is a real driver behind wind energy, which is the need for clean, renewable electricity.

"There are many other things going on in that corridor that could potentially affect that species. So to say that wind development should be stopped while allowing all sorts of other activities to continue, might not be the right course of action."

While Stehn and others say no whooping cranes have been killed by a wind turbine, and they are hopeful the cranes will avoid the wind farms, they remain concerned.

"In the natural world, birds and bats have gotten used to flying around a lot of things," said Nicholas Throckmorton, spokesman for the Fish and Wildlife Service. "But nowhere in the natural world is there a big spinning rotor."

Throckmorton also said the Fish and Wildlife Service lacks the authority to demand that wind developers confer with the agency.

"There are no forced consultations," Throckmorton said. "Other than pointing out that it's illegal to kill endangered species or migrating species."

Concerns about the cranes are not the first for the wind industry, which has taken criticism about its impact on other birds and wildlife, as well as its visual effect on the landscape.

The U.S. Department of the Interior has named a Wind Turbine Advisory Committee to come up with recommendations on how to avoid or minimize impacts to wildlife and habitats from land-based wind farms. The committee includes members of the FWS, wildlife groups and wind energy companies, and was scheduled to have its first public meeting Thursday.

There are three flocks of whooping cranes in North America, with a total of about 525 whooping cranes in the wild and in captivity. But the flock of 266 that migrates through the central U.S. from Wood Buffalo National Park in Canada to the Aransas National Wildlife Refuge in Austwell, Texas, is the only self-sustaining flock. That means it is also the species' best chance for survival, Stehn said.

Whooping cranes, which are about 5 feet tall and have a 7 1/2 foot wing span, normally fly at altitudes of between 500 and 5,000 feet, room enough to clear the turbines, which range in height from about 200 feet to 295 feet, and their blades, with diameters from 230 feet to 295 feet.

The problem, Stehn said, is that the cranes stop every night.

"It's actually the landing and taking off that's problematic," he said. "That's when they're most likely to encounter the turbines and transmission towers."

Stehn said wind farms could also become problematic if they discourage the cranes from stopping in a known area and force them to seek other stopping grounds.

"Will there be food in that area?" Stehn said. "Will there be predators?"

Mary McCann-Gates, spokeswoman for Clipper Windpower Inc., of Carpinteria, Calif., which is building a 2,000-turbine wind farm in central South Dakota in the migration corridor, said in an e-mail that Clipper is aware of the cranes in the project area and "sensitive to any impact the presence of wind turbines might cause."

She also said Clipper "will work closely and cooperatively with USFWS to identify an optimal plan to balance" the project and environmental concerns.

Stehn said it was likely inevitable that whooping cranes would be negatively affected by the wind industry. But he said wind companies could take steps "to make up for the negative."

The most common known cause of death for whooping cranes is crashing into power lines. Stehn said the industry could help by marking its power lines, which run from transmission towers.

"Each crane is precious when you only have 266," he said.