More than 60 years after it was pushed to the edge of extinction, one of North America's rarest birds, the whooping crane, faces new danger from environmentally-friendly wind farms, conservationists warned.

"Companies want to put their farms where the best wind is, and that overlaps with the migration corridor of the whooping crane," Tom Stehn, the whooping crane coordinator of the US Fish and Wildlife Service, told AFP.

"There are areas where we know large numbers of whooping cranes stop (during migration) and we would like wind companies to avoid those areas, with a good buffer zone," Stehn said on the eve of a key business-to-government conference on renewable energy, the three-day Washington International Renewable Energy Conference (WIREC).

The majestic whooping crane, which stands around five feet (1.5 meters) tall, was pushed to within 15 birds of extinction last century.

Since 1941, conservation groups have painstakingly built the whooping crane population back up to around 360 in the wild and 150 in captivity.

Whooping cranes migrate annually between wetlands on the coast of Texas and the Northwest Territories in Canada, flying a route that corresponds to the corridor wind companies are eying for their huge turbines as their industry expands.

That expansion was given a boost last week when the US House of Representatives voted to extend tax incentives for developers of the renewable power source.

Non-profit organization Audubon, a nature conservancy group with a focus on birds, also urged that wind energy not be allowed to develop unchecked.

"We're very much in favor of wind power because we're so concerned about the other sources of energy that are contributing to global warming," said Greg Butcher, Audubon's director of bird conservation.

"The trick is to get the siting and the design of the turbines right so that big birds like the whooping crane can avoid collisions," he said.

Of greater concern than collisions with turbines was the reduction of natural habitat of the whooping crane and other birds found only in North America, said Butcher and Stehn.

Loss of natural habitat was key in nearly driving the whooping crane to extinction, said Stehn.

If the wind industry is allowed to develop unchecked in the grasslands of the US Midwest, other animal species would suffer significant habitat loss and could be in danger.

One such species, according to Butcher, is the prairie chicken, which will not nest near tall structures such as wind turbines.

One subspecies of the prairie chicken, the heath hen, is already extinct; another, Attwater's prairie chicken, is endangered.

Laurie Jodziewicz, a spokeswoman for the American Wind Energy Association (AWEA), said the renewable energy industry was aware of the threat to bird species of wind development, and has engaged environmental groups, government agencies and academics in talks to seek ways to expand production without harming wildlife.

"We have an ongoing research program that focusses on prairie chickens but we are also looking at other grassland bird species to understand the different kinds of impact that development might have," Jodziewicz said.

"But it's important to remember that wind development is not the only thing that is causing habitat loss," she said.

"Wind development probably pales into insignificance compared to oil and gas, and town development."

Stehn aired concern about how wind development will result in "more and more powerlines" and urged that they be well marked to minimize the number of birds that collide with them and die.

Wind energy provided electricity to one percent of US homes last year and is projected to grow by 25 percent annually, with most of the expansion planned for the breezy corridor that stretches from Texas to Canada, according to the AWEA.

"They have to tap into the best wind resources," said Stehn.

"They can't take areas where the wind isn't going to blow every day -- it's not economically feasible."