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Officials from the US Fish and Wildlife Service are concerned about whether migrating whooping cranes, an endangered bird species, are at risk from wind turbines. Each winter, the world's only free living, naturally reproducing flock of whooping cranes journeys 2500 miles from its breeding grounds in Canada to the warmer climes of the Texas Gulf Coast. The migration cuts a 200-mile wide swathe through the central United States, a corridor that also contains some of the best wind energy resources in the country and where Texas billionaire oilman T. Boone Pickens is pushing a plan to build 200 GW of wind power plant.

It is not clear what threat wind farms pose to whooping cranes, reports Karl Kosciuch of TetraTech EC, as there have been no documented cases of the birds flying into turbines. But there have been 44 whooping crane deaths in collisions with power lines since 1956. Although the birds typically fly at heights of 180-300 metres when migrating, above the tallest turbines, problems may come about during landing and take-off.

"When they land to feed and sleep they make low flight patterns between these areas," says Kosciuch. This is at heights of ten to 20 metres, "which puts them right in the zone of collision with overhead distribution lines and transmission lines."

Another concern "that is not really supported by data at this time" is the impact of wind farm development on the availability of stopover habitat, said Kosciuch. Whooping cranes roost primarily in wetlands and feed in upland crop stubble -- and they like the two to be in fairly close proximity. "If a wind energy facility is developed in the Midwest, say North Dakota, will whooping cranes avoid stopping at or near that area, thus effectively leading to habitat loss, even though there might still be wetlands on the ground?" asks Kosciuch.

In April, the US Department of Interior provided a $1.1 million grant to nine states within the corridor to help develop a habitat conservation plan for North Dakota, South Dakota, Montana, Nebraska, Kansas, Oklahoma, New Mexico, Colorado and Texas "to avoid and minimise impacts" from wind energy development. The plan will also examine ways to mitigate impacts on the lesser prairie chicken. A number of wind developers are participating in the study.

Whooping cranes are protected under the federal Endangered Species Act, which makes it illegal to kill them. There are an estimated 247 individual birds living in the wild, up from a low of 14 in 1938.