Natural beats artificial? According to a study released by the U.S. National Academy of Sciences, at least 40, 000 birds in North America die every year due to striking electricity-generating wind turbines. The figure is further broken down to the estimate that it takes around 30 turbines to kill one bird every year.

In comparison, bird deaths due to the domestic house cat have been attributed to figures in the hundreds of millions.

Similar studies conducted in Europe seem to point at similar figures, with a published report in Spain - the third largest wind power-producer in the world - indicating similarly low bird deaths attributed to their turbines.

But while these reports indicate a gradual debunking of the strongly held belief that wind turbines are a major cause of avian death, environmentalists from Europe don't appear to be thoroughly convinced.

"My personal opinion is that the evidence base is very poor," says Andrew Pullin head of the Birmingham, UK-based Centre for Evidence-Based Conservation regarding the US report.

Spanish environmentalist Alvaro Camiña, who monitors 70 of his home country's 140 wind farms comments that the numbers don't provide for all important details. He states the case of the griffon vulture: "It's important to know the mortality of large birds because they have a lower number of offspring. Even a small number of deaths can affect a population."

On the other side of the fence, wind turbine-dependent power firms assert that the bird deaths attributed to their machinery is  taken out of context. "I heard that over 1,000 birds a year run into the Washington Monument. Should we tear that down?" said PowerWorks president Rich Koebbe regarding the matter. "We're out here trying to do a job to save the Earth. We even save birds, since they are twice as vulnerable to pollution as humans."