What’s 3% of a bird? The last seven centi metres of a swan’s wingspan? The right foot of an ostrich? Or the annual death toll attributable to an average wind turbine? In the context of last week’s report1 by the US National Academy of Sciences (NAS) on the environmental impacts of wind-energy projects, it’s the third definition that counts. It takes 30-odd turbines to reach a kill-rate of one bird a year.
The scientists who wrote the report naturally attached lots of caveats to this figure, which they gleaned from 14 studies they felt were of good quality. They acknowledged that rates can differ widely from site to site, and that although, as Hamlet said, there is a special providence in the fall of a sparrow, such a fall might not be quite as special, or worth avoiding, as the death of a bald eagle.
In the final analysis, though, whichever way you slice it, or them, America’s birds seem to die in turbine blades at a rate no higher than 40,000 a year. Deaths due to domestic cats, on the other hand, are put at “hundreds of millions”. It is possible, the panel noted, that the turbines are rather worse for bats; recent studies have turned up more of their carcasses than expected. But the numbers are still small.