Windmills and Birds

There's an article in nature today about the true cost of wind-turbines to the lives of birds. The conclusion - 3% of a bird per turbine per year, or one dead bird for every thirty or so turbines. They put the avian death toll from wind turbines at no more than 40,000 per year for the USA (the largest wind power producer in the world), compared to hundreds of millions of birds killed by cats. However, there are important limitations to this - mainly that the birds killed by turbines are often bigger, and bigger birds have smaller populations, so the death on an individual is more important.