This article on a site called ZME Science has some facts and figures on how many birds are killed (in the U.S., I think) by wind turbines compared to other causes.

• wind turbines: 140,000-680,000 birds per year; 0.3 – 0.4 birds per GW-hr of power production
• power lines: 12-64 million birds per year [Daddy, how can the birds sit on the power lines without being electrocuted? Well, I guess the answer is that the ones you see on the power lines are the ones that didn’t get electrocuted.]
• vehicle collisions: 89 million – 340 million birds per year
• glass buildings: 1 billion birds per year [well, the article says “up to almost”. Rounding is fine with me, but they are oddly precise on some numbers and willing to round on others.]
• cats: 1.3 billion – 4 billion birds per year [I happen to like cats just fine, but if you consider yourself a friend of animals in general it is really kind of immoral and hypocritical to have an unsupervised outdoor cat.]
• fossil fuels: 5.2 birds per GW-hr of power produced “through habitat destruction, mercury poisoning, and acid rain” [presumably, the study referenced here followed some pretty different methods than the ones that looked at birds running into stuff and getting disemboweled by cat claws. But still, you can say this is an order of magnitude more than the wind turbines per unit of energy supplied, controlling for the fact that fossil fuels are supplying more energy in an absolute sense.]

There are some things you can do to make the wind turbines less bad for birds. But really, it’s the cats and the cars and just the general wanton destruction/displacement of nature by our civilization. Now I’ve depressed myself, as I often do.