Never thought about it, but that's a great point and comparison. From quick Google search: 365 million and 988 million birds die every year from window collisions (that's US alone). Windmills/turbines: 140,000 and 679,000. Then if you do per windmill vs. per building obviously the windmills are going to "win," but it's the absolute that would seem to matter in this case.

As you said, that has nothing to do with the actual preference for fossils vs. turbines, but a great point nonetheless.