Then again, in terms of direct threats to birds, ignoring climate change, things like powerlines (25 million birds a year in the US), and more significantly air pollution (200-2000 million), windows (2000 million) and cats (1000-4000 million) even very high estimates of 2 million a year including things like habitat destruction and extra powerlines (more direct estimates from collisions are around the 500k mark) from wind turbines make them in turn seem like the lesser of the problems.

Which is not to say it's not an important factor, especially as they affect very specific kind of birds disproportionately, but it's not like wind turbines are primarily bird-killing devices, and it's even possible they may be net benefits to birdkind by, say, reducing air pollution.