The windmills don't have to strike a bird to kill it. In Europe a migratory bat is also being killed by windmills. The bats evade the blades by echo location but there is a pressure front followed by vacuum. This may be exacerbated nearer blades and nearer the tips. The wave of pressure-vacuum are said to burst blood vessels around the heart. The bats crumple just after passing the windmill. In daylight. I imagine most birds avoid windmills but its going to kill some that take chances.

Song birds are in severe decline in North America. Some could go extinct in our lifetimes but probably many will in our children and grandchildren's lifetimes if we do not find a way to reverse the tide.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers