My school, 20+ years ago had a huge glass side (possibly still does) that at just the right time of day was utterly indistinguishable from the sky to the human eye.
I sat in many an assembly to the huge "thud" of birds flying into it at full speed. The school never did anything about it in the time I was there.
This was one school with some 20-30m wide windows, imagine just a single building with an order of magnitude more glass.
The glass balcony of the flat I used to live in caused issues for birds, I imagine glass is a much, much larger issue than wind turbines given its prevalence.