Fossil fuels also kill millions of animals every year (not just birds), and harm the health of humans. Even ignoring the long-term effects of CO2, fine particulates cause respiratory problems, higher blood pressure, and can cause cancer. The tricky bit is you can draw a straight line from the burning of coal to any particular (heh heh) death, it is just a statistical shift in health outcomes.

Anyway, all of that absolutely dwarf the birds getting killed by wind farms.

Also, it turns out that bird flight patterns are very stable from year to year, so they study flight patterns, and place the windmills out of the way.