That number is completely dwarfed by the number of birds killed annually by pet cats, cars, power lines, the airline industry (mostly airports culling birds), cell towers, hunting and, wait for it, fossil fuel powerplants. Per GWh a fossil powerplant kills about ten times as many birds as a wind farm.
Saying wind farms in the US kill half a million birds sounds impressive until you see that collisions with buildings are estimated to kill between 100 million and one billion birds every year in the US.