I dig your ideas and and stance on looking for a solution. I don't think windmills go fast enough to achieve that effect, though just blinking LED strips might do the trick. I'm no bird lawyer per se, but I do believe their sight is different to ours.
You got my fantasy going, so now I'm imagining the windmills spouting some artificial clouds into the wind and lasers displaying birds of prey into the mist.
Without any googling whatsoever I am pretty sure there have been studies on the matter. My guess is either there is no trivial solution or something that would go against efficiency.
There is definitely a big alternative wind energy movement about. I've seen designs on small scale that basically just wobble and generate power. Maybe we have to step back a bit, before we can go full in. We can't have slowly rotating blades chop up our birdies.