That's a red herring. The danger to birds has been shown to be almost negligible when compared to other concrete structures, cars, cats etc. Birds will get killed by a lot of things, it's not reasonable to draw the line at this point.
They predict that it will increase into the tens of millions, as more windmills are constructed.
Perhaps that number is "negligible" in a relative sense, but why kill birds at all? We should be working to increase the bird population, not adding more ways to kill them.
I'm not an expert, but just a bit of web searching has turned up some alarming studies and predictions. Maybe they're exaggerated; maybe they're one-sided. But it seems to me the problem shouldn't just be dismissed out of hand.
Birds eat ticks and other pests. 50 years ago, flocks of birds were much larger. Huge swarms of birds would descend on a pasture or a green grass yard and pretty much eat all the bugs. This is a beneficial thing.
Stopping wind power expansion because of the birds that die in collisions is like not extinguishing a building on fire because of fears of the damage the water will do to the building.
That said, many laws include provisions to minimise the harm to birds and bats. Including the German one under discussion.