The windmills are coming; the windmills are coming!
Seriously, though, I suspect all that thrashing around of propeller blades disturbs the night-time temperature inversion effect near the ground, especially in low humidity environments. The pointy headed Gummn’t PhD welfare pimps know that, but why let details get in the way of a nice fat study grant.
I would think the blades ain't turnin' unless the air is ALREADY moving enough to disturb this inversion layer.