That's good that u sprayed for mice

Like
@Ridgerunner said it could be roost mites maybe or some other sort of pest. You would think that mice would attract your chickens

My chickens would probably want to be in their coop more so that they could eat the mice. I hope your hen is okay with the bloody beak

I wonder how it happened? The cloth should help. Every winter we put a tarp up on one side of the run, and it blocks the wind

Of course, happy to help

Sorry that I didn't really know what was causing your chickens to roost outside