Missing feathers, lice or mites?

We recently added some new ducks to our flock. They share the coop with the chickens at night (although the chickens stay up on the roosting areas and the ducks stay down below).

I have noticed that some of the chickens are starting to lose feathers on their backs and have some bare patches of skin (see attached photos).

I am worried about them being infested with lice or mites and wondered if there is an easy way to tell. I noticed one of the birds "cleaning" herself where the bare spot it. About 6 of our 30 chickens have this is various stages.

Any suggestions on identification and remediation would be helpful. Thanks!

Have you noticed any of the ducks bullying them?

This is EXACTLY what some of my more submissive hens looked like when they spent more time with my 2 ducks- they had feather loss in those exact places. Unsure why the ducks go for that area- as of right now, 4 out of my 5 hens have some sort of missing or broken feathers from my ducks bullying them. It's does not seem like mating behavior, because the female does it too...more territorial or something. Be careful, because one of my hens had to live inside for the winter because so many feathers were eaten off of her while I was on a vacation!
You can try increasing protein, increasing free range time, etc.... but I did all of that and my ducks still bully my hens. They are getting their own pen built as we speak.

I haven't noticed anything with the ducks. That doesn't mean it isn't happening, but I haven't seen anything. The ducks and chickens are out all day long and all go into the coop at night. Everyone free ranges and the ducks go down to the creek and the chickens go out to the pasture/in the yard (with the exception of one duck that thinks its a chicken).

I will keep an eye on them and see but I didn't know if it was any type of bugs or not.

I house both my ducks and chickens together and have for years. Never had an issue with multiple generations, with the exception of a white crested male duck that fancied two white hens. He thought they belonged to him and would drag them around by the neck. If you coop them up at night together and there is an aggressive duck it wouldn't take you long to spot it. If you want to check for lice it's very easy. They are usually present on lower back just above tail, around vent area, and under neck. The eggs cluster around the base of the feathers and the lice are tiny little oval shaped light brown or cream colored translucent bugs that scatter when you spread the feathers.
This shows both the egg clusters and bugs themselves. Very easy to search for. Just spread feathers around vent, around neck and just above tail. They will infect those places first typically.

Now if you want to check for mites it's also equally simple to check for. Here is a link that explains everything.
http://www.tillysnest.com/2011/06/you-might-have-mites-html/

There are different types of mites, but they are typically small and brown.

Hope some of this info helps!

Thanks!