I have 17 chickens and when I went in the run a couple weeks ago I noticed a small part of the run was covered in feathers!!!! Not wing or tail feathers....like the feathers under their wings(the real small and soft, fluffy ones).....not sure what they are called. But they were all over the ground. All the chickens seem healthy and happy. My run is HUGE so they are not crammed. I have never seen them pull feathers out of each other.....but when the "preen" themselves they pull out 1 or 2 small fluffy feathers near there butt lol. Why do they do this? Is this normal/ok? I'm new to chickens so I am not sure if what they are doing is just "chicken stuff" or bad. They are a little over 2 months old and are Brahmas and Buff Orphingtons.