Feather mites i think are a seperate pest the correct common name of the pest that I feel we are discussing is de-pluming mites. These mites are microscopic and result in the bird pulling its own plumage out because of the discomfort they produce. At least in advanced cases there is normally reding of the skin that accompanies de-pluming mite infestations.
Here is the scientific name.
This mite is a burrowing mite and that makes it related to the scaly leg mite and i hope that you'll know how small or hard to see scaly leg mites are.
I suspect quite often that the rooster bears the blame for the damage done by De-pluming mites.
If you wish to do a visual check for de-pluming mites then you may need an electron microscope. I suspect that they are about as big as the dust mites in our beds, or the eyelash mites living in your eyes or mine.
I also feel that de-pluming mites are much like the mite that causes mange in dogs.
If you study the above photo it looks to me like the poor hen in the picture has been pulling on the ends of her tail feathers but that there is little or no damage to her plumage in areas that she can't reach with her own bill.
Edited by chickengeorgeto - 1/21/16 at 1:10pm