Not uncommon for feather pecking/plucking to start during winter boredom.Hello and welcome to BYC!Glad you joined.
Pictures would be very useful. I can't imagine any external parasite surviving that assault.
We're so happy you've decided to join us 
It's depluming mites! I've dealt with everything else from egg bound to NFM. I've also defeated them all but these.
Glad to be here! Much better than lurking on the sidelinesHi and welcome to BYC
They have access to Sulfur,Neem, DE, and wood ash baths. I think because they burrow, theyWelcome!
I used sulfur powder dusted on the birds and their coop to deal with Northern Fowl Mites. Maybe that will help?
I'm not sure of your application. I have posted this before, the best product to get rid of the mites and lice in my opinion is permethrin which is very cost effective. There are others such as Elector PSP but it is very expensive. I had some birds that were severely infested. I thought they were just molting but weren't getting their feathers back in when I discovered they were loaded with mites. The first thing I tried was DE. The birds weren't improving and still had mites. I first discovered them in only one coop but eventually found them on birds in another coop. I dusted the birds and the coops with the DE and no improvement after treating them for a couple of weeks. Next I did use some sevin dust that I had but it was almost gone but it did help but is no longer approved for use on poultry. I did some research and came up with permethrin. I'm pretty sure the wild birds brought them into their coop. I have used the dust on the birds and use it in their nest boxes and spray inside of the coops everywhere, every crack and crevice, on and under the roosts, ceiling, walls, floors, anywhere the mites can hide. It's best to clean out the coop before you spray. I use pine shavings in my coops. Wear special clothing including a mask and gloves. I did a weekly spraying for awhile, 3 or 4 weeks and put permethrin poultry dust in the nest boxes, originally sprayed the birds getting under the wings and worked it through their feathers with gloves which you can also do with the dust. Slowly the birds began to recover and get their feathers back in. I think if I hadn't treated with the permethrin when I did I probably would have lost some birds to the mites. The birds were in bad condition. Permethrin only kill live pests, not the pests eggs so repeat treatments are necessary. TSC as well as most feed stores carry the permethrin powder, premixed spray bottles and the concentrate. I used the concentrate. It did not affect the birds but I did keep them out of the coops while it dried. I spray my coops as needed and when I spray I do weekly spraying for 3 or 4 weeks then stop as I don't want the pests to develop a resistance to the permethrin. Repeated weekly spraying is necessary because again, it does not kill the mite eggs and as an added benefit is there is no egg withdrawal period so the eggs are safe to eat. The birds are beautiful again. In my opinion Permethrin works great. Good luck...
