Hi, welcome to BYC!
I actually don't think it looks like molt. It looks like damaged feathers to me not like dropping feathers.
And not all mites can be seen with the naked eye. Also, red mites live in cracks of wood and not on the bird. So if your are checking during the day you might not be seeing the whole picture.
I would be quite impressed if someone could sex 14 females at 1 month old, unless they were bought at the hatchery.
Upon seeing symptoms.. I do an after dark check with a flashlight, not too early (maybe 2 hours after dark). Place the bird on their back, and bend legs toward chest, keeping it dark so birds stay on roost, part the feathers near the vent and on the abdomen and look for any crawlies running away. if I see anything, I treat with Permethryn spray.
In my experience, hens do not all molt in the fall. I have had several spring and dead of winter molters. The more chickens I have, the more I see that each is an individual and will respond to environmental factors according to however they darn well please regardless of what all the text books say. Also note that things will show symptoms in the weakest of the birds first. Those with stronger immune systems or less stressed may not show signs.
So, There are a couple of suspects that you would go through. You have already eliminated mating damage. That leaves nutrition, pecking, molting (including stress induced), and parasites.
Is your hen still laying eggs? What do you feed (protein %), including treats and supplements? Do you worm? How many birds do you have? Do you know her place in the pecking order? How much space do they have in the coop/run? Do they free range, with how much space? Did you add those 14 one month old chicks in with your flock already?
So basically you can see.. I go down the line and work by a process of elimination.
Depluming mites are one of those microscopic ones. I am seeing evidence of feather damage without evidence of visual parasites in my own flock. So I am gonna take my most calm girl to the vet and see about them doing a skin scrape or microscopic inspection of suspect feathers.. because those need to be specially treated with something systemic, though I don't have all the details figured out yet. A visit to my vet will be $45 plus any tests. With so many birds, I can't afford to mess around. But I don't haphazardly spend either, so I must be taking this seriously. I believe wings and tails is one of the areas evidence shows up first.
Hope you get it figured out.
