What medical condition can cause excessive feather grooming and pulling/eating feathers of other chi

So now that my chickens are 5 weeks old, they are in a large yard area and are loving it. Dust bathing, chasing bugs, scratching, eating, looking for grit, napping etc there is one chicken in particular that grooms herself more than others. She is sort of fixated with doing this, even one day she started grooming herself like this in the middle of feeding her egg yolk which she's crazy about and I find grooming herself despite the goodies being offered to her, abnormal. She's also the same chicken that pulls other chick's feathers and eats them causing several chicks to bleed.

She hasn't done the pulling feathers behavior as before now that she is in the yard, just the occasional pecking when in the coop when he goes in, but almost all the time she is in the yard, I catch her grooming herself. I wonder if she is trying to pull out her own feathers or if she is eating her dry flakes of skin. Last time she was on my lap she left several flakes of dry skin or white plumage (she is black, by the way)?

Anyhow, all chicks are on the same feed: organic chick starter with up to 18 percent protein and they are all in the large fenced area. With boredom and overcrowding out of the equation now, why would she be still showing this behavior? and why is she the only one with this problem? Do chickens like dogs develop food allergies or problems absorbing protein or something like that?

Glad to hear she isn't pulling feathers anymore. Chicks go through multiple molts as they grow so some preen more than others. Could be growing feathers bothers her more.

Another cause could be mites, a good dusting with a pyrethrin based poultry dust will work well at getting rid of them.

Have you looked at her skin to see if you notice anything different? Do you see feathers coming in with the sheath still on them? That's usually what the dander if from.

I haven't seen any chickens with allergies but you never know. Do they have a dust bath area? I usually dig a slight hole in a bare spot and they usually start dust bathing.

Chicken feed is a balanced ration made to keep layers in top performance....Or getting young Birds healthy for egg laying age...If feeding treats, egg yolk etc...And free ranging the Birds nutrition is not balanced anymore....

Here are some other reasons for picking...

Too crowded
Too hot
Short of fresh air
Lack of protein or Coop too brightly lit....In some cases once picking starts it's almost impossible to cure...


Best wishes ..


Cheers!

Good news! The pecking has stopped! I still don't know what caused it and what made it stop, but now she's acting totally normal (for over 3 days of close observation!), she's not even grooming herself anymore and today we removed her "tag" from the leg to distinguish her.

Good to hear.