I had this issue last week. Same thing...one chick with all it's tail feathers missing, a raw tail and it was also picking at itself. I tried to isolate it and find the culprits. I thought I"d found the culprits, isolated them too but actually, I'm not even sure if it was the two I isolated. At the time, there was a lot of light down (not actual feather) pecking going on and it seemed like it was 2 SS in particular.
My brooder was big enough, I use a red light and no bright lights except natural lighting and an overhead light and I've started actually turning off the red light at night if I can keep the RV they're in warm enough. I turn on a light in other spot in the RV so that it's not pitch black. I was worried about over-stimulating them as well.
Then a few days later I found another one with one tail feather missing and a little blood.
I've been using blue-kote on them and they're fine now. I put pine tar salve one the worst one and the other chicks really hated it, as well as the chick itself that was pecking at itself. The first was a week ago and the other four days or so ago.
A couple things may have contributed to my issue. One, a couple days before it happened my brooder had been too hot and I lost one chick because of it. Stress happened right there. At the same time, I'd been giving them high-starch treats which I feel were displacing some protein. (oatmeal and cooked rice) Then the day before I'd bumped them up to a bigger brooder with pine shavings for litter (they had been on shredded paper previously). So, a lot of stress, new litter (which they were eating and probably displacing protein as well)
THEN I'd also changed to a new lower protein crumble. From 20% down to 18%. I did it very gradually but I honestly think, with all the signs above, that the lower protein all the way around caused it with the possibility of the heat stress and too much bright light at night.
I started giving them chopped boiled eggs every evening (two eggs for 29 chicks) and also half a can of tuna mixed with that, a little greek yogurt and I eliminated the starchy treats. I only give them some dandelion greens/grass/spinach sprinkled in the litter in the morning before I go to work to keep them busy mostly. My "theory" was that they'd fill their crops with pure protein at night although I have zero clue whether it's more effective that way or not
So far, so good for me. I put the injured first chick back in after a day. It wasn't eating by itself and was beating itself up trying to get to the other chicks (it could see them) I kept putting on the blue-kote and pine tar at least twice a day and they left it alone. It was dumpy and a bit scared but it's recovered well, although I can tell it's definitely at the bottom of the peck order.
Isolating the other two SS I thought were the culprits did nothing after a couple days. It wasn't long enough, I know but they're fine now. I considered brooding all the "busier" Speckled Sussex by themselves but I kind of think the Barred Rocks were also in on it.
The two chicks that got beat up were both Buff Orpingtons...they're much more timid than my other chick breeds and I"ve read that they can sometimes get bullied a bit in a mixed flock. They're getting a little more confident now at 16 days old. Still, I come home every night and go out in the mornings worrying I"m going to see blood! It took me about 10 minutes of standing there staring at them before I even saw the second chick had an issue.
These are lighter chicks and you can see some blood in their new feathers...hate that!
Good luck and I"d definitely try some high-protein snacks for now. Tuna especially! The second incident happened even when I was giving egg so I bumped it up more with the canned tuna (light albacore in water...drained out most of the water and mixed with the chopped egg) They FREAK OUT over the tuna...scary mad insane rush!!! The very second they smelled it they went nuts.
When my chicks were about 2 weeks old, they all ganged up on the smallest, a RSL named Penny. When I found her, her entire bum feathers were pecked out and she was bleesding. I cleaned her up and seperated her. Well, later that night, she got back with them and they haven't bugged her since. I didn't use bluekote. I used Rooster Booster on her bum. A few tried to peck her again, and it was gratifying to see them freak out because of the taste. lol Now they are picking on a MUCH bigger chick. A 6 week old EE named Holly. Mostly its my BR, Yoshi. She's decided that she is the cool chick and Holly is the nerd.. or something.
