Help, 5 week old chick pulling out other chicks feathers

We have 4 chicks that are 5-6 weeks old. Today I noticed one of them (a white leghorn), who already seems to be the most dominant of them all, picking at feathers out of the chest of our creme legbar. Later she seems to be picking at feathers on the CL's vent area. I immediately panicked after reading online about cannibalism. The CL does not seem at all bothered by the leghorn doing this but it is very bothersome to me. My concern is the other chickies learning this behavior as well.

Here are additional details:We just increased the brooder size to 4 x 2 x 2 about a week ago. There are several roosts in the brooder and the temp is around 70-75 degrees. We will be removing the heat source this week in preparation for the transition outside. It is a a red heat bulb so I do not think it is stress from too much bright light. We are not ready to move them outside yet due to the excessive snow and low temperatures. They are being fed a starter feed with 18% protein. I have read some things that say protein should be 20% - could this be the issue? Aside from changing the brooder about a week ago there have been no other changes.

I am concerned about this new behavior. I have read conflicting info. Some say to remove and cull ithe picker mmediately. Others have offered some possible solutions. While I would like nothing more than to attempt these solutions I am scared of putting the rest of the flock at risk of picking this up and it becoming an even bigger problem.

Thank you in advance for suggestions.

That's kind of a transition age for protein. First, I'd give them some tuna or mackerel for a couple days and see if that fixes it.
I went from 20 % to 16 at about 8 weeks once and had cannibalism I thought was rats.

Another thing is that I no longer use a light source for brooding. I use ceramic emitters and give 8 hours of dark at night.
If they're indoors, try removing the light now and see if they huddle together during the day. If not, they no longer need heat.

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I will try the tuna. I know they LOVE it. I will give it a couple days and see if it helps. Glad to hear my instincts may be on the right track......

Common sense is a valuable thing and not that common.
When I had the cannibalism thing last year (which I had never seen in my life of chickens) I bumped the protein back to 20% for a couple weeks and never had a problem again. I use a 16% protein organic grower for all my birds and adjust the protein for needs with a 60% protein fishmeal. Mixing the two at a 10:1 ratio nets 20% protein.

ETA
The reason I suggest canned mackerel is that it is very cheap. Per ounce it's about half or a third the cost of tuna.
Most people have tuna in the cupboard though.

Fish is around 60+ % protein so it doesn't take much to make a difference.
Other meat or meat scraps will work too. Beef, pork, chicken, turkey, etc..

Make sure they have grit if feeding anything other than chicken crumble, pellets or mash..... you probably know that, but just sayin.

Space might also still be an issue, 4' x 2' might be tight for four 6 week birds.
If it's warm enough during the day, maybe an outing in a day pen would help....or the coop if it's empty of other birds.

Yes, I knew about grit. Thanks though, still have much to learn!

I wondered about size of brooder as well. We kinda "adopted" the 4th bird so I hadnt planned on needing more room inside. It is also usually much warmer by now here so Inhad anticipated them moving outside right around now.

I will see what I can do to expand the brooder. I'm crafty!!

I use large moving boxes from Lowe's at about $1.50 each. I put them side by side when I can't get the chicks out in a timely manner and cut doorways between them. Keep the heat in one and water/feed in other 'rooms'.

x2 on the Lowe's boxes...those work really well...and I agree with the increase in protein and the increase in space...boredom creates a lot of stress issues which is often released through picking.
LofMc

Give them a container with some dirt to play in. Picking often starts with boredom.

Besides the protein issue, boredom is the second most common cause of feather picking. And you are right to be concerned. The behavior can be learned and become epidemic.

If this continues after you feed the tuna/mackerel and provide for additional exercise space for part of the day, I would try removing the feather picker during the warmest part of the day. Take this chick out of the picture for a period of time, say each afternoon before bedtime, then put her back when it's time to go to sleep. (Yes she'll complain loudly, but she won't die from it.)

Sometimes you can short circuit behavior with a small social interruption.

It is also correctly recommended that you provide a dark period each night. I do this from the beginning to establish day and night rhythms and to relieve stress from too much light. If you still need the heat at night, drape a dark cloth over the brooder between it and the light.