I'm sure everyone has had this problem at one time or other. One larger chick just won't stop picking on a particular smaller chick. I'm not talking about an occasional peck... I'm talking about a meanie Buff Orp 3 week old pullet that goes after a 2 week old RIR chick with a vengeance. I have 9 total assorted breed chicks from 1 to 3 weeks old. My coop is 10'x12', airy and lots of "toys" and treats and distractions... but this bossy Buff just had it out for that little chick. After considering separating them, which would cause stress among the chicks and be a lot of trouble... I decided I had to try something before there was blood. I filled a spray bottle with water... opened the nozzle all the way so it squirted a hard stream... then sat in a chair in the coop and waited. It didn't take long for meanie Amber to attack little Stella. The instant she started pecking, I blasted her with a couple hard streams of water. She never knew it came from me, across the room. It scared her so bad she ran to the other side of the coop for a minute. After a few minutes, they all got together again, and she started on the chick again.... and got another blast. Really freaked her out. After only 3 times in less than 15 min, that meanie Buff didn't want anything to do with that little chick again. Everytime little Stella came close to her, she ran away! LOL I thought after a day or two, this effect would wear off, but not so.... meanie Amber still associates little Stella with a blast of water and doesn't come near her! I'd be interested in someone else trying this and see if it works for you. You have to be good with your timing... immediate squirt at the instant of pecking.