How do I get this aggressive chick under control?

[CoolChickenPerson]

Rasing my baby chickens have been a breeze so far, my weak chick recovered, everybody is healthy, but I've recently came to a problem. My oldest chick (about 5-6 weeks old) has become aggressive, it pecks the backs and pulls the feathers of the other chicks, how do I correct this behavior?

 

[rosemarythyme]

How many chicks and what are the ages? How large is the brooder and are they getting any outdoor time? Are you using a heat lamp or do they get a true day/night cycle? Boredom is a possibility, or it could be a reaction to being kept up all the time if you're using a heat lamp or additional artificial light.

 

[LaFleche]

Please upload a few pictures of your current brooder situation for us to better assess where the problem might stem from.