Correct. The pecking order is in play from day one and is ongoing. You will notice one giving another a swift peck on the back as she passes by. That's one way they affirm their rank among each other. Sometimes, a lower rank hen will challenge one just above, and there might be a very brief altercation that is over so quickly you never see it take place. But in a few brief seconds, the pecking order just changed. It rarely involves prolonged fighting.
Are you sure you want to bring a rooster into this flock of peaceful pullets? Unless you want fertilized eggs, a rooster will upset the order, annoy and harass the pullets, and if you want a "guard" for the chickens, get a dog or llama. Roosters are just as vulnerable to attack as hens. In fact, the pullets will usually have one among them who is already assuming the role as "lookout" and will warn the rest of danger. Beyond that, it's a very, very rare roo that can fight off a predator, and he usually dies in the process.
