I own chickens and have had a bullying problem in the past. In the winter they have a lot less space and they get bored and stressed easily. The hen that took the “rooster”/protector role started pecking the smallest and sweetest chicken and drew blood. I had to keep the small chicken isolated from the flock for a few weeks while its wounds healed and put special goggles on the bully chicken for a month- they prevent it from seeing in front of itself so it forgets what’s there after a few seconds. Yeah they can be vicious, but it’s definitely preventable if they’re raised right instead of at a factory farm.