so when picking out chicks, avoid the ones who are trying to eat their siblings, and if you ever have babies hatch that do this, cull, do not breed them.Not in my experience. The very few chicks I've had that pecked at eyes stopped after three or so pecks, and all the adults ever did was close their eye or move their head away. About 95% never pecked at eyes. Those that did came from high production breeds.
Baby chickens from less intensively farmed ancestry either never peck at eyes or stop of their own accord, as their instincts are more intact, more natural, and direct them to begin exhibiting normal behaviors from hatching onwards. Whereas baby chickens from intensively farmed ancestry, as I mentioned before, are known to commence cannibalism straight from hatching onwards, and as a rule not as an exception, not driven by malnourishment; it's just what their instincts are directing them to do. They view their own kind as food.
It's an instinctual aberration we bred into them. When a normal baby chicken hatches, it begins pecking at objects on the nest floor, not it's mother's face, from its earliest hours. One of the first things it eats are particles of its own eggshell; its instincts tell it to seek things on the ground to eat. Normal baby chickens don't have this confusion about eyes as food sources. Just like wild birds; can you imagine a world where wild birds ran the risk of losing their eyes to their own chicks? There would be much less in the way of wild birds. But that's unheard of; wild birds do not have this trait of pecking at their parent's eyes, or need to be taught not to.
When an abnormal baby chicken hatches, its warped instincts tell it to seek nourishment from the eyeballs, feet, and bodies of its own kind, not seek it elsewhere like on the ground. It will often ignore nourishment from elsewhere to continue to attempt to consume its own kind. You can spot these in a normal flock, walking around fixated on the eyes of their own kind, or whatever body part they are predisposed to attack and consume. These are not learned behaviors in the individuals exhibiting them, and they cannot be unlearned. They were gradually bred into them. They can be bred out over generations if you prevent the animals acting on them, but a dormant behavior is still genetically viable, so just because you prevent them acting on it does not mean they won't breed it on. You have to stop them acting on it for many generations and breed the least inclined in order to breed it out.
This is actually why we have cannibalism in the first place. Cannibalistic hens who were good layers were debeaked, and/or had spectacles and red lights etc applied to stop them, but were still bred, not culled. They were stopped from acting on it, but still bred, and so passed on their incorrect instincts, because natural selection dictates that any animal surviving to breeding age should pass on its traits because they served it well enough to enable its survival. Hence, they are viable and successful traits, even if only within abnormal environments we keep them in.
This isn't some random, abstract idea, it's been proven in studies, and some breeds are noted as being heavily genetically predisposed to cannibalism, and it is not caused by malnourishment, though in cannibalism-prone breeds that can trigger it...
But, again, in non-cannibalistic breeds, malnourishment does not trigger cannibalism. They starve instead.
Cannibalism is something you can breed in, or out, over as little as 5 to 7 generations, depending on how you keep them, what diet you keep them on, and the all important aspect of which birds, exhibiting which behaviors, you choose to breed on.
Best wishes.