Well, I can prevent them from eating chicken. As long as there are no dead birds lying around ( which there certinaly would not be) or any birds with major cuts ( I make sure they don't hurt them selves as much as possible) So as long as I have a say in it my birdies are NOT cannibals !
As was already pointed out... Chickens cannot be cannibals as cannibalism is a human trait, not a chicken trait..