I was going to point to my story, then someone else posted something similar. Read below.
These birds obviously knew they were the same species. On my story, I will give credit that the bird added was new, so that gives the hen some slack, but the chicken it killed beforehand wasn't.
I think it's more of injuries than anything, and likely a survival instinct deep down. Chickens will eat other chickens, and as people are claiming here, they might even eat you if you died in their yard. But a very important factor that only a few are mentioning is
blood. You
could die in their yard, they
could eat you,
but, it's actually highly unlikely, unless, of coarse, you died by busting your head open on a rock or had a pitchfork spear you through. You just lying there, dead from let's say a heart attack, isn't going to get them to eat you. They might not even go near you. Or if they do, it's to use your corpse as a comfy perch. What's going to get them to eat you is the blood. If your head is wide open or your guts are poured out, they're going to see blood, they're going to see meat, they're going to see something that's going to attract predators if it's not cleaned up, and they're gonna go after it. Otherwise, no.
Unfortunately, as horrified I've been upon discovery, I have had chickens due in my coops, and their corpse be trampled on the floor for days and not get eaten by the other chickens. (Please know, each of these times, these chickens weren't in my care and was often the fault of a careless farm hand.) When these said chickens died, there was no blood, so therefore the other chickens didn't go after them. They most likely avoided it, possibly paid their respects, then as time went on without a proper removal, the chickens eventually saw it as part of the ground and walked over them. None of these times did the chickens eat the ones who died. And even if they were starving, I don't think they would have either. They would likely go after the living chickens before they went after the one dead on the ground for days. (And on the note of starving chickens. I did have a chicken who was on her way to starving to death due to a harsh pecking order. She had a sibling who stuck by her side, and never once did she try eating that sibling. She was definitely an extreme case, and was moved to a flock that had such a good pecking order that she was able to fully recover and live a happy life like a normal chicken.)
I do believe chickens care for each other. I've even had cases where I've lost chickens due to a broken heart of losing their bonded friend. Then I've heard the stories of the flock losing a respected older hen like what you've said. And for the most part, though chickens are very cannibalistic, they need a reason to eat each other. Aside from the extreme cases like that factory hen I mentioned in the chicken barns, or that Orpington
@CalebMS had, most of the time, they won't even kill each other just to eat each other. And personally, as I'm writing this post, I'm thinking that it's all about survival. Think of them eating eggs. In a healthy environment and normal flock, the chickens will only eat their eggs if it broke in the nesting box and therefore needed to be cleaned up. On eating each other, blood, injuries, and anything in the likes would call predators in the wild. By them eating the bleeding chicken, it might very well be their way of "cleaning up the mess" and ensuring that it will not be calling in predators that will kill the whole flock.
