Wow, a chicken eating a bird! I've never seen that yet. Come to think of it, even though I'm surrounded by woods, I never see ANY birds flying and hopping about. Hmmmm, maybe they know chickens are dangerous? LOL
We have a rabbit in our yard that grazes right with the chickens. They used to chase the rabbit, but now, I think they're used to seeing it, so they don't bother. Rabbits are very vigilant....Always watching for predators, so I think when the rabbit is out, it's more than likely safe for the moment.
It doesn't surprise me at all that a hen would eat a baby bird.....Easy prey......Just never though about that.