Our feral/semi-feral cats are EXCELLENT hunters of all things smaller than them. However, they will NOT mess with the chickens, and do go sleep in the coops often at night or if it's beastly hot.
I trust them even with baby chicks now, mostly because the chicks always have Momma Hen over them, and our LH hens have no qualms in whipping cat butt. And well, a JG, English Orp and 'Dotte are all bigger and meaner than a cat. The banty hens aren't big enough, but well, they get the banty roos to stay with them while broody with chicks. The cats HAVE lost to the roos, always, even a little dinky marshmellow fluffy butted 20 week old banty Cochin. If a roo is there, the cats are very very careful to not get whipped.