@bonifartius Cats only kill mice really and that's only if they are hungry. Rats are too big for a cat, so they generally don't risk attacking a rat unless they're starving, as there's a good chance the rat will injure the cat.
A bell on the cats collar helps with birds, but only during the day.
@Suiseiseki we had a dead rat here with bites in the neck. either was a stray cat or a weasel, maybe a fox? either way if a cat acts as repellent thats enough for me ;)