You're calling the Crow dumb? The bird tha would outsmart any cat, and if threatened and they don't like your cat, they will not just attack it, they will gang up and attack it strategically with a whole flock, or murder as it where, and probably kill the cat.
So true, Crows are very smart, one of the few animals that will use -tools- for a purpose, e.g: food that is out of reach.
There are other animals you keep mice away, and I'm sure NZ has their own mice predators. Cats are not as effective mouse hunters as cat overs like to make out.
I don't have mice around my house out in nowhere, probably because there are two other predators around, foxes, and more important for the mice, another tiny to creature I don't know the fish name for, but it looks like a ferret, and they are most effective mice eradicators.
Sadly, I believe mice are an invasive introduced species to NZ also, the reason those flightless birds exist there is because
there was little to no other threatening wildlife there so flying wasn't essential to survival.
But mice are something humans can take care of, no need of cats.