I have a cat now who helps in that department and had a West Highland Terrier who was great with vermin control as well - and left my flock alone (he was scared of them). I'd have another Westie over another cat any day.
My cairn terrier had a mouse in the shelter she hunted relentlessly. I LOVE that breed- most favorite breed ever. Same size as a a Westie, but our girl came from Texas and so broke the mold. Our vet said he's never seen one that big, amd called her the great dane of the breed.

The dogs seem to do more digging to get to the voles, whereas the cats wait and watch patiently. They harass the squirrels, too. And then there are the snakes.... so long as they leave my birds and eggs alone {and aren't venomous}, we're good.