I know Yorkies were bred to kill rodents back in the day, so I was wondering how your pup does with a hamster (if you have one).
My son just got a hamster for his birthday and anytime someone talks to the hamster in his cage Isla goes crazy and starts jumping on your leg. If Rhino (the hamster) is in his exercise ball Isla will chase the ball and nose it if the hamster stops. It's comical but I don't think Rhino enjoys it much. I just think it's funny that the dogs are more interested in him than the cat--who kills voles all summer long!
P.S. Rhino really is a good hamster. He has a great personality and temperment which makes him really fun and I bet he would like to snuggle with one of the dogs if they gave him a chance!