Unfortunately I don't have a solution for you most likely but I will share what caused the mouse population to decline to pretty much zero in my yard this year.
I had mice getting into my sheds and they were starting to get everywhere else except the house. All of a sudden I noticed the mouse population declining and now I only see evidence of old mouse activity, no real sign of recent activity. I had been using traps and moth balls with some success as well as clearing a lot of brush from the sides of my property but I knew the lack of mice was not due to that.
I finally discovered what has been happening. My daughter was playing under the white pines on the edge of our yard when she pointed out 3 wierd looking globs of fur on the ground. They were owl pellets and when we disected them we found all kinds of mouse bones, skulls, fur, etc. I guess that doesn't help much unless you can find a way to get some owls to show up for you.
We've always had hawks and the neighbors cats around and they probably helped keep the mice from getting too far out of control but man, once the owl or owls showed up the mice were gone. I just hope the owls don't disappear or the mice might come back. Now, if I can only get the owls to dig the darn moles out too!
