My house is surrounded by fields and there is a huge barn behind my house. I have owls, vultures, snakes, groundhogs, racoons, etc. that live in/around the barn. They all find their way to my house daily, I'm sure. However, they are not enough to kill all of the field mice.
Sounds like I need to start working on a design and patent.
I'd spend so much money on bait and traps that I wouldn't be able to afford food for the grill.