First, I am blessed with a Bombay cat who understands her job and is excellent at it. She makes a point of showing me each mouse she catches. That said, not all cats are good mousers.
Take the time to determine the routes the mice take. Put the traps there. I have a couple of areas that are off limits to my cat. I have learned that I don't even have to bait the traps if I place them on the routes the mice normally follow.
"Good decisions come from experience. Experience comes from bad decisions." ... Mark Twain
At the Sustainable Food & Farming Conference, the owners of Singing Frog Farm recommended getting the most active and inquisitive cats at the shelter, the ones that really chase toys or track anything in the window. They also recommended keeping them a little underfed (I'd be careful about this), as they described rodents as "sustenance hunting", and birds as "sport hunting". They described their rodent to bird carcass ratio as hundreds of rodents to one bird. They figured they find about one bird per cat per year, and probably a rodent per day. I also hate the impact cats have on wild birds. however this approach does get at the main cause of bird population declines, that we feed cats that therefore do not decline in population along with their prey sources. I don't want anyone starving their cats, but it is better for them and the birds to keep them lean.
This is all just my opinion based on a flawed memory
Spring has sprung. My garden is gorgeous. I had a problem with brown mice digging up buried compost a few months ago, set traps and got two (I know there are more, but that seemed to make them less visible for a while).
Today I went outside to look at a strange bird in the garden and I spotted a brown mouse nibbling on a ZUCCHINI! Not my sunflowers or the rabbit pellets but a zucchini on the plant. My rabbits won`t eat zucchini if I pay them, and these little..... sorry, anyway.
Going to put down traps. We have heavy cat and hawk pressure here, so I can see why they're not climbing up the (very exposed) sunflowers but rather staying under the mob planted zucchini. I'm having great results from crowd planting and heavy mulch in our current drought but not sure about how this is going to work out if I'm just creating a massive shady playground for rodents.
(bright side, I planted 25+ corn seed and it looks like they got zero. Also seedling planting has been much better this year, I moved the seedling station away from the house where I know they have some protection, now to reach my seedling flats they need to cross the dog's yard and climb up a table. So far, nobody has found that worth the risk.
Electrified "rabbit mesh" could solve the problem. I saw evidence of this with folks who had installed it to keep rabbits out - but placed a cat inside the mesh overnight for several weeks to get those "trapped" inside.
The first year they found they had trapped mice INSIDE the mesh, which very effectively excluded the cat, and the mice population exploded as they were safe from all but aerial predators.
Digging down at least 18 inches to preclude digging under, and enclosing the garden in a metal (roofing) fence also works great as it is unclimbable.
Lorinne Anderson: Specializing in sick, injured, orphaned and problem wildlife for over 20 years.
Diego Footer on Permaculture Based Homesteads - from the Eat Your Dirt Summit