I totally understand your angst! At a couple of points in time over the years I had a mouse and/or rat flurry but the situation resolved, and nonlethally actually. If you can put all food away at night (chicken food and beyond - even that in dishes) and endure getting crumbs up (I know - not easy!)), this will really help. You can also try Mouse Magic by Bonide - a nontoxic mouse repellent that uses spearmint and peppermint. Some Ace Hardware stores carry it. You put the little packets anywhere that you don't want mice. Reportedly, cotton balls dipped in peppermint oil also work. (I do not put any of this stuff too close to the chickens in case the scent bothers them). I will never use sticky traps because of the slow torment of a death that they are, so those and poison ...never. I also did a major cleanup in the building within which my coop resides and found places that the rats were getting too cozy - they had used straw and towels and whatever else to make places for themselves when it was cold out. Cleaned it all out, made sure no food anywhere, and they didn't come back (truthfully I also did some hav-a-heart trapping then).Coop is made inpenetrable by mice or rats (hopefully) so this also helps. And have been working on making the larger building inpenetrable too. Now that spring has sprung (sort of) it will be easier for you to get them all gone because they will have plenty of other options for food etc. Not fun, any of it - hope it gets better soon.
JJ
JJ