Hi BBchicks,
This is my third year with chickens in my backyard. I did not appreciate the danger of mice until I inadvertently created the perfect environment for them. (I left food in the coop and insulated it so they had a nice cozy home all winter). They completely overran my coop and my backyard. Here is what I learned:
Mice reach sexual maturity at a few months of age and from then on produce 8-15 babies every 21 days or so.
Their poop can be hazardous to your health.
They are not strict vegetarians and will chew on chickens' feet while they are roosting. Chickens sleep deeply and sometimes don't notice.
Saving baby mice may seem the right thing to do, but from your chicken's perspective, it's not.