This time of year critters of all kinds are looking for a nice safe, warm place to spend the winter. For many this can lead to field mice or rats in their coops. I mean, what better place for a family of mice to bed down? Soft bedding on the floor, a convenient food source, a water source, and if your coop is inside an enclosed run, safety from predators. Although chickens will kill and eat mice if they find them, once the chickens are asleep, the mice are free to come and go at will.
Chickens sleep extremely soundly and it's not unheard of for mice and rats to literally chew on chickens' feathers and feet, or pull out feathers to use for nest bedding while the hens sleep, so for this reason as well as the diseases rodents can carry, you certainly don't want mice in your coop! It's a good idea to 'listen' to your flock. If all of a sudden they seem to not want to go to roost in the coop at night, there's probably a good reason why not. NEVER force them in. Instead try and figure out why.
It could be mites - in that case a thorough coop cleaning, scrub down and application of DE is in order - or it could be a family of mice. Check the corners, raking the bedding away, and also check all the nesting boxes. If you do find rodents (or evidence of rodents) there are a couple of things you can do.
NOTE: We DO NOT recommend putting out traps or poison for obvious reasons. There's just too much chance of the chickens or another animal being harmed by accident. Instead we recommend taking these preventative measures against rodents:
1) No Openings Larger than 1/2" - Mice, as well as snakes and weasels, can get through a hole as small as one inch. Staple 1/2" hardware cloth over all the windows and vents in your coop and be sure all other holes are plugged.
2) Plant Mint - Mint is a natural rodent repellent. Plant some mint around the coop and run. Sprinkle fresh or dried mint in the coop and nesting boxes. (I also make an all natural lavender mint spray that I use as a coop refresher and rodent repellent)
3) Get a Barn Cat - Our cat does a great job of keeping our barn and chicken yard free of rodents. He doesn't generally have access to the run, but just his presence around the perimeter is a deterrent. A dog can have the same effect if it spends time around your chicken yard.
4) Don't Leave Feed in the Coop - Chickens can't see well in the dark anyway, so they don't eat at night. Remove the feed from the coop to remove rodents' food source.
5) Make The Roosts Wider - To prevent rodents from chewing on your hens' feet at least, replace your roosting bars with 2x4's with the 4" side facing up. This way the chicken's feet are not exposed - covered by their bodies from the top and the board on the bottom. Having a wider roost also prevents frost bite, so a wider roost is recommended regardless. (Chickens don't necessarily need to curl their feet like wild birds when they sleep, and actually prefer to sleep flat-footed)
Making these few small changes can make your coop inhospitable for local rodents who hopefully will find another place to call home.