they are not a real threat to your chickens, but you don't want rodents around your coop. They often eat eggs in addition to eating and fouling feed. you could use a repeating mouse trap or one where they enter and get zapped, neither one will harm the chickens or the environment. If you can't find one (which you should be able to) look up "home made repeating mouse trap" on youtube, there are some good ones that you can make for free with stuff you find around the house or shop. I've made a "teeter totter" style one before and they work fine.
