Scratch grains, fresh eggs and warm bedding are all the encouragement mice need to move into a chicken coop. Unfortunately, poisons and traps also will hurt your birds, so getting rid of rodents in the hen house can be challenging. Chickens will eat small, young mice, but adults are too large. It is important to control the rodent population in you chicken coop because mice will eat the chicken’s feed and could bring disease.
Starve them out. Those mice are only there for the food and they'll stay as long as there is food. Store feed in covered galvanized cans, and don’t leave feed out for free choice while you have a rodent problem. Feed small amounts several times a day, and do not leave feed in the coop overnight. The chickens don’t need it, and the mice will eat it.
Check for entry points. Mice can get through very small spaces. Be sure that any possible entry points are boarded up or covered with wire mesh no larger than ½ inch by ½ inch. Also, check the wire covering the run area of your coop. The holes in the mesh should not be larger than ½ inch by ½ inch. Mice also will burrow under the coop to gain entry. Bury a stretch of wire mesh up to 18 inches deep around the base of the coop.
Turn the litter regularly. Turned litter and bedding stays dry, reducing odor and the possibility of disease. Disturbing the litter on a regular basis also disturbs rodent nests.
Set up safe traps. Spring-loaded traps and poison packets can kill your chickens. Live traps capture rodents for removal. Mix equal parts cornmeal and plaster of Paris for the bait in the trap. Make sure the bait is out of reach of the chickens. If the mice take the bait but don’t spring the trap, the plaster/cornmeal mixture will harden in the stomach and kill the rodent. Chickens may try to eat the dead rodent but won’t be harmed by poisons.