Be careful with this. If you put traps where the chickens can get to them, the chickens will be injured or even killed by the traps. If you use poison, if any dying rats or mice make it to where the chickens are, the chickens will probably eat them and they will be poisoned as well. Chickens love to eat mice and baby rats. I've always had barn cats to deal with my rodents. I introduce the cats to the chickens while they're still kittens. The cats learn not to bother the chickens and they take care of mice and rats. However, cats normally don't, and shouldn't eat mice and rats, so you have to give the cats food, water and and cozy place to sleep.