You might want to consult with a professional. But if I were you I'd do something about the food first. Maybe try a combination of different traps near their tunnels and pathways/along walls. We had a problem a couple years ago with them getting into the crawl space/garage/dog food. We used a combo of sticky glue traps (use with caution do not want to catch a chicken!), live cage traps which got the full grown rats, and we also used poison. I was worried about our dog maybe catching a poisoned rat (we didn't have chickens then) but that never turned out to be a problem. I think maybe the poison was the kind that gets activated when they leave to drink water? Again that's where something like a pro would be more knowledgeable especially towards your specific situation...