Things you can try adding that aren't food: wood ladders and sawhorses, old patio furniture, pallets or scrap wood with nails covered/removed leaning against a fence, planters with dust bathing materials - the aim is to give them a variety of things to explore that get them up and down and under and around. Piles of hay or dried leaves or grass are good boredom busters too - just dump it and the chickens will busy themselves digging around and reorganizing it for you.
