Basking. Well, bathing in the warmth of the sun.
Dirt don't hurt
Chickens need access to dirt or dry sand. It's how they clean themselves. My little ladies scratched their way through the dirt-digging in impressions big enough for their entire bodies. After their spots were made all comfortable they settled into their dug-outs rolled around and ruffled their feathers until they were covered with the soil-which they later shook off. All clean!