Sawdust: ok, but tends to pack down quickly unless turned frequently Pine peelings/bark, or shredded paper: ok but needs to be a deeper layer (15cm+), and turned frequently
Dry straw: ok if turned regularly, but won’t cope if it gets too wet
Hay: don’t use, as it doesn’t absorb moisture well, packs flat when wet, and can harbour moulds
Once litter has manure in it, and the birds are turning it over regularly, it will heat up, similar to a compost heap, but not as hot.
The longer you leave a deep litter system, the more it will decompose. Heat, oxygen and bacteria turn the manure and shavings into a fine, almost, powder-like consistency, making it easy to handle.
Compost expert Ben Elms uses a deep layer of bark on the floor of his run. He adds the daily kitchen scraps to it, and his birds dig it in. Once a year, he digs it out and uses it around fruit trees.