I am really sorry to sound like a spoilsport, but BARK can be a disaster for chickens. When it gets wet, it can grow a sort of mould that causes asperghilosis (sp), an often fatal respiratory disorder. Straw is best, so long as you rake it up often enough, and the girls just love it. Wood chips/shavings are great, but must not be hardwood (yes, chookies got splinters and bumblefoot), and must not be from chemically treated timber. So many potential probs, but hey ho.
PS. we all look after our chickens differently, and all chickens are themselves individuals, but when asked, i like to share my own experience, hoping that by doing so, itll save you from the same hard lessons some of us have learnt from.