I have had great luck with plain old landscaping wood chips in my chicken run; unlike mulch bark they don't tend to hold moisture and get damp. They are cheaper than shavings, so I only use shavings in the house.
Softwood landscaping wood chips placed in a coop and raked over every couple of weeks will slowly decompose in place; I like to take mine out once a year and put them around my fruit trees, renewing the mulch and doing a lot of my fertilizing at the same time. At around six months in the cycle, I top them off. I've let the same batch go with occasional additions for nearly two years with no problems; unfortunately I had a outbreak of leg mites, so I wound up cleaning them out and spraying the premises with a Neem oil solution. I cleared it out, hit it with Neem oil, laid in fresh shavings, and then hit it every week for a month with the Neem oil and treated the birds concurrently. Worked great.