Its the time of year to start molting where I live. They usually molt from somewhere in late summer to winter. I have heard some people say roosters molt slowly throughout the year, not sure if that is true.
For me? It takes quite a while. Usually they stop laying in the fall through winter and...
Check their butts for wounds and pin feathers. Look under the vent for wounds and in areas where they are missing feathers for pin feathers. Pin feathers would mean molting. A wound may mean flystrike, hoping not, but its better to be safe than sorry.