https://www.backyardchickens.com/threads/proper-design-of-roost-bars.1197058/#post-18939241
this thread talks about a science study for the best roosts. maybe apply that information when looking for branches. its roughly a 1.5" diameter slightly boxy branch.
Mine are rose of sharon (a prolific woody weed) and some random thin tree that we wanted gone. But both of those arent bark heavy so I'm not sure about that. I didnt consider risk of using natural materials as mine spend all day outside anyway. They change up sleeping positions every night and...