My first flock had to learn to roost on their own and managed to do it about the time they started laying.
After that, the adults teach the youngsters. To the point that when I open the integration pen the chicks start roosting on the top of it within a week.
Mine aren't pine branches, they're the trunks of saplings.
Between the size of my wrist and the size of my DH's wrist. *hunts for a ruler*
2-3 inches diameter, I suppose.
One thing with round roosts -- I've noticed that people talk about cleaning poop off their roosts and I'm there thinking...
Bamboo might be too slippery to make good roosts.
All mind are natural branches because scrub oak and pine saplings are weeds on this property. Pity I can't teleport a couple your way. :D