We have a large tree that has limbs hanging over part of the coop. Two of my girls have started roosting in the limbs. They can get down fine and I have no problems with them being up there. But once it starts to get cold will they move to the coop? I'd think it would be pretty chilly up there during the winter. (Winter in SE GA so no snow for us but cold enough for my blood!)
If they were my hens they would be locked up 24 hours a day in the coop until their little brains are re-programmed to sleep in the coop. Lots of predators also like to get in the trees at night - coons and possums are the two that come to mind right off.
I have some GREAT trees my chickens roost in during the day, but the girls (and boys) always go back to the coop(s) at night. Sometimes they're napping up there, sometimes they're just sitting and looking around, often next to a buddy of theirs. I'd be concerned if they wanted to stay up there to roost AT NIGHT. Like Gritsar said, I'd lock 'em in the coop until they got the knowledge stamped into their little brains that COOPS are NIGHT SECURITY.
Your biggest problem will be if and when a great horned owl locates them. They are skilled at removing chickens from trees.
